kip
homeostatic regulation
a lower limit to atmospheric co2 concentrations over the past 800,000 years
e. d. galbraith, s. eggleston 2017
dx.doi.org/10.1038/ngeo2914
temporal scaling of carbon emission and accumulation rates: modern anthropogenic emissions compared to estimates of petm-onset accumulation
philip d. gingerich et al. 2019
http://dx.doi.org/10.1029/2018pa003379
humans are pumping carbon dioxide into the atmosphere at a rate nine to 10 times higher than the greenhouse gas was emitted during the Paleocene-Eocene Thermal Maximum (PETM), a global warming event that occurred roughly 56 million years ago.
The results suggest if carbon emissions continue to rise, the total amount of carbon dioxide injected into the atmosphere since humans started burning fossil fuels could equal the amount released during the PETM as soon as 2159.
"You and I won't be here in 2159, but that's only about four generations away," said Philip Gingerich, a paleoclimate researcher at the University of Michigan and author of the new study in the AGU journal Paleoceanography and Paleoclimatology. "When you start to think about your children and your grandchildren, and your great-grandchildren, you're about there."
Scientists often use the PETM as a benchmark against which to compare modern climate change. But the new study shows we're on track to meet this benchmark much sooner than previously thought, as the pace of today's warming far outstrips any climate event that has happened since the extinction of the dinosaurs.
"Given a business-as-usual assumption for the future, the rates of carbon release that are happening today are really unprecedented, even in the context of an event like the PETM," said Gabriel Bowen, a geophysicist at the University of Utah who was not connected to the new study. "We don't have much in the way of geologic examples to draw from in understanding how the world responds to that kind of perturbation."
The exact environmental consequences of PETM-like carbon levels are unclear, but the increased temperatures will likely drive many species to extinction with the lucky ones being able to adapt or migrate, according to Larisa DeSantis, a paleontologist at Vanderbilt University who was not connected to the new study. In addition, it will take thousands of years for the climate system cool down, she said.
"It's not just about 100 years from now; it's going to take significant periods of time for that carbon dioxide to make its way back into the Earth's crust," DeSantis said. "It's not a short-term event. We're really committing ourselves to many thousands of years of a warmer world if we don't take action quickly."
Studying past climate change
The PETM was a global warming event that occurred roughly 56 million years ago. Scientists are unsure what caused it, but during the event massive quantities of carbon dioxide were released into Earth's atmosphere, rapidly spiking global temperatures by 5 to 8 degrees Celsius (9 to 14 degrees Fahrenheit). Average global temperatures during the PETM peaked at about 23 degrees Celsius (73 degrees Fahrenheit), about 7 degrees Celsius (13 degrees Fahrenheit) higher than today's average.
Scientists think that during this time and the warm period that followed, the poles were ice-free and the Arctic was home to palm trees and crocodiles. It's not the hottest Earth has ever been, but the PETM was the warmest period since the extinction of the dinosaurs 66 million years ago.
Scientists can't pin down exactly how much carbon was injected into the atmosphere during the PETM or exactly how long the event lasted. But their best estimates say between 3,000 and 7,000 gigatons of carbon accumulated over a period of 3,000 to 20,000 years, based on ocean sediment cores that show changes to carbonate minerals laid down during this time.
The massive carbon release and temperature spike drastically altered Earth's climate, causing a major extinction of organisms in the deep ocean that are a key link in the marine food web. Land animals got smaller and migrated north to cooler climates. Some groups of modern mammals, including primates, appeared for the first time soon after the PETM, but scientists are unsure whether this happened as a direct result of the rapid environmental change.
Comparing past with present
Climate scientists use the PETM as a case study for understanding what environmental changes might happen under current human-caused climate change and when those changes might take effect. But they can only average carbon emissions during the PETM over the whole duration of the event -- thousands of years. They don't know what those emissions rates were like on a yearly basis, so it's difficult to compare them to the pace of carbon emissions today.
In the new study, Gingerich found a way to mathematically compare modern carbon emissions to PETM emissions on the same time scale. The results showed current carbon emission rates are nine to 10 times higher than those during the PETM.
"To me, it really brought home how rapidly and how great the consequences are of the carbon we're producing as a people," Gingerich said.
Projecting current emissions into the future, Gingerich found that if emissions continue to rise, we could be facing another PETM-like event in fewer than five generations. The total carbon accumulated in the atmosphere could hit the lowest estimate of carbon accumulated during the PETM -- 3,000 gigatons -- in the year 2159. It would hit the maximum estimated emissions -- 7,126 gigatons -- in 2278, based on Gingerich's calculations. Humans have emitted roughly 1,500 gigatons of carbon as of 2016.
"The fact that we could reach warming equivalent to the PETM very quickly, within the next few hundred years, is terrifying," DeSantis said.
The findings suggest scientists may not be able to predict the environmental or biological changes that will happen in the coming years based on what happened during the PETM because today's warming is occurring so much faster, according to DeSantis. What makes predictions harder is that today's climate starts from a cooler baseline than the PETM and the species that inhabit Earth are different than those of 56 million years ago.
"It's hard to compare biotic effects because the world during the PETM was quite different," DeSantis said. "We live in a very different world today, with different groups of animals, with humans being the dominant species... but we know there are many negative consequences of dramatic warming on vast numbers of species, including our own."
abstract The Paleocene‐Eocene thermal maximum (PETM) was caused by a massive release of carbon to the atmosphere. This is a benchmark global greenhouse warming event that raised temperatures to their warmest since extinction of the dinosaurs. Rates of carbon emission today can be compared to those during onset of the PETM in two ways: (1) projection of long‐term PETM rates for comparison on an annual time scale; and (2) projection of short‐term modern rates for comparison on a PETM time scale. Both require temporal scaling and extrapolation for comparison on the same time scale. PETM rates are few and projection to a short time scale is poorly constrained. Modern rates are many and projection to a longer PETM time scale is tightly constrained — modern rates are some 9–10 times higher than those during onset of the PETM. If the present trend of anthropogenic emissions continues, we can expect to reach a PETM‐scale accumulation of atmospheric carbon in as few as 140 to 259 years (about 5 to 10 human generations).
Plain Language Summary
The Paleocene‐Eocene thermal maximum (PETM) is a global greenhouse warming event that happened 56 million years ago, causing extinction in the world's oceans and accelerated evolution on the continents. It was caused by release of carbon dioxide and other greenhouse gases to the atmosphere. When we compare the rate of release of greenhouse gases today to the rate of accumulation during the PETM we must compare the rates on a common time scale. Projection of modern rates to a PETM time scale is tightly constrained and shows that we are now emitting carbon some 9‐10 times faster than during the PETM. If the present trend of increasing carbon emissions continues, we may see PETM‐magnitude extinction and accelerated evolution in as few as 140 years or about five human generations.
climate regulation
living in rocks
do microbes control the formation of giant copper deposits?
fernando tornos et al. 2019
http://dx.doi.org/10.1130/g45573.1
predict that future multidisciplinary studies will prove that microbes have a key control on the precipitation of metals in these shallow environments.
Their case study is based on the unusual Las Cruces deposit in southwest Iberia, where a significant part of the high-grade copper ore occurs as thick, massive veins of copper sulfides. Tornos and colleagues have direct evidence that the mineralization is currently being formed there in relationship with active aquifers and in an area isolated from the surface by a thick layer of marl. Thus, the place is ideal for tracking for anaerobic microbes.
With the help of the mining company, First Quantum, the team was able to extract pristine samples that had never been in contact with the atmosphere.
Different microbiological techniques and detailed electron microscope studies have shown that copper sulfides are precipitating today in relationship with colonies of sulfate-reducing microbes. The nanometer-sized crystals of covellite are embedded in the polymeric compounds that encapsulate bacteria. These crystals coalesce, later forming the big veins. However, much more work is needed in order to know to which extent these processes are global and if microbes control most of the formation of the secondary copper deposits.
abstract The formation of secondary copper deposits, the source of more than half of the world’s production, is usually interpreted as abiogenic. In this study of the Las Cruces deposit (southwestern Spain), in situ hybridization and scanning electron microscopy analysis together with integrated genomic and bioinformatic studies on cultures provide compelling evidence that a microbial community controls the current formation of the secondary copper mineralization. The cementation zone of this deposit contains abundant microbial life dominated by sulfate-reducing bacteria that coexist with methanogens and with other prokaryotes having unknown roles. Fractures in the primary massive sulfides are coated by extracellular polymeric substances in which the microbial cells are embedded. Covellite crystals have nucleated within these microbial aggregates, accreting and forming large crystals attached to the vein walls. These results strongly suggest that in situ microbial sulfate reduction can control the formation of secondary copper deposits. Equivalent processes could be widespread in similar deposits elsewhere, but they are probably overlooked due to the presumed low capability for fossilization of the microbes.
the biomass and biodiversity of the continental subsurface
c. magnabosco et al. 2018
https://doi.org/10.1038/s41561-018-0221-6
life in deep earth totals 15 to 23 billion tonnes of carbon—hundreds of times more than humans
terry collins, katie pratt 2018
https://deepcarbon.net/life-deep-earth-totals-15-23-billion-tonnes-carbon
deep microbial proliferation at the basalt interface in 33.5–104 million-year-old oceanic crust
yohey suzuki et al. 2020
http://dx.doi.org/10.1038/s42003-020-0860-1
Newly discovered single-celled creatures living deep beneath the seafloor have given researchers clues about how they might find life on Mars. These bacteria were discovered living in tiny cracks inside volcanic rocks after researchers persisted over a decade of trial and error to find a new way to examine the rocks.
Researchers estimate that the rock cracks are home to a community of bacteria as dense as that of the human gut, about 10 billion bacterial cells per cubic centimeter (0.06 cubic inch). In contrast, the average density of bacteria living in mud sediment on the seafloor is estimated to be 100 cells per cubic centimeter.
“I am now almost over-expecting that I can find life on Mars. If not, it must be that life relies on some other process that Mars does not have, like plate tectonics,” said Associate Professor Yohey Suzuki from the University of Tokyo, referring to the movement of land masses around Earth most notable for causing earthquakes. Suzuki is first author of the research paper announcing the discovery, published in Communications Biology.
Magic of clay minerals
“I thought it was a dream, seeing such rich microbial life in rocks,” said Suzuki, recalling the first time he saw bacteria inside the undersea rock samples.
Undersea volcanoes spew out lava at approximately 1,200 degrees Celsius (2,200 degrees Fahrenheit), which eventually cracks as it cools down and becomes rock. The cracks are narrow, often less than 1 millimeter (0.04 inch) across. Over millions of years, those cracks fill up with clay minerals, the same clay used to make pottery. Somehow, bacteria find their way into those cracks and multiply.
“These cracks are a very friendly place for life. Clay minerals are like a magic material on Earth; if you can find clay minerals, you can almost always find microbes living in them,” explained Suzuki.
The microbes identified in the cracks are aerobic bacteria, meaning they use a process similar to how human cells make energy, relying on oxygen and organic nutrients.
“Honestly, it was a very unexpected discovery. I was very lucky, because I almost gave up,” said Suzuki.
Cruise for deep ocean samples
Suzuki and his colleagues discovered the bacteria in rock samples that he helped collect in late 2010 during the Integrated Ocean Drilling Program (IODP). IODP Expedition 329 took a team of researchers from the tropical island of Tahiti in the middle of the Pacific Ocean to Auckland, New Zealand. The research ship anchored above three locations along the route across the South Pacific Gyre and used a metal tube 5.7 kilometers long to reach the ocean floor. Then, a drill cut down 125 meters below the seafloor and pulled out core samples, each about 6.2 centimeters across. The first 75 meters beneath the seafloor were mud sediment and then researchers collected another 40 meters of solid rock.
Depending on the location, the rock samples were estimated to be 13.5 million, 33.5 million and 104 million years old. The collection sites were not near any hydrothermal vents or sub-seafloor water channels, so researchers are confident the bacteria arrived in the cracks independently rather than being forced in by a current. The rock core samples were also sterilized to prevent surface contamination using an artificial seawater wash and a quick burn, a process Suzuki compares to making aburi (flame-seared) sushi.
At that time, the standard way to find bacteria in rock samples was to chip away the outer layer of the rock, then grind the center of the rock into a powder and count cells out of that crushed rock.
“I was making loud noises with my hammer and chisel, breaking open rocks while everyone else was working quietly with their mud,” he recalled.
How to slice a rock
Over the years, continuing to hope that bacteria might be present but unable to find any, Suzuki decided he needed a new way to look specifically at the cracks running through the rocks. He found inspiration in the way pathologists prepare ultrathin slices of body tissue samples to diagnose disease. Suzuki decided to coat the rocks in a special epoxy to support their natural shape so that they wouldn’t crumble when he sliced off thin layers.
These thin sheets of solid rock were then washed with dye that stains DNA and placed under a microscope.
The bacteria appeared as glowing green spheres tightly packed into tunnels that glow orange, surrounded by black rock. That orange glow comes from clay mineral deposits, the “magic material” giving bacteria an attractive place to live.
Whole genome DNA analysis identified the different species of bacteria that lived in the cracks. Samples from different locations had similar, but not identical, species of bacteria. Rocks at different locations are different ages, which may affect what minerals have had time to accumulate and therefore what bacteria are most common in the cracks.
Suzuki and his colleagues speculate that the clay mineral-filled cracks concentrate the nutrients that the bacteria use as fuel. This might explain why the density of bacteria in the rock cracks is eight orders of magnitude greater than the density of bacteria living freely in mud sediment where seawater dilutes the nutrients.
From the ocean floor to Mars
The clay minerals filling cracks in deep ocean rocks are likely similar to the minerals that may be in rocks now on the surface of Mars.
“Minerals are like a fingerprint for what conditions were present when the clay formed. Neutral to slightly alkaline levels, low temperature, moderate salinity, iron-rich environment, basalt rock — all of these conditions are shared between the deep ocean and the surface of Mars,” said Suzuki.
Suzuki’s research team is beginning a collaboration with NASA’s Johnson Space Center to design a plan to examine rocks collected from the Martian surface by rovers. Ideas include keeping the samples locked in a titanium tube and using a CT (computed tomography) scanner, a type of 3D X-ray, to look for life inside clay mineral-filled cracks.
“This discovery of life where no one expected it in solid rock below the seafloor may be changing the game for the search for life in space,” said Suzuki.
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video
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four direct measurements of the fine-structure constant 13 billion years ago
michael r. wilczynska et al. 2020
http://dx.doi.org/10.1126/sciadv.aay9672
the fine structure constant is a measure of electromagnetism -- one of the four fundamental forces in nature (the others are gravity, weak nuclear force and strong nuclear force).
"The fine structure constant is the quantity that physicists use as a measure of the strength of the electromagnetic force," Professor Webb says.
"It's a dimensionless number and it involves the speed of light, something called Planck's constant and the electron charge, and it's a ratio of those things. And it's the number that physicists use to measure the strength of the electromagnetic force."
The electromagnetic force keeps electrons whizzing around a nucleus in every atom of the universe -- without it, all matter would fly apart. Up until recently, it was believed to be an unchanging force throughout time and space. But over the last two decades, Professor Webb has noticed anomalies in the fine structure constant whereby electromagnetic force measured in one particular direction of the universe seems ever so slightly different.
"We found a hint that that number of the fine structure constant was different in certain regions of the universe. Not just as a function of time, but actually also in direction in the universe, which is really quite odd if it's correct...but that's what we found."
LOOKING FOR CLUES
Ever the sceptic, when Professor Webb first came across these early signs of slightly weaker and stronger measurements of the electromagnetic force, he thought it could be a fault of the equipment, or of his calculations or some other error that had led to the unusual readings. It was while looking at some of the most distant quasars -- massive celestial bodies emitting exceptionally high energy -- at the edges of the universe that these anomalies were first observed using the world's most powerful telescopes.
"The most distant quasars that we know of are about 12 to 13 billion light years from us," Professor Webb says.
"So if you can study the light in detail from distant quasars, you're studying the properties of the universe as it was when it was in its infancy, only a billion years old. The universe then was very, very different. No galaxies existed, the early stars had formed but there was certainly not the same population of stars that we see today. And there were no planets."
He says that in the current study, the team looked at one such quasar that enabled them to probe back to when the universe was only a billion years old which had never been done before. The team made four measurements of the fine constant along the one line of sight to this quasar. Individually, the four measurements didn't provide any conclusive answer as to whether or not there were perceptible changes in the electromagnetic force. However, when combined with lots of other measurements between us and distant quasars made by other scientists and unrelated to this study, the differences in the fine structure constant became evident.
A WEIRD UNIVERSE
"And it seems to be supporting this idea that there could be a directionality in the universe, which is very weird indeed," Professor Webb says.
"So the universe may not be isotropic in its laws of physics -- one that is the same, statistically, in all directions. But in fact, there could be some direction or preferred direction in the universe where the laws of physics change, but not in the perpendicular direction. In other words, the universe in some sense, has a dipole structure to it.
"In one particular direction, we can look back 12 billion light years and measure electromagnetism when the universe was very young. Putting all the data together, electromagnetism seems to gradually increase the further we look, while towards the opposite direction, it gradually decreases. In other directions in the cosmos, the fine structure constant remains just that -- constant. These new very distant measurements have pushed our observations further than has ever been reached before."
In other words, in what was thought to be an arbitrarily random spread of galaxies, quasars, black holes, stars, gas clouds and planets -- with life flourishing in at least one tiny niche of it -- the universe suddenly appears to have the equivalent of a north and a south. Professor Webb is still open to the idea that somehow these measurements made at different stages using different technologies and from different locations on Earth are actually a massive coincidence.
"This is something that is taken very seriously and is regarded, quite correctly with scepticism, even by me, even though I did the first work on it with my students. But it's something you've got to test because it's possible we do live in a weird universe."
But adding to the side of the argument that says these findings are more than just coincidence, a team in the US working completely independently and unknown to Professor Webb's, made observations about X-rays that seemed to align with the idea that the universe has some sort of directionality.
"I didn't know anything about this paper until it appeared in the literature," he says.
"And they're not testing the laws of physics, they're testing the properties, the X-ray properties of galaxies and clusters of galaxies and cosmological distances from Earth. They also found that the properties of the universe in this sense are not isotropic and there's a preferred direction. And lo and behold, their direction coincides with ours."
While still wanting to see more rigorous testing of ideas that electromagnetism may fluctuate in certain areas of the universe to give it a form of directionality, Professor Webb says if these findings continue to be confirmed, they may help explain why our universe is the way it is, and why there is life in it at all.
"For a long time, it has been thought that the laws of nature appear perfectly tuned to set the conditions for life to flourish. The strength of the electromagnetic force is one of those quantities. If it were only a few per cent different to the value we measure on Earth, the chemical evolution of the universe would be completely different and life may never have got going. It raises a tantalising question: does this 'Goldilocks' situation, where fundamental physical quantities like the fine structure constant are 'just right' to favour our existence, apply throughout the entire universe?"
If there is a directionality in the universe, Professor Webb argues, and if electromagnetism is shown to be very slightly different in certain regions of the cosmos, the most fundamental concepts underpinning much of modern physics will need revision.
"Our standard model of cosmology is based on an isotropic universe, one that is the same, statistically, in all directions," he says.
"That standard model itself is built upon Einstein's theory of gravity, which itself explicitly assumes constancy of the laws of Nature. If such fundamental principles turn out to be only good approximations, the doors are open to some very exciting, new ideas in physics.".
abstract Observations of the redshift z = 7.085 quasar J1120+0641 are used to search for variations of the fine structure constant, a, over the redshift range 5:5 to 7:1. Observations at z = 7:1 probe the physics of the universe at only 0.8 billion years old. These are the most distant direct measurements of a to date and the first measurements using a near-IR spectrograph. A new AI analysis method is employed. Four measurements from the X-SHOOTER spectrograph on the Very Large Telescope (VLT) constrain changes in a relative to the terrestrial value (α0). The weighted mean electromagnetic force in this location in the universe deviates from the terrestrial value by Δα/α = (αz − α0)/α0 = (−2:18 ± 7:27) × 10−5, consistent with no temporal change. Combining these measurements with existing data, we find a spatial variation is preferred over a no-variation model at the 3:9σ level.
the dipole repeller
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dipolerepeller
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cosmography of the local universe
a galactic-scale gas wave in the solar neighborhood
joão alves et al. 2020
http://https://doi.org/10.1038/s41586-019-1874-z
revealing the dark threads of the cosmic web
joseph n. burchett et al. 2020
http://dx.doi.org/10.3847/2041-8213/ab700c
The single-cell organism known as slime mould (Physarum polycephalum) builds complex web-like filamentary networks in search of food, always finding near-optimal pathways to connect different locations.
In shaping the Universe, gravity builds a vast cobweb-like structure of filaments tying galaxies and clusters of galaxies together along invisible bridges of gas and dark matter hundreds of millions of light-years long. There is an uncanny resemblance between the two networks, one crafted by biological evolution, the other by the primordial force of gravity.
The cosmic web is the large-scale backbone of the cosmos, consisting primarily of dark matter and laced with gas, upon which galaxies are built. Even though dark matter cannot be seen, it makes up the bulk of the Universe’s material. Astronomers have had a difficult time finding these elusive strands, because the gas within them is too dim to be detected.
The existence of a web-like structure to the Universe was first hinted at in galaxy surveys in the 1980s. Since those studies, the grand scale of this filamentary structure has been revealed by subsequent sky surveys. The filaments form the boundaries between large voids in the Universe. Now a team of researchers has turned to slime mould to help them build a map of the filaments in the local Universe (within 100 million light-years of Earth) and find the gas within them.
They designed a computer algorithm, inspired by the behaviour of slime mould, and tested it against a computer simulation of the growth of dark matter filaments in the Universe. A computer algorithm is essentially a recipe that tells a computer precisely what steps to take to solve a problem.
The researchers then applied the slime mould algorithm to data containing the locations of over 37,000 galaxies mapped by the Sloan Digital Sky Survey. The algorithm produced a three-dimensional map of the underlying cosmic web structure.
They then analysed the light from 350 faraway quasars catalogued in the Hubble Spectroscopic Legacy Archive. These distant cosmic flashlights are the brilliant black-hole-powered cores of active galaxies, whose light shines across space and through the foreground cosmic web. Imprinted on that light was the telltale signature of otherwise invisible hydrogen gas that the team analysed at specific points along the filaments. These target locations are far from the galaxies, which allowed the research team to link the gas to the Universe’s large-scale structure.
“It’s really fascinating that one of the simplest forms of life actually enables insights into the very largest-scale structures in the Universe,” said lead researcher Joseph Burchett of the University of California (UC), U.S.A. “By using the slime mould simulation to find the location of the cosmic web filaments, including those far from galaxies, we could then use the Hubble Space Telescope’s archival data to detect and determine the density of the cool gas on the very outskirts of those invisible filaments. Scientists have detected signatures of this gas for over half a century, and we have now proven the theoretical expectation that this gas comprises the cosmic web.”
The survey further validates research that indicates intergalactic gas is organised into filaments and also reveals how far away gas is detected from the galaxies. Team members were surprised to find gas associated with the cosmic web filaments more than 10 million light-years away from the galaxies.
But that wasn’t the only surprise. They also discovered that the ultraviolet signature of the gas gets stronger in the filaments’ denser regions, but then disappears. “We think this discovery is telling us about the violent interactions that galaxies have in dense pockets of the intergalactic medium, where the gas becomes too hot to detect,” Burchett said.
The researchers turned to slime mould simulations when they were searching for a way to visualise the theorised connection between the cosmic web structure and the cool gas, detected in previous Hubble spectroscopic studies.
Then team member Oskar Elek, a computer scientist at UC Santa Cruz, discovered online the work of Sage Jenson, a Berlin-based media artist. Among Jenson’s works were mesmerizing artistic visualisations showing the growth of a slime mould’s tentacle-like network of structures moving from one food source to another. Jenson’s art was based on scientific work from 2010 by Jeff Jones of the University of the West of England in Bristol, which detailed an algorithm for simulating the growth of slime mould.
The research team was inspired by how the slime mould builds complex filaments to capture new food, and how this mapping could be applied to how gravity shapes the Universe, as the cosmic web constructs the strands between galaxies and galaxy clusters. Based on the simulation outlined in Jones’s paper, Elek developed a three-dimensional computer model of the buildup of slime mould to estimate the location of the cosmic web’s filamentary structure.
abstract Modern cosmology predicts that matter in our universe today has assembled into a vast network of filamentary structures colloquially termed the “cosmic web.” Because this matter is either electromagnetically invisible (i.e., dark) or too diffuse to image in emission, tests of this cosmic web paradigm are limited. Wide-field surveys do reveal web-like structures in the galaxy distribution, but these luminous galaxies represent less than 10% of baryonic matter. Statistics of absorption by the intergalactic medium (IGM) via spectroscopy of distant quasars support the model yet have not conclusively tied the diffuse IGM to the web. Here, we report on a new method inspired by the Physarum polycephalum slime mold that is able to infer the density field of the cosmic web from galaxy surveys. Applying our technique to galaxy and absorption-line surveys of the local universe, we demonstrate that the bulk of the IGM indeed resides in the cosmic web. From the outskirts of cosmic web filaments, at approximately the cosmic mean matter density (ρ m ) and ~5 virial radii from nearby galaxies, we detect an increasing H i absorption signature toward higher densities and the circumgalactic medium, to ~200ρ m . However, the absorption is suppressed within the densest environments, suggesting shock-heating and ionization deep within filaments and/or feedback processes within galaxies.
the andromeda galaxy’s most important merger about 2 billion years ago as m32’s likely progenitor
richard d’souza, eric f. bell 2018
http://dx.doi.org/10.1038/s41550-018-0533-x
a hexagon in saturn’s northern stratosphere surrounding the emerging summertime polar vortex
l. n. fletcher et al. 2018
http://dx.doi.org/10.1038/s41467-018-06017-3
“The edges of this newly-found vortex appear to be hexagonal, precisely matching a famous and bizarre hexagonal cloud pattern we see deeper down in Saturn’s atmosphere,” says Leigh Fletcher of the University of Leicester, UK, lead author of the new study.
“While we did expect to see a vortex of some kind at Saturn’s north pole as it grew warmer, its shape is really surprising. Either a hexagon has spawned spontaneously and identically at two different altitudes, one lower in the clouds and one high in the stratosphere, or the hexagon is in fact a towering structure spanning a vertical range of several hundred kilometres.”
Saturn’s cloud levels host the majority of the planet’s weather, including the pre-existing north polar hexagon. This feature was discovered by NASA’s Voyager spacecraft in the 1980s and has been studied for decades; it is a long-lasting wave potentially tied to Saturn’s rotation, a type of phenomenon also seen on Earth in structures such as the Polar Jet Stream.
Its properties were revealed in detail by Cassini, which observed it in multiple wavelengths — from the ultraviolet to the infrared — using instruments including its Composite Infrared Spectrometer (CIRS). However, at the start of the mission this instrument could not peer further up in the northern stratosphere, which had temperatures around -158 degrees Celsius — some 20 degrees too cold for reliable CIRS infrared observations — leaving these higher-altitude regions relatively unexplored for many years.
“One Saturnian year spans roughly 30 Earth years, so the winters are long,” adds co-author Sandrine Guerlet from Laboratoire de Météorologie Dynamique, France.
“Saturn only began to emerge from the depths of northern winter in 2009, and gradually warmed up as the northern hemisphere approached summertime.”
A strange process at play within Saturn’s atmosphere sped up this warming: as air sank at the north pole, the upper hexagon warmed increasingly quickly, and the transport of air downwards made the abundance of several minor species more concentrated. The increased temperature allowed Fletcher and colleagues to study the polar vortex in infrared light.
“We were able to use the CIRS instrument to explore the northern stratosphere for the first time, from 2014 onwards,” adds Guerlet. “As the polar vortex became more and more visible, we noticed it had hexagonal edges, and realised that we were seeing the pre-existing hexagon at much higher altitudes than previously thought.”
This indicates that Saturn’s two poles behave very differently — there was no hexagon at the south pole, either at the cloud tops or above, when it was observed early in Cassini’s mission during southern summer. The northern vortex is also nowhere near as mature as the southern vortex, as it is cooler, and displays different dynamics from its southern counterpart.
“This could mean that there’s a fundamental asymmetry between Saturn’s poles that we’re yet to understand, or it could mean that the north polar vortex was still developing in our last observations and kept doing so after Cassini’s demise,” adds Fletcher. The Cassini mission came to an end in September 2017.
The presence of a hexagon way up in Saturn’s northern stratosphere, hundreds of kilometres above the clouds, suggests that there is much more to learn about the dynamics at play in the gas giant’s atmosphere.
A single, towering hexagonal structure that stretches up through the atmosphere would be unlikely given that wind conditions change considerably with altitude. However, by investigating the atmospheric properties in the northern region, Fletcher and colleagues also determined that waves like the hexagon should be unable to propagate upwards — they should remain trapped in the cloud-tops, as previously thought.
“One way that wave ‘information’ can leak upwards is via a process called evanescence, where the strength of a wave decays with height but is just about strong enough to still persist up into the stratosphere,” explains Fletcher. “We simply need to know more. It’s quite frustrating that we only discovered this stratospheric hexagon right at the end of Cassini’s lifespan.”
Understanding how and why Saturn’s north polar vortex has assumed a hexagonal shape will shed light on how phenomena deeper down in an atmosphere can influence the environment high up above, something that is of particular interest to scientists trying to figure out how energy is transported around in planetary atmospheres.
absrtact Saturn’s polar stratosphere exhibits the seasonal growth and dissipation of broad, warm vortices poleward of ~75° latitude, which are strongest in the summer and absent in winter. The longevity of the exploration of the Saturn system by Cassini allows the use of infrared spectroscopy to trace the formation of the North Polar Stratospheric Vortex (NPSV), a region of enhanced temperatures and elevated hydrocarbon abundances at millibar pressures. We constrain the timescales of stratospheric vortex formation and dissipation in both hemispheres. Although the NPSV formed during late northern spring, by the end of Cassini’s reconnaissance (shortly after northern summer solstice), it still did not display the contrasts in temperature and composition that were evident at the south pole during southern summer. The newly formed NPSV was bounded by a strengthening stratospheric thermal gradient near 78°N. The emergent boundary was hexagonal, suggesting that the Rossby wave responsible for Saturn’s long-lived polar hexagon—which was previously expected to be trapped in the troposphere—can influence the stratospheric temperatures some 300 km above Saturn’s clouds.
widespread hematite at high latitudes of the moon
shuai li et al. 2020
doi.org/10.1126/sciadv.aba1940
Iron is highly reactive with oxygen -- forming reddish rust commonly seen on Earth. The lunar surface and interior, however, are virtually devoid of oxygen, so pristine metallic iron is prevalent on the Moon and highly oxidized iron has not been confirmed in samples returned from the Apollo missions. In addition, hydrogen in solar wind blasts the lunar surface, which acts in opposition to oxidation. So, the presence of highly oxidized iron-bearing minerals, such as hematite, on the Moon is an unexpected discovery.
"Our hypothesis is that lunar hematite is formed through oxidation of lunar surface iron by the oxygen from the Earth's upper atmosphere that has been continuously blown to the lunar surface by solar wind when the Moon is in Earth's magnetotail during the past several billion years," said Li.
To make this discovery, Li, HIGP professor Paul Lucey and co-authors from NASA's Jet Propulsion Laboratory (JPL) and elsewhere analyzed the hyperspectral reflectance data acquired by the Moon Mineralogy Mapper (M3) designed by NASA JPL onboard India's Chandrayaan-1 mission.
This new research was inspired by Li's previous discovery of water ice in the Moon's polar regions in 2018.
"When I examined the M3 data at the polar regions, I found some spectral features and patterns are different from those we see at the lower latitudes or the Apollo samples," said Li. "I was curious whether it is possible that there are water-rock reactions on the Moon. After months investigation, I figured out I was seeing the signature of hematite."
The team found the locations where hematite is present are strongly correlated with water content at high latitude Li and others found previously and are more concentrated on the nearside, which always faces the Earth.
"More hematite on the lunar nearside suggested that it may be related to Earth," said Li. "This reminded me a discovery by the Japanese Kaguya mission that oxygen from the Earth's upper atmosphere can be blown to the lunar surface by solar wind when the Moon is in the Earth's magnetotail. So, Earth's atmospheric oxygen could be the major oxidant to produce hematite. Water and interplanetary dust impact may also have played critical roles"
"Interestingly, hematite is not absolutely absent from the far-side of the Moon where Earth's oxygen may have never reached, although much fewer exposures were seen," said Li. "The tiny amount of water (< ~0.1 wt.%) observed at lunar high latitudes may have been substantially involved in the hematite formation process on the lunar far-side, which has important implications for interpreting the observed hematite on some water poor S-type asteroids."
"This discovery will reshape our knowledge about the Moon's polar regions," said Li. "Earth may have played an important role on the evolution of the Moon's surface."
The research team hopes the NASA's ARTEMIS missions can return hematite samples from the polar regions. The chemical signatures of those samples can confirm their hypothesis whether the lunar hematite is oxidized by Earth's oxygen and may help reveal the evolution of the Earth's atmosphere in the past billions of years.
abstract Hematite (Fe2O3) is a common oxidization product on Earth, Mars, and some asteroids. Although oxidizing processes have been speculated to operate on the lunar surface and form ferric iron–bearing minerals, unambiguous detections of ferric minerals forming under highly reducing conditions on the Moon have remained elusive. Our analyses of the Moon Mineralogy Mapper data show that hematite, a ferric mineral, is present at high latitudes on the Moon, mostly associated with east- and equator-facing sides of topographic highs, and is more prevalent on the nearside than the farside. Oxygen delivered from Earth’s upper atmosphere could be the major oxidant that forms lunar hematite. Hematite at craters of different ages may have preserved the oxygen isotopes of Earth’s atmosphere in the past billions of years. Future oxygen isotope measurements can test our hypothesis and may help reveal the evolution of Earth’s atmosphere.
dark matter, dark energy
dynamical effects of the scale invariance of the empty space: the fall of dark matter?
andre maeder 2017
http://dx.doi.org/10.3847/1538-4357/aa92cc
a unifying theory of dark energy and dark matter: negative masses and matter creation within a modified λcdm framework
j. s. farnes 2018
http://dx.doi.org/10.1051/0004-6361/201832898
Our current, widely recognised model of the Universe, called LambdaCDM, tells us nothing about what dark matter and dark energy are like physically. We only know about them because of the gravitational effects they have on other, observable matter.
This new model, published today in Astronomy and Astrophysics, by Dr Jamie Farnes from the Oxford e-Research Centre, Department of Engineering Science, offers a new explanation. Dr Farnes says: "We now think that both dark matter and dark energy can be unified into a fluid which possesses a type of 'negative gravity', repelling all other material around them. Although this matter is peculiar to us, it suggests that our cosmos is symmetrical in both positive and negative qualities."
The existence of negative matter had previously been ruled out as it was thought this material would become less dense as the Universe expands, which runs contrary to our observations that show dark energy does not thin out over time. However, Dr Farnes' research applies a 'creation tensor', which allows for negative masses to be continuously created. It demonstrates that when more and more negative masses are continually bursting into existence, this negative mass fluid does not dilute during the expansion of the cosmos. In fact, the fluid appears to be identical to dark energy.
Dr Farnes's theory also provides the first correct predictions of the behaviour of dark matter halos. Most galaxies are rotating so rapidly they should be tearing themselves apart, which suggests that an invisible 'halo' of dark matter must be holding them together. The new research published today features a computer simulation of the properties of negative mass, which predicts the formation of dark matter halos just like the ones inferred by observations using modern radio telescopes.
Albert Einstein provided the first hint of the dark universe exactly 100 years ago, when he discovered a parameter in his equations known as the 'cosmological constant', which we now know to be synonymous with dark energy. Einstein famously called the cosmological constant his 'biggest blunder', although modern astrophysical observations prove that it is a real phenomenon. In notes dating back to 1918, Einstein described his cosmological constant, writing that "a modification of the theory is required such that 'empty space' takes the role of gravitating negative masses which are distributed all over the interstellar space." It is therefore possible that Einstein himself predicted a negative-mass-filled universe.
Dr Farnes says: "Previous approaches to combining dark energy and dark matter have attempted to modify Einstein's theory of general relativity, which has turned out to be incredibly challenging. This new approach takes two old ideas that are known to be compatible with Einstein's theory -- negative masses and matter creation -- and combines them together.
"The outcome seems rather beautiful: dark energy and dark matter can be unified into a single substance, with both effects being simply explainable as positive mass matter surfing on a sea of negative masses."
Proof of Dr Farnes's theory will come from tests performed with a cutting-edge radio telescope known as the Square Kilometre Array (SKA), an international endeavour to build the world's largest telescope in which the University of Oxford is collaborating.
Dr Farnes adds: "There are still many theoretical issues and computational simulations to work through, and LambdaCDM has a nearly 30 year head start, but I'm looking forward to seeing whether this new extended version of LambdaCDM can accurately match other observational evidence of our cosmology. If real, it would suggest that the missing 95% of the cosmos had an aesthetic solution: we had forgotten to include a simple minus sign."
abstract Dark energy and dark matter constitute 95% of the observable Universe. Yet the physical nature of these two phenomena remains a mystery. Einstein suggested a long-forgotten solution: gravitationally repulsive negative masses, which drive cosmic expansion and cannot coalesce into light-emitting structures. However, contemporary cosmological results are derived upon the reasonable assumption that the Universe only contains positive masses. By reconsidering this assumption, I have constructed a toy model which suggests that both dark phenomena can be unified into a single negative mass fluid. The model is a modified ΛCDM cosmology, and indicates that continuously-created negative masses can resemble the cosmological constant and can flatten the rotation curves of galaxies. The model leads to a cyclic universe with a time-variable Hubble parameter, potentially providing compatibility with the current tension that is emerging in cosmological measurements. In the first three-dimensional N-body simulations of negative mass matter in the scientific literature, this exotic material naturally forms haloes around galaxies that extend to several galactic radii. These haloes are not cuspy. The proposed cosmological model is therefore able to predict the observed distribution of dark matter in galaxies from first principles. The model makes several testable predictions and seems to have the potential to be consistent with observational evidence from distant supernovae, the cosmic microwave background, and galaxy clusters. These findings may imply that negative masses are a real and physical aspect of our Universe, or alternatively may imply the existence of a superseding theory that in some limit can be modelled by effective negative masses. Both cases lead to the surprising conclusion that the compelling puzzle of the dark Universe may have been due to a simple sign error.
radiation
hypothesis: muon radiation dose and marine megafaunal extinction at the end-pliocene supernova
adrian l. melott et al. 2018
http://dx.doi.org/10.1089/ast.2018.1902
inclined zenith aurora over kyoto on 17 september 1770: graphical evidence of extreme magnetic storm
ryuho kataoka, kiyomi iwahashi 2017
dx.doi.org/10.1002/2017SW001690
solar flares affecting radioactive decay
solar system exposure to supernova γ radiation
g. robert brakenridge 2020
doi.org/10.1017/s1473550420000348
impact
end of snowball earth?
precise radiometric age establishes yarrabubba, western australia, as earth’s oldest recognised meteorite impact structure
timmons m. erickson et al. 2020
http://dx.doi.org/10.1038/s41467-019-13985-7
zircon and monazite that were ‘shock recrystallized’ by the asteroid strike, at the base of the eroded crater to determine the exact age of Yarrabubba.
The team inferred that the impact may have occurred into an ice-covered landscape, vaporised a large volume of ice into the atmosphere, and produced a 70km diameter crater in the rocks beneath.
Professor Kirkland said the timing raised the possibility that the Earth’s oldest asteroid impact may have helped lift the planet out of a deep freeze.
“Yarrabubba, which sits between Sandstone and Meekatharra in central WA, had been recognised as an impact structure for many years, but its age wasn’t well determined,” Professor Kirkland said.
“Now we know the Yarrabubba crater was made right at the end of what’s commonly referred to as the early Snowball Earth — a time when the atmosphere and oceans were evolving and becoming more oxygenated and when rocks deposited on many continents recorded glacial conditions.”
Associate Professor Nicholas Timms noted the precise coincidence between the Yarrabubba impact and the disappearance of glacial deposits.
“The age of the Yarrabubba impact matches the demise of a series of ancient glaciations. After the impact, glacial deposits are absent in the rock record for 400 million years. This twist of fate suggests that the large meteorite impact may have influenced global climate,” Associate Professor Timms said.
“Numerical modelling further supports the connection between the effects of large impacts into ice and global climate change. Calculations indicated that an impact into an ice-covered continent could have sent half a trillion tons of water vapour — an important greenhouse gas — into the atmosphere. This finding raises the question whether this impact may have tipped the scales enough to end glacial conditions.”
abstract The ~70 km-diameter Yarrabubba impact structure in Western Australia is regarded as among Earth’s oldest, but has hitherto lacked precise age constraints. Here we present U–Pb ages for impact-driven shock-recrystallised accessory minerals. Shock-recrystallised monazite yields a precise impact age of 2229 ± 5 Ma, coeval with shock-reset zircon. This result establishes Yarrabubba as the oldest recognised meteorite impact structure on Earth, extending the terrestrial cratering record back >200 million years. The age of Yarrabubba coincides, within uncertainty, with temporal constraint for the youngest Palaeoproterozoic glacial deposits, the Rietfontein diamictite in South Africa. Numerical impact simulations indicate that a 70 km-diameter crater into a continental glacier could release between 8.7 × 1013 to 5.0 × 1015 kg of H2O vapour instantaneously into the atmosphere. These results provide new estimates of impact-produced H2O vapour abundances for models investigating termination of the Paleoproterozoic glaciations, and highlight the possible role of impact cratering in modifying Earth’s climate.
anomalous k-pg–aged seafloor attributed to impact-induced mid-ocean ridge magmatism
joseph s. byrnes and leif karlstrom 2018
http://dx.doi.org/10.1126/sciadv.aao2994
postimpact earliest paleogene warming shown by fish debris oxygen isotopes (el kef, tunisia)
k. g. macleod et al. 2018
http://dx.doi.org/10.1126/science.aap8525
a large impact crater beneath hiawatha glacier in northwest greenland
kurt h. kjær et al. 2018
http://dx.doi.org/10.1126/sciadv.aar8173
prelude to extinction: a seismically induced onshore surge deposit at the kpg boundary, north dakota
depalma et al. 2019
http://doi.org/10.1073/pnas.1817407116
tiny glass beads began to fall like birdshot from the heavens. The rain of glass was so heavy it may have set fire to much of the vegetation on land. In the water, fish struggled to breathe as the beads clogged their gills.
The heaving sea turned into a 30-foot wall of water when it reached the mouth of a river, tossing hundreds, if not thousands, of fresh-water fish -- sturgeon and paddlefish -- onto a sand bar and temporarily reversing the flow of the river. Stranded by the receding water, the fish were pelted by glass beads up to 5 millimeters in diameter, some burying themselves inches deep in the mud. The torrent of rocks, like fine sand, and small glass beads continued for another 10 to 20 minutes before a second large wave inundated the shore and covered the fish with gravel, sand and fine sediment, sealing them from the world for 66 million years.
This unique, fossilized graveyard -- fish stacked one atop another and mixed in with burned tree trunks, conifer branches, dead mammals, mosasaur bones, insects, the partial carcass of a Triceratops, marine microorganisms called dinoflagellates and snail-like marine cephalopods called ammonites -- was unearthed by paleontologist Robert DePalma over the past six years in the Hell Creek Formation, not far from Bowman, North Dakota. The evidence confirms a suspicion that nagged at DePalma in his first digging season during the summer of 2013 -- that this was a killing field laid down soon after the asteroid impact that eventually led to the extinction of all ground-dwelling dinosaurs. The impact at the end of the Cretaceous Period, the so-called K-T boundary, exterminated 75 percent of life on Earth.
"This is the first mass death assemblage of large organisms anyone has found associated with the K-T boundary," said DePalma, curator of paleontology at the Palm Beach Museum of Natural History in Florida and a doctoral student at the University of Kansas. "At no other K-T boundary section on Earth can you find such a collection consisting of a large number of species representing different ages of organisms and different stages of life, all of which died at the same time, on the same day."
In a paper to appear next week in the journal Proceedings of the National Academy of Sciences, he and his American and European colleagues, including two University of California, Berkeley, geologists, describe the site, dubbed Tanis, and the evidence connecting it with the asteroid or comet strike off Mexico's Yucatan Peninsula 66 million years ago. That impact created a huge crater, called Chicxulub, in the ocean floor and sent vaporized rock and cubic miles of asteroid dust into the atmosphere. The cloud eventually enveloped Earth, setting the stage for Earth's last mass extinction.
"It's like a museum of the end of the Cretaceous in a layer a meter-and-a-half thick," said Mark Richards, a UC Berkeley professor emeritus of earth and planetary science who is now provost and professor of earth and space sciences at the University of Washington.
Richards and Walter Alvarez, a UC Berkeley Professor of the Graduate School who 40 years ago first hypothesized that a comet or asteroid impact caused the mass extinction, were called in by DePalma and Dutch scientist Jan Smit to consult on the rain of glass beads and the tsunami-like waves that buried and preserved the fish. The beads, called tektites, formed in the atmosphere from rock melted by the impact.
Tsunami vs. seiche
Richards and Alvarez determined that the fish could not have been stranded and then buried by a typical tsunami, a single wave that would have reached this previously unknown arm of the Western Interior Seaway no less than 10 to 12 hours after the impact 3,000 kilometers away, if it didn't peter out before then. Their reasoning: The tektites would have rained down within 45 minutes to an hour of the impact, unable to create mudholes if the seabed had not already been exposed.
Instead, they argue, seismic waves likely arrived within 10 minutes of the impact from what would have been the equivalent of a magnitude 10 or 11 earthquake, creating a seiche (pronounced saysh), a standing wave, in the inland sea that is similar to water sloshing in a bathtub during an earthquake. Though large earthquakes often generate seiches in enclosed bodies of water, they're seldom noticed, Richards said. The 2011 Tohoku quake in Japan, a magnitude 9.0, created six-foot-high seiches 30 minutes later in a Norwegian fjord 8,000 kilometers away.
"The seismic waves start arising within nine to 10 minutes of the impact, so they had a chance to get the water sloshing before all the spherules (small spheres) had fallen out of the sky," Richards said. "These spherules coming in cratered the surface, making funnels -- you can see the deformed layers in what used to be soft mud -- and then rubble covered the spherules. No one has seen these funnels before."
The tektites would have come in on a ballistic trajectory from space, reaching terminal velocities of between 100 and 200 miles per hour, according to Alvarez, who estimated their travel time decades ago.
"You can imagine standing there being pelted by these glass spherules. They could have killed you," Richards said. Many believe that the rain of debris was so intense that the energy ignited wildfires over the entire American continent, if not around the world.
"Tsunamis from the Chicxulub impact are certainly well-documented, but no one knew how far something like that would go into an inland sea," DePalma said. "When Mark came aboard, he discovered a remarkable artifact -- that the incoming seismic waves from the impact site would have arrived at just about the same time as the atmospheric travel time of the ejecta. That was our big breakthrough."
At least two huge seiches inundated the land, perhaps 20 minutes apart, leaving six feet of deposits covering the fossils. Overlaying this is a layer of clay rich in iridium, a metal rare on Earth, but common in asteroids and comets. This layer is known as the K-T, or K-Pg boundary, marking the end of the Cretaceous Period and the beginning of the Tertiary Period, or Paleogene.
Iridium
In 1979, Alvarez and his father, Nobelist Luis Alvarez of UC Berkeley, were the first to recognize the significance of iridium that is found in 66 million-year-old rock layers around the world. They proposed that a comet or asteroid impact was responsible for both the iridium at the K-T boundary and the mass extinction.
The impact would have melted the bedrock under the seafloor and pulverized the asteroid, sending dust and melted rock into the stratosphere, where winds would have carried them around the planet and blotted out the sun for months, if not years. Debris would have rained down from the sky: not only tektites, but also rock debris from the continental crust, including shocked quartz, whose crystal structure was deformed by the impact.
The iridium-rich dust from the pulverized meteor would have been the last to fall out of the atmosphere after the impact, capping off the Cretaceous.
"When we proposed the impact hypothesis to explain the great extinction, it was based just on finding an anomalous concentration of iridium -- the fingerprint of an asteroid or comet," said Alvarez. "Since then, the evidence has gradually built up. But it never crossed my mind that we would find a deathbed like this."
Key confirmation of the meteor hypothesis was the discovery of a buried impact crater, Chicxulub, in the Caribbean and off the coast of the Yucatan in Mexico, that was dated to exactly the age of the extinction. Shocked quartz and glass spherules were also found in K-Pg layers worldwide. The new discovery at Tanis is the first time the debris produced in the impact was found along with animals killed in the immediate aftermath of the impact.
"And now we have this magnificent and completely unexpected site that Robert DePalma is excavating in North Dakota, which is so rich in detailed information about what happened as a result of the impact," Alvarez said. "For me, it is very exciting and gratifying!"
Tektites
Jan Smit, a retired professor of sedimentary geology from Vrije Universiteit in Amsterdam in The Netherlands who is considered the world expert on tektites from the impact, joined DePalma to analyze and date the tektites from the Tanis site. Many were found in near perfect condition embedded in amber, which at the time was pliable pine pitch.
"I went to the site in 2015 and, in front of my eyes, he (DePalma) uncovered a charred log or tree trunk about four meters long which was covered in amber, which acted as sort of an aerogel and caught the tektites when they were coming down," Smit said. "It was a major discovery, because the resin, the amber, covered the tektites completely, and they are the most unaltered tektites I have seen so far, not 1 percent of alteration. We dated them, and they came out to be exactly from the K-T boundary."
The tektites in the fishes' gills are also a first.
"Paddlefish swim through the water with their mouths open, gaping, and in this net, they catch tiny particles, food particles, in their gill rakers, and then they swallow, like a whale shark or a baleen whale," Smit said. "They also caught tektites. That by itself is an amazing fact. That means that the first direct victims of the impact are these accumulations of fishes."
Smit also noted that the buried body of a Triceratops and a duck-billed hadrosaur proves beyond a doubt that dinosaurs were still alive at the time of the impact.
"We have an amazing array of discoveries which will prove in the future to be even more valuable," Smit said. "We have fantastic deposits that need to be studied from all different viewpoints. And I think we can unravel the sequence of incoming ejecta from the Chicxulub impact in great detail, which we would never have been able to do with all the other deposits around the Gulf of Mexico."
The Chicxulub impact played a crucial role in the Cretaceous–Paleogene extinction. However the earliest postimpact effects, critical to fully decode the profound influence on Earth’s biota, are poorly understood due to a lack of high-temporal-resolution contemporaneous deposits. The Tanis site, which preserves a rapidly deposited, ejecta-bearing bed in the Hell Creek Formation, helps to resolve that long-standing deficit. Emplaced immediately (minutes to hours) after impact, Tanis provides a postimpact “snapshot,” including ejecta accretion and faunal mass death, advancing our understanding of the immediate effects of the Chicxulub impact. Moreover, we demonstrate that the depositional event, calculated to have coincided with the arrival of seismic waves from Chicxulub, likely resulted from a seismically coupled local seiche.
The most immediate effects of the terminal-Cretaceous Chicxulub impact, essential to understanding the global-scale environmental and biotic collapses that mark the Cretaceous–Paleogene extinction, are poorly resolved despite extensive previous work. Here, we help to resolve this by describing a rapidly emplaced, high-energy onshore surge deposit from the terrestrial Hell Creek Formation in Montana. Associated ejecta and a cap of iridium-rich impactite reveal that its emplacement coincided with the Chicxulub event. Acipenseriform fish, densely packed in the deposit, contain ejecta spherules in their gills and were buried by an inland-directed surge that inundated a deeply incised river channel before accretion of the fine-grained impactite. Although this deposit displays all of the physical characteristics of a tsunami runup, the timing (<1 hour postimpact) is instead consistent with the arrival of strong seismic waves from the magnitude Mw ∼10 to 11 earthquake generated by the Chicxulub impact, identifying a seismically coupled seiche inundation as the likely cause. Our findings present high-resolution chronology of the immediate aftereffects of the Chicxulub impact event in the Western Interior, and report an impact-triggered onshore mix of marine and terrestrial sedimentation—potentially a significant advancement for eventually resolving both the complex dynamics of debris ejection and the full nature and extent of biotic disruptions that took place in the first moments postimpact.
accelerated diversifications in three diverse families of morphologically complex lichen-forming fungi link to major historical events
jen-pan huang et al. 2019
http://dx.doi.org/10.1038/s41598-019-44881-1
"We thought that lichens would be affected negatively, but in the three groups we looked at, they seized the chance and diversified rapidly," says Jen-Pang Huang, the paper's first author, a former postdoctoral researcher at the Field Museum now at Academia Sinica in Taipei. "Some lichens grow sophisticated 3D structures like plant leaves, and these ones filled the niches of plants that died out."
The researchers got interested in studying the effects of the mass extinction on lichens after reading a paper about how the asteroid strike also caused many species of early birds to go extinct. "I read it on the train, and I thought, 'My god, the poor lichens, they must have suffered too, how can we trace what happened to them?'" says Thorsten Lumbsch, senior author on the study and the Field Museum's curator of lichenized fungi.
You've seen lichens a million times, even if you didn't realize it. "Lichens are everywhere," says Huang. "If you go on a walk in the city, the rough spots or gray spots you see on rocks or walls or trees, those are common crust lichens. On the ground, they sometimes look like chewing gum. And if you go into a more pristine forest, you can find orange, yellow, and vivid violet colors -- lichens are really pretty." They're what scientists call "symbiotic organisms" -- they're made up of two different life forms sharing one body and working together. They're a partnership between a fungus and an organism that can perform photosynthesis, making energy from sunlight -- either a tiny algae plant, or a special kind of blue-green bacterium. Fungi, which include mushrooms and molds, are on their own branch on the tree of life, separate from plants and animals (and actually more closely related to us than to plants). The main role of fungi is to break down decomposing material.
During the mass extinction 66 million years ago, plants suffered since ash from the asteroid blocked out sunlight and lowered temperatures. But the mass extinction seemed to be a good thing for fungi -- they don't rely on sunlight for food and just need lots of dead stuff, and the fossil record shows an increase in fungal spores at this time. Since lichens contain a plant and a fungus, scientists wondered whether they were affected negatively like a plant or positively like a fungus.
"We originally expected lichens to be affected in a negative way, since they contain green things that need light," says Huang.
To see how lichens were affected by the mass extinction, the scientists had to get creative -- there aren't many fossil lichens from that time frame. But while the researchers didn't have lichen fossils, they did have lots of modern lichen DNA.
From observing fungi growing in lab settings, scientists know generally how often genetic mutations show up in fungal DNA -- how frequently a letter in the DNA sequence accidentally gets switched during the DNA copying process. That's called the mutation rate. And if you know the mutation rate, if you compare the DNA sequences of two different species, you can generally extrapolate how long ago they must have had a common ancestor with the same DNA.
The researchers fed DNA sequences of three families of lichens into a software program that compared their DNA and figured out what their family tree must look like, including estimates of how long ago it branched into the groups we see today. They bolstered this information with the few lichen fossils they did have, from 100 and 400 million years ago. And the results pointed to a lichen boom after 66 million years ago, at least for some of the leafier lichen families.
"Some groups don't show a change, so they didn't suffer or benefit from the changes to the environment," says Lumbsch, who in addition to his work on lichens is the Vice President of Science and Education at the Field. "Some lichens went extinct, and the leafy macrolichens filled those niches. I was really happy when I saw that not all the lichens suffered."
The results underline how profoundly the natural world we know today was shaped by this mass extinction. "If you could go back 40 million years, the most prominent groups in vegetation, birds, fungi -- they'd be more similar to what you see now than what you'd see 70 million years ago," says Lumbsch. "Most of what we see around us nowadays in nature originated after the dinosaurs."
abstract Historical mass extinction events had major impacts on biodiversity patterns. The most recent and intensively studied event is the Cretaceous – Paleogene (K-Pg) boundary (ca. 66 million years ago [MYA]). However, the factors that may have impacted diversification dynamics vary across lineages. We investigated the macroevolutionary dynamics with a specific focus on the impact of major historical events such as the K-Pg mass extinction event on two major subclasses – Lecanoromycetidae and Ostropomycetidae – of lichen-forming fungi and tested whether variation in the rate of diversification can be associated with the evolution of a specific trait state - macrolichen. Our results reveal accelerated diversification events in three families of morphologically complex lichen-forming fungi – Cladoniaceae, Parmeliaceae, and Peltigeraceae – which are from the subclass Lecanoromycetidae and mostly composed of macrolichens, those that form three dimensional structures. Our RTT plot result for the subclass Lecanoromycetidae also reveals accelerated diversification. Changes in diversification rates occurred around the transition between Mesozoic and Cenozoic eras and was likely related to the K-Pg mass extinction event. The phylogenetic positions for rate increases estimated based on marginal shift probability are, however, scattered from 100 to 40 MYA preventing us from making explicit inference. Although we reveal that the phenotypic state of macrolichens is associated with a higher diversification rate than microlichens, we also show that the evolution of macrolichens predated the K-Pg event. Furthermore, the association between macrolichens and increased diversification is not universal and can be explained, in part, by phylogenetic relatedness. By investigating the macroevolutionary dynamics of lichen-forming fungi our study provides a new empirical system suitable to test the effect of major historical event on shaping biodiversity patterns and to investigate why changes in biodiversity patterns are not in concordance across clades. Our results imply that multiple historical events during the transition from Mesozoic to Cenozoic eras, including the K-Pg mass extinction event, impacted the evolutionary dynamics in lichen-forming fungi. However, future studies focusing on individual lichen-forming fungal families are required to ascertain whether diversification rates are associated with growth form and certain geological events.
sediment cores from white pond, south carolina, contain a platinum anomaly, pyrogenic carbon peak, and coprophilous spore decline at 12.8 ka
christopher r. moore et al. 2019
http://dx.doi.org/10.1038/s41598-019-51552-8
further evidence of a cosmic impact based on research done at White Pond near Elgin, South Carolina. The study builds on similar findings of platinum spikes -- an element associated with cosmic objects like asteroids or comets -- in North America, Europe, western Asia and recently in Chile and South Africa.
"We continue to find evidence and expand geographically. There have been numerous papers that have come out in the past couple of years with similar data from other sites that almost universally support the notion that there was an extraterrestrial impact or comet airburst that caused the Younger Dryas climate event," Moore says.
Moore also was lead author on a previous paper documenting sites in North America where platinum spikes have been found and a co-author on several other papers that document elevated levels of platinum in archaeological sites, including Pilauco, Chile -- the first discovery of evidence in the Southern Hemisphere.
"First, we thought it was a North American event, and then there was evidence in Europe and elsewhere that it was a Northern Hemisphere event. And now with the research in Chile and South Africa, it looks like it was probably a global event," he says.
In addition, a team of researchers found unusually high concentrations of platinum and iridium in outwash sediments from a recently discovered crater in Greenland that could have been the impact point. Although the crater hasn't been precisely dated yet, Moore says the possibility is good that it could be the "smoking gun" that scientists have been looking for to confirm a cosmic event. Additionally, data from South America and elsewhere suggests the event may have actually included multiple impacts and airbursts over the entire globe.
While the brief return to ice-age conditions during the Younger Dryas period has been well-documented, the reasons for it and the decline of human populations and animals have remained unclear. The impact hypothesis was proposed as a possible trigger for these abrupt climate changes that lasted about 1,400 years.
The Younger Dryas event gets its name from a wildflower, Dryas octopetala, which can tolerate cold conditions and suddenly became common in parts of Europe 12,800 years ago. The Younger Dryas Impact Hypothesis became controversial, Moore says, because the all-encompassing theory that a cosmic impact triggered cascading events leading to extinctions was viewed as improbable by some scientists.
"It was bold in the sense that it was trying to answer a lot of really tough questions that people have been grappling with for a long time in a single blow," he says, adding that some researchers continue to be critical.
The conventional view has been that the failure of glacial ice dams allowed a massive release of freshwater into the north Atlantic, affecting oceanic circulation and causing the Earth to plunge into a cold climate. The Younger Dryas hypothesis simply claims that the cosmic impact was the trigger for the meltwater pulse into the oceans.
In research at White Pond in South Carolina, Moore and his colleagues used a core barrel to extract sediment samples from underneath the pond. The samples, dated to the beginning of the Younger Dryas with radiocarbon, contain a large platinum anomaly, consistent with findings from other sites, Moore says. A large soot anomaly also was found in cores from the site, indicating regional large-scale wildfires in the same time interval.
In addition, fungal spores associated with the dung of large herbivores were found to decrease at the beginning of the Younger Dryas period, suggesting a decline in ice-age megafauna beginning at the time of the impact.
"We speculate that the impact contributed to the extinction, but it wasn't the only cause. Over hunting by humans almost certainly contributed, too, as did climate change," Moore says. "Some of these animals survived after the event, in some cases for centuries. But from the spore data at White Pond and elsewhere, it looks like some of them went extinct at the beginning of the Younger Dryas, probably as a result of the environmental disruption caused by impact-related wildfires and climate change."
Additional evidence found at other sites in support of an extraterrestrial impact includes the discovery of meltglass, microscopic spherical particles and nanodiamonds, indicating enough heat and pressure was present to fuse materials on the Earth's surface. Another indicator is the presence of iridium
abstract A widespread platinum (Pt) anomaly was recently documented in Greenland ice and 11 North American sedimentary sequences at the onset of the Younger Dryas (YD) event (~12,800 cal yr BP), consistent with the YD Impact Hypothesis. We report high-resolution analyses of a 1-meter section of a lake core from White Pond, South Carolina, USA. After developing a Bayesian age-depth model that brackets the late Pleistocene through early Holocene, we analyzed and quantified the following: (1) Pt and palladium (Pd) abundance, (2) geochemistry of 58 elements, (3) coprophilous spores, (4) sedimentary organic matter (OC and sedaDNA), (5) stable isotopes of C (δ13C) and N (δ15N), (6) soot, (7) aciniform carbon, (8) cryptotephra, (9) mercury (Hg), and (10) magnetic susceptibility. We identified large Pt and Pt/Pd anomalies within a 2-cm section dated to the YD onset (12,785 ± 58 cal yr BP). These anomalies precede a decline in coprophilous spores and correlate with an abrupt peak in soot and C/OC ratios, indicative of large-scale regional biomass burning. We also observed a relatively large excursion in δ15N values, indicating rapid climatic and environmental/hydrological changes at the YD onset. Our results are consistent with the YD Impact Hypothesis and impact-related environmental and ecological changes.
ice age, snowball earth
an extraterrestrial trigger for the mid-ordovician ice age: dust from the breakup of the l-chondrite parent body
birger schmitz et al. 2019
http://dx.doi.org/10.1126/sciadv.aax4184
when a 93-mile-wide asteroid between Mars and Jupiter broke apart 466 million years ago, it created way more dust than usual. "Normally, Earth gains about 40,000 tons of extraterrestrial material every year," says Philipp Heck, a curator at the Field Museum, associate professor at the University of Chicago, and one of the paper's authors. "Imagine multiplying that by a factor of a thousand or ten thousand." To contextualize that, in a typical year, one thousand semi trucks' worth of interplanetary dust fall to Earth. In the couple million years following the collision, it'd be more like ten million semis.
"Our hypothesis is that the large amounts of extraterrestrial dust over a timeframe of at least two million years played an important role in changing the climate on Earth, contributing to cooling," says Heck.
"Our results show for the first time that such dust, at times, has cooled Earth dramatically," says Birger Schmitz of Sweden's Lund University, the study's lead author and a research associate at the Field Museum. "Our studies can give a more detailed, empirical-based understanding of how this works, and this in turn can be used to evaluate if model simulations are realistic."
To figure it out, researchers looked for traces of space dust in 466-million-year-old rocks, and compared it to tiny micrometeorites from Antarctica as a reference. "We studied extraterrestrial matter, meteorites and micrometeorites, in the sedimentary record of Earth, meaning rocks that were once sea floor," says Heck. "And then we extracted the extraterrestrial matter to discover what it was and where it came from."
Extracting the extraterrestrial matter -- the tiny meteorites and bits of dust from outer space -- involves taking the ancient rock and treating it with acid that eats away the stone and leaves the space stuff. The team then analyzed the chemical makeup of the remaining dust. The team also analyzed rocks from the ancient seafloor and looked for elements that rarely appear in Earth rocks and for isotopes -- different forms of atoms -- that show hallmarks of coming from outer space. For instance, helium atoms normally have two protons, two neutrons, and two electrons, but some that are shot out of the Sun and into space are missing a neutron. The presence of these special helium isotopes, along with rare metals often found in asteroids, proves that the dust originated from space.
Other scientists had already established that our planet was undergoing an ice age around this time. The amount of water in the Earth's oceans influences the way that rocks on the seabed form, and the rocks from this time period show signs of shallower oceans -- a hint that some of the Earth's water was trapped in glaciers and sea ice. Schmitz and his colleagues are the first to show that this ice age syncs up with the extra dust in the atmosphere. "The timing appears to be perfect," he says. The extra dust in the atmosphere helps explain the ice age -- by filtering out sunlight, the dust would have caused global cooling.
Since the dust floated down to Earth over at least two million years, the cooling was gradual enough for life to adapt and even benefit from the changes. An explosion of new species evolved as creatures adapted for survival in regions with different temperatures.
Heck notes that while this period of global cooling proved beneficial to life on Earth, fast-paced climate change can be catastrophic. "In the global cooling we studied, we're talking about timescales of millions of years. It's very different from the climate change caused by the meteorite 65 million years ago that killed the dinosaurs, and it's different from the global warming today -- this global cooling was a gentle nudge. There was less stress."
abstract The breakup of the L-chondrite parent body in the asteroid belt 466 million years (Ma) ago still delivers almost a third of all meteorites falling on Earth. Our new extraterrestrial chromite and 3He data for Ordovician sediments show that the breakup took place just at the onset of a major, eustatic sea level fall previously attributed to an Ordovician ice age. Shortly after the breakup, the flux to Earth of the most fine-grained, extraterrestrial material increased by three to four orders of magnitude. In the present stratosphere, extraterrestrial dust represents 1% of all the dust and has no climatic significance. Extraordinary amounts of dust in the entire inner solar system during >2 Ma following the L-chondrite breakup cooled Earth and triggered Ordovician icehouse conditions, sea level fall, and major faunal turnovers related to the Great Ordovician Biodiversification Event.
arc-continent collisions in the tropics set earth’s climate state
francis a. macdonald et al. 2019
http://dx.doi.org/10.1126/science.aav5300
each of the last three major ice ages were preceded by tropical "arc-continent collisions" -- tectonic pileups that occurred near the Earth's equator, in which oceanic plates rode up over continental plates, exposing tens of thousands of kilometers of oceanic rock to a tropical environment.
The scientists say that the heat and humidity of the tropics likely triggered a chemical reaction between the rocks and the atmosphere. Specifically, the rocks' calcium and magnesium reacted with atmospheric carbon dioxide, pulling the gas out of the atmosphere and permanently sequestering it in the form of carbonates such as limestone.
Over time, the researchers say, this weathering process, occurring over millions of square kilometers, could pull enough carbon dioxide out of the atmosphere to cool temperatures globally and ultimately set off an ice age.
"We think that arc-continent collisions at low latitudes are the trigger for global cooling," says Oliver Jagoutz, an associate professor in MIT's Department of Earth, Atmospheric, and Planetary Sciences. "This could occur over 1-5 million square kilometers, which sounds like a lot. But in reality, it's a very thin strip of Earth, sitting in the right location, that can change the global climate."
Jagoutz' co-authors are Francis Macdonald and Lorraine Lisiecki of UC Santa Barbara, and Nicholas Swanson-Hysell and Yuem Park of UC Berkeley.
A tropical trigger
When an oceanic plate pushes up against a continental plate, the collision typically creates a mountain range of newly exposed rock. The fault zone along which the oceanic and continental plates collide is called a "suture." Today, certain mountain ranges such as the Himalayas contain sutures that have migrated from their original collision points, as continents have shifted over millenia.
In 2016, Jagoutz and his colleagues retraced the movements of two sutures that today make up the Himalayas. They found that both sutures stemmed from the same tectonic migration. Eighty million years ago, as the supercontinent known as Gondwana moved north, part of the landmass was crushed against Eurasia, exposing a long line of oceanic rock and creating the first suture; 50 million years ago, another collision between the supercontinents created a second suture.
The team found that both collisions occurred in tropical zones near the equator, and both preceded global atmospheric cooling events by several million years -- which is nearly instantaneous on a geologic timescale. After looking into the rates at which exposed oceanic rock, also known as ophiolites, could react with carbon dioxide in the tropics, the researchers concluded that, given their location and magnitude, both sutures could have indeed sequestered enough carbon dioxide to cool the atmosphere and trigger both ice ages.
Interestingly, they found that this process was likely responsible for ending both ice ages as well. Over millions of years, the oceanic rock that was available to react with the atmosphere eventually eroded away, replaced with new rock that took up far less carbon dioxide.
"We showed that this process can start and end glaciation," Jagoutz says. "Then we wondered, how often does that work? If our hypothesis is correct, we should find that for every time there's a cooling event, there are a lot of sutures in the tropics."
Exposing Earth's sutures
The researchers looked to see whether ice ages even further back in Earth's history were associated with similar arc-continent collisions in the tropics. They performed an extensive literature search to compile the locations of all the major suture zones on Earth today, and then used a computer simulation of plate tectonics to reconstruct the movement of these suture zones, and the Earth's continental and oceanic plates, back through time. In this way, they were able to pinpoint approximately where and when each suture originally formed, and how long each suture stretched.
They identified three periods over the last 540 million years in which major sutures, of about 10,000 kilometers in length, were formed in the tropics. Each of these periods coincided with each of three major, well-known ice ages, in the Late Ordovician (455 to 440 million years ago), the Permo-Carboniferous (335 to 280 million years ago), and the Cenozoic (35 million years ago to present day). Importantly, they found there were no ice ages or glaciation events during periods when major suture zones formed outside of the tropics.
"We found that every time there was a peak in the suture zone in the tropics, there was a glaciation event," Jagoutz says. "So every time you get, say, 10,000 kilometers of sutures in the tropics, you get an ice age."
He notes that a major suture zone, spanning about 10,000 kilometers, is still active today in Indonesia, and is possibly responsible for the Earth's current glacial period and the appearance of extensive ice sheets at the poles.
This tropical zone includes some of the largest ophiolite bodies in the world and is currently one of the most efficient regions on Earth for absorbing and sequestering carbon dioxide. As global temperatures are climbing as a result of human-derived carbon dioxide, some scientists have proposed grinding up vast quantities of ophiolites and spreading the minerals throughout the equatorial belt, in an effort to speed up this natural cooling process.
But Jagoutz says the act of grinding up and transporting these materials could produce additional, unintended carbon emissions. And it's unclear whether such measures could make any significant impact within our lifetimes.
"It's a challenge to make this process work on human timescales," Jagoutz says. "The Earth does this in a slow, geological process that has nothing to do with what we do to the Earth today. And it will neither harm us, nor save us."
abstract On multi-million-year timescales, Earth has experienced warm ice-free and cold glacial climates, but it is unknown if transitions between these background climate states were the result of changes in CO2 sources or sinks. Low-latitude arc-continent collisions are hypothesized to drive cooling by uplifting and eroding mafic and ultramafic rocks in the warm, wet tropics, thereby increasing Earth’s potential to sequester carbon through chemical weathering. To better constrain global weatherability through time, the paleogeographic position of all major Phanerozoic arc-continent collisions was reconstructed and compared to the latitudinal distribution of ice-sheets. This analysis reveals a strong correlation between the extent of glaciation and arc-continent collisions in the tropics. Earth’s climate state is set primarily by global weatherability, which changes with the latitudinal distribution of arc-continent collisions.
reduced continental weathering and marine calcification linked to late neogene decline in atmospheric co2
weimin si & yair rosenthal 2019
http://dx.doi.org/10.1038/s41561-019-0450-3
"If the cooling is not due to enhanced Himalayan rock weathering, then what processes have been overlooked?"
For decades, the leading hypothesis has been that the collision of the Indian and Asian continents and uplifting of the Himalayas brought fresh rocks to the Earth's surface, making them more vulnerable to weathering that captured and stored carbon dioxide -- a key greenhouse gas. But that hypothesis remains unconfirmed.
Lead author Weimin Si, a former Rutgers doctoral student now at Brown University, and Rosenthal challenge the hypothesis and examined deep-sea sediments rich with calcium carbonate.
Over millions of years, the weathering of rocks captured carbon dioxide and rivers carried it to the ocean as dissolved inorganic carbon, which is used by algae to build their calcium carbonate shells. When algae die, their skeletons fall on the seafloor and get buried, locking carbon from the atmosphere in deep-sea sediments.
If weathering increases, the accumulation of calcium carbonate in the deep sea should increase. But after studying dozens of deep-sea sediment cores through an international ocean drilling program, Si found that calcium carbonate in shells decreased significantly over 15 million years, which suggests that rock weathering may not be responsible for the long-term cooling.
Meanwhile, the scientists -- surprisingly -- also found that algae called coccolithophores adapted to the carbon dioxide decline over 15 million years by reducing their production of calcium carbonate. This reduction apparently was not taken into account in previous studies.
Many scientists believe that ocean acidification from high carbon dioxide levels will reduce the calcium carbonate in algae, especially in the near future. The data, however, suggest the opposite occurred over the 15 million years before the current global warming spell.
Rosenthal's lab is now trying to answer these questions by studying the evolution of calcium and other elements in the ocean.
abstract The globally averaged calcite compensation depth has deepened by several hundred metres in the past 15 Myr. This deepening has previously been interpreted to reflect increased alkalinity supply to the ocean driven by enhanced continental weathering due to the Himalayan orogeny during the late Neogene period. Here we examine mass accumulation rates of the main marine calcifying groups and show that global accumulation of pelagic carbonates has decreased from the late Miocene epoch to the late Pleistocene epoch even though CaCO3 preservation has improved, suggesting a decrease in weathering alkalinity input to the ocean, thus opposing expectations from the Himalayan uplift hypothesis. Instead, changes in relative contributions of coccoliths and planktonic foraminifera to the pelagic carbonates in relative shallow sites, where dissolution has not taken its toll, suggest that coccolith production in the euphotic zone decreased concomitantly with the reduction in weathering alkalinity inputs as registered by the decline in pelagic carbonate accumulation. Our work highlights a mechanism whereby, in addition to deep-sea dissolution, changes in marine calcification acted to modulate carbonate compensation in response to reduced weathering linked to the late Neogene cooling and decline in atmospheric partial pressure of carbon dioxide.
deep atlantic ocean carbon storage and the rise of 100,000-year glacial cycles
j. r. farmer et al. 2019
http://dx.doi.org/10.1038/s41561-019-0334-6
A million years ago, a longtime pattern of alternating glaciations and warm periods dramatically changed, when ice ages suddenly became longer and more intense. Scientists have long suspected that this was connected to the slowdown of a key Atlantic Ocean current system that today once again is slowing.
A new study of sediments from the Atlantic bottom directly links this slowdown with a massive buildup of carbon dragged from the air into the abyss. With the system running at full speed, this carbon would have percolated back into the air fairly quickly, but during this period it just stagnated in the depths. This suggests that the carbon drawdown cooled the planet -- the opposite of the greenhouse effect we are seeing now, as humans pump carbon into the atmosphere. But if the current keeps slowing now, we should not expect it to help us out by storing our emissions; possibly to the contrary. The study, led by researchers at Columbia University's Lamont-Doherty Earth Observatory, appears this week in the journal Nature Geoscience.
The scientists targeted a system of currents called the Atlantic meridional overturning circulation, or AMOC. Flowing northward near the surface, it transports warm, salty water from near the equator into the latitudes near Greenland and northern Europe. Here, it hits colder water from the Arctic, becomes denser and sinks into the abyss, taking with it large amounts of carbon absorbed from the atmosphere. The deep water then circles back south, where much of it re-merges in the Southern Ocean, to release carbon back to the air. The journey takes place over decades to centuries.
A 2014 study by Lamont-Doherty geochemist Steven Goldstein and his then student Leopoldo Pena-both of whom also are coauthors of the new study-showed that this current abruptly slowed around 950,000 years ago. The new study shows that this slowdown correlated directly with a huge buildup of carbon in the deep Atlantic, and corresponding decline of carbon in the air. This event was the apparent trigger for a series of ice ages that came every 100,000 years, versus previous ones that occurred about every 40,000 years, and which built up less ice than those that came later. Scientists call this turning point the Mid-Pleistocene Transition, and the new pattern has persisted right through the last ice age, which ended about 15,000 years ago. Exactly why the pattern has continued no one knows, but the study clearly demonstrates that the carbon missing from the air ended up in the ocean, and had a powerful effect on climate.
"It's a one-to-one relationship. It was like flipping a switch," said lead author Jesse Farmer, who did the work while a PhD. student at Lamont-Doherty. "It shows us that there's an intimate relationship between the amount of carbon stored in the ocean, and what the climate is doing."
The researchers reached their findings by analyzing cores of deep-sea sediments taken in the south and north Atlantic, where ancient deep waters passed by and left chemical clues about their contents in the shells of microscopic creatures. Their analysis confirmed the 2014 study showing that the AMOC weakened to an extent not seen before, around 950,000 years ago, and for an unusually long time. Because of this, the deep water collected about 50 billion tons more carbon than it had during previous glaciations -- equivalent to about one third of the human emissions that all the world's oceans have so far absorbed today. (For context, the oceans today absorb roughly a quarter of what we emit; land and vegetation take up a third. The rest stays in the air.)
In the warm period leading up to this event, the atmosphere had held about 280 parts per million carbon; with the slowdown, airborne carbon dioxide went down to 180 ppm, as measured by ice cores. Atmospheric carbon had sunk during previous glaciations as well, but from 280 ppm down only to about 210 ppm. (Because of human emissions during the past two centuries, this normal repeating 280 ppm warm-era figure has become obsolete; atmospheric carbon is now up to about 410 ppm.)
At some point, the current woke up again, and things warmed for a while before dropping back into another similarly extreme ice age, after 100,000 years. "There are lots of ideas about what caused these changes to happen, but it's hard to say what the trigger was," said Bärbel Hönisch, Farmer's advisor and coauthor of the study. "There are several different screws you could imagine turning, and lots of loose screws."
One idea, espoused by Goldstein's group among others: In the north, repeated build-ups of glaciers ultimately scrape everything on land down to bedrock. Subsequent glaciers are then able to stick fast to the bedrock and bulk up even more, before discharging icebergs into the ocean. This introduces more freshwater to mix with the AMOC, making it less dense and eventually unable to sink. On the other end, ice would also grow in Antarctica and discharge more icebergs, which would make the ocean waters colder and less salty, thus encouraging the growth of more sea ice. This, theoretically, would cap the surface and keep deep water from rising and releasing its carbon. But if this is indeed the way it works, it is not clear what starts or ends any of the processes; it is a chicken-and-egg kind of question.
The strength of the AMOC is believed to fluctuate naturally, but it appears to have weakened by an unusual 15 percent since the mid-20th century. No one is sure what is behind that, or what effects it might produce if the slowdown continues. Another Lamont-Doherty study last month showed that a slowdown around 13,000 years ago, at the tail end of the last ice age, was followed 400 years later by an intense cold snap that lasted centuries.
"We have to be careful about drawing parallels with that," said Farmer, now a postdoctoral researcher at Princeton University. "We see a similar weakening today, and one might say, 'Great! Ocean circulation is going to save us from warming climate!' But that's not correct, because of the way different parts of the climate system talk to each other." Farmer said that if the AMOC continues weakening now, it is probable that less carbon-laden water will sink in the north, at the same time, in the Southern Ocean, any carbon already arriving in the deep water will likely keep bubbling up without any problem. The result: carbon will continue to build in the air, not the ocean.
The researchers point out that the AMOC is only part of a much larger system of global circulation that connects all the oceans -- the so-called Great Ocean Conveyor, a term coined by the late Lamont-Doherty scientist Wallace Broecker, who laid the groundwork for much of the current research. Much less is known about the carbon dynamics of the Indian and Pacific, which together dwarf the Atlantic, so there are many missing pieces to the puzzle. Ongoing research at Lamont-Doherty is aimed at building carbon chronologies of those other waters in the next few years.
abstract Over the past three million years, Earth’s climate oscillated between warmer interglacials with reduced terrestrial ice volume and cooler glacials with expanded polar ice sheets. These climate cycles, as reflected in benthic foraminiferal oxygen isotopes, transitioned from dominantly 41-kyr to 100-kyr periodicities during the mid-Pleistocene 1,250 to 700 kyr ago (ka). Because orbital forcing did not shift at this time, the ultimate cause of this mid-Pleistocene transition remains enigmatic. Here we present foraminiferal trace element (B/Ca, Cd/Ca) and Nd isotope data that demonstrate a close linkage between Atlantic Ocean meridional overturning circulation and deep ocean carbon storage across the mid-Pleistocene transition. Specifically, between 950 and 900 ka, carbonate ion saturation decreased by 30 µmol kg−1 and phosphate concentration increased by 0.5 µmol kg−1 coincident with a 20% reduction of North Atlantic Deep Water contribution to the abyssal South Atlantic. These results demonstrate that the glacial deep Atlantic carbon inventory increased by approximately 50 Gt during the transition to 100-kyr glacial cycles. We suggest that the coincidence of our observations with evidence for increased terrestrial ice volume reflects how weaker overturning circulation and Southern Ocean biogeochemical feedbacks facilitated deep ocean carbon storage, which lowered the atmospheric partial pressure of CO2 and thereby enabled expanded terrestrial ice volume at the mid-Pleistocene transition.
initiation of snowball earth with volcanic sulfur aerosol emissions
f. a. macdonald & r. wordsworth 2017
dx.doi.org/10.1002/2016GL072335
the “dirty ice” of the mcmurdo ice shelf: analogues for biological oases during the cryogenian
i. hawes et al. 2018
https://doi.org/10.1111/gbi.12280
bisnorgammacerane traces predatory pressure and the persistent rise of algal ecosystems after snowball earth
lennart m. van maldegem et al. 2019
http://dx.doi.org/10.1038/s41467-019-08306-x
"All higher animal life forms, including us humans, produce cholesterol. Algae and bacteria produce their own characteristic fat molecules," says first author Lennart van Maldegem from Max Planck Institute (MPI) for Biogeochemistry, who recently moved to the Australian National University in Canberra, Australia. "Such fat molecules can survive in rocks for millions of years, as the oldest (chemical) remnants of organisms, and tell us now what type of life thrived in the former oceans long ago."
But the fossil fats the researchers recently discovered in Brazilian rocks, deposited just after the last Snowball glaciation, were not what they suspected. "Absolutely not," says team-leader Christian Hallmann from MPI for Biogeochemistry. "We were completely puzzled, because these molecules looked quite different from what we've ever seen before!"
Using sophisticated separation techniques, the team managed to purify minuscule amounts of the mysterious molecule and identify its structure by nuclear magnetic resonance in the NMR department of Christian Griesinger at Max Planck Institute for Biophysical Chemistry. "This is highly remarkable itself," according to Klaus Wolkenstein from MPI for Biophysical Chemistry and the Geoscience Centre of the University of Göttingen. "Never has a structure been elucidated with such a small amount of such an old molecule." The structure was chemically identified as 25,28-bisnorgammacerane -- abbreviated as BNG, as van Maldegem suggests.
Fossil fats most likely from heterotropic plankton
Yet the origin of the compound remained enigmatic. "We of course looked if we could find it elsewhere," says van Maldegem, who then studied hundreds of ancient rock samples, with rather surprising success. "In particular the Grand Canyon rocks really were an eye-opener," says Hallmann. Although nowadays mostly sweltering hot, these rocks had also been buried under kilometres of glacial ice around 700 million years ago. Detailed additional analyses of molecules in Grand Canyon rocks -- including presumed BNG-precursors, the distribution of steroids and stable carbon isotopic patterns -- led the authors to conclude that the new BNG molecule most likely derives from heterotrophic plankton, marine microbes that rely on consuming other organisms for gaining energy. "Unlike for example green algae that engage in photosynthesis and thus belong to autotrophic organisms, these heterotrophic microorganisms were true predators that gained energy by hunting and devouring other algae and bacteria," according to van Maldegem.
Predatory species create room for algae and other plankton
While predation is common amongst plankton in modern oceans, the discovery that it was so prominent 635 million years ago, exactly after the Snowball Earth glaciation, is a big deal for the science community. "Parallel to the occurrence of the enigmatic BNG molecule we observe the transition from a world whose oceans contained virtually only bacteria, to a more modern Earth system containing many more algae. We think that massive predation helped to 'clear' out the bacteria-dominated oceans and make space for algae," says van Maldegem. The resulting more complex feeding networks provided the dietary requirements for larger, more intricate lifeforms to evolve -- including the lineages that all animals, and eventually we humans, derive from. The massive onset of predation probably played a crucial role in the transformation of our planet and its ecosystems to its present state.
abstract Eukaryotic algae rose to ecological relevance after the Neoproterozoic Snowball Earth glaciations, but the causes for this consequential evolutionary transition remain enigmatic. Cap carbonates were globally deposited directly after these glaciations, but they are usually organic barren or thermally overprinted. Here we show that uniquely-preserved cap dolostones of the Araras Group contain exceptional abundances of a newly identified biomarker: 25,28-bisnorgammacerane. Its secular occurrence, carbon isotope systematics and co-occurrence with other demethylated terpenoids suggest a mechanistic connection to extensive microbial degradation of ciliate-derived biomass in bacterially dominated ecosystems. Declining 25,28-bisnorgammacerane concentrations, and a parallel rise of steranes over hopanes, indicate the transition from a bacterial to eukaryotic dominated ecosystem after the Marinoan deglaciation. Nutrient levels already increased during the Cryogenian and were a prerequisite, but not the ultimate driver for the algal rise. Intense predatory pressure by bacterivorous protists may have irrevocably cleared self-sustaining cyanobacterial ecosystems, thereby creating the ecological opportunity that allowed for the persistent rise of eukaryotic algae to global importance.
hydrothermal carbon release to the ocean and atmosphere from the eastern equatorial pacific during the last glacial termination
lowell douglas stott et al. 2019
http://dx.doi.org/10.1088/1748-9326/aafe28
If undersea carbon reservoirs are upset again, they would emit a huge new source of greenhouse gases, exacerbating climate change. Temperature increases in the ocean are on pace to reach that tipping point by the end of the century. For example, a big carbon reservoir beneath the western Pacific near Taiwan is already within a few degrees Celsius of destabilizing.
Moreover, the phenomenon is a threat unaccounted for in climate model projections. Undersea carbon dioxide reservoirs are relatively recent discoveries and their characteristics and history are only beginning to be understood.
Those findings come from a new research paper produced by an international team of Earth scientists led by USC and published in January in the journal Environmental Research Letters.
"We're using the past as a way to anticipate the future," said Lowell Stott, professor of Earth sciences at the USC Dornsife College of Letters, Arts and Sciences and lead author of the study. "We know there are vast reservoirs of carbon gas at the bottom of the oceans. We know when they were disrupted during the Pleistocene it warmed the planet.
"We have to know if these carbon reservoirs could be destabilized again. It's a wild card for which we need to account," Stott said.
At issue are expanses of carbon dioxide and methane accumulating underwater and scattered across the seafloor. They form as volcanic activity releases heat and gases that can congeal into liquid and solid hydrates, which are compounds stuck together in an icy slurry that encapsulates the reservoirs.
These undersea carbon reservoirs largely stay put unless perturbed, but the new study shows the natural reservoirs are vulnerable in a warming ocean and provides proof the Earth's climate has been affected by rapid release of geologic carbon.
The scientists say it occurred in the distant past when the Earth was much warmer, and it's happened more recently -- about 17,000 years ago at the end of the Pleistocene epoch when glaciers advanced and receded, which is the focus on the new study. Warming was evident due to changes in atmospheric greenhouse gas concentrations, based on ice cores, marine and continental records.
But how did that happen? What forced such dramatic change in the first place? Scientists have been searching for that answer for 40 years, with focus on oceans because they're a giant carbon sink and play a central role in carbon dioxide variations.
They soon realized that processes that regulate carbon to the ocean operated too slowly to account for the surge in atmospheric greenhouse gases that led to warming that ended the ice age. So, scientists around the world began examining the role of Earth's hydrothermal systems and their impact on deep-ocean carbon to see how it affected the atmosphere.
The new study by scientists at USC, the Australian National University and Lund University in Sweden, focused on the Eastern Equatorial Pacific (EEP) hundreds of miles off the coast of Ecuador. The EEP is a primary conduit through which the ocean releases carbon to the atmosphere.
The scientists report evidence of deep-sea hydrothermal systems releasing greenhouse gases to the ocean and atmosphere at the end of the last ice age, just as the oceans were beginning to warm. They measured increased deposition of hydrothermal metals in ancient marine sediments. They correlated glaciation intervals with variations in atmospheric carbon dioxide with differences in marine microorganism ages. They found a four-fold increase in zinc in protozoa (foraminifera) shells, a telltale sign of widespread hydrothermal activity.
Taken together, the new data show that there were major releases of naturally occurring carbon from the EEP, which contributed to dramatic change in Earth's temperature as the ice age was ending, the study says.
Elsewhere around the world, more and more deep-ocean carbon reservoirs are being discovered. They mostly occur near hydrothermal vents, of which scores have been identified so far, especially in the Pacific, Atlantic and Indian oceans. They occur where the Earth's crust spreads or collides, creating ideal conditions for the formation of deep-sea carbon dioxide reservoirs. Only about one-third of the ocean's volcanic regions have been surveyed.
One such reservoir of undersea carbon dioxide, seen in the accompanying video, was discovered about 4,000 feet deep off the coast of Taiwan. Similar discoveries of carbon gas reservoirs have been made off the coast of Okinawa, in the Aegean Sea, in the Gulf of California and off the west coast of Canada.
"The grand challenge is we don't have estimates of the size of these or which ones are particularly vulnerable to destabilization," Stott said. "It's something that needs to be determined."
In many cases, the carbon reservoirs are bottled up by their hydrate caps. But those covers are sensitive to temperature changes. As oceans warm, the caps can melt, a development the paper warns would lead to a double wallop for climate change -- a new source of geologic carbon in addition to the humanmade greenhouse gases.
Oceans absorb nearly all the excess energy from the Earth's atmosphere, and as a result they have been warming rapidly in recent decades. Over the past quarter-century, Earth's oceans have retained 60 percent more heat each year than scientists previously had thought, other studies have shown. Throughout the marine water column, ocean heat has increased for the last 50 years. The federal government's Climate Science Special Report projected a global increase in average sea surface temperatures of up to 5 degrees Fahrenheit by the end of the century, given current emissions rates. Temperature gains of that magnitude throughout the ocean could eventually destabilize the geologic hydrate reservoirs, Stott said.
"The last time it happened, climate change was so great it caused the end of the ice age. Once that geologic process begins, we can't turn it off," Stott said.
Moreover, other similar events have happened in the distant past, helping shape the Earth's environment over and over again. In earlier research, Stott discovered a large, carbon anomaly that occurred 55 million years ago. It disrupted the ocean's chemistry, causing extensive dissolution of marine carbonates and the extinction of many marine organisms. The ocean changes were accompanied by a rapid rise in global temperatures, an event called the Paleocene-Eocene Thermal Maxima (PETM), a period lasting less than 20,000 years during which so much carbon was released to the atmosphere that Earth's temperatures surged to about 8 degrees Celsius hotter than today.
"Until quite recently, we had no idea these events occurred. The PETM event is a good analog for what can happen when undersea carbon escapes through the water column to the atmosphere. And now we know the PETM event was not a unique event, that this has happened more recently," Stott said.
The study comes with some caveats. Much of the ocean floor is unexplored, so scientists don't know the full extent of the carbon dioxide reservoirs. There is no inventory of greenhouse gases from these geologic sources. And ocean warming is not uniform, making it difficult to predict when and where the undersea carbon reservoirs will be affected. It would take much more study to answer those questions.
Nonetheless, the study makes clear the undersea carbon reservoirs are vulnerable to ocean warming.
"Geologic carbon reservoirs such as these are not explicitly included in current marine carbon budgets" used to model the impacts of climate change, the study says. Yet, "even if only a small percentage of the unsampled hydrothermal systems contain separate gas or liquid carbon dioxide phases, it could change the global marine carbon budget substantially."
Said Stott: "Discoveries of accumulations of liquid, hydrate and gaseous carbon dioxide in the ocean has not been accounted for because we didn't know these reservoirs existed until recently, and we didn't know they affected global change in a significant ways.
"This study shows that we've been missing a critical component of the marine carbon budget. It shows these geologic reservoirs can release large amounts of carbon from the oceans. Our paper makes the case that this process has happened before and it could happen again."
abstract Arguably among the most globally impactful climate changes in Earth's past million years are the glacial terminations that punctuated the Pleistocene epoch. With the acquisition and analysis of marine and continental records, including ice cores, it is now clear that the Earth's climate was responding profoundly to changes in greenhouse gases that accompanied those glacial terminations. But the ultimate forcing responsible for the greenhouse gas variability remains elusive. The oceans must play a central role in any hypothesis that attempt to explain the systematic variations in pCO2 because the Ocean is a giant carbon capacitor, regulating carbon entering and leaving the atmosphere. For a long time, geological processes that regulate fluxes of carbon to and from the oceans were thought to operate too slowly to account for any of the systematic variations in atmospheric pCO2 that accompanied glacial cycles during the Pleistocene. Here we investigate the role that Earth's hydrothermal systems had in affecting the flux of carbon to the ocean and ultimately, the atmosphere during the last glacial termination. We document late glacial and deglacial intervals of anomalously old 14C reservoir ages, large benthic-planktic foraminifera 14C age differences, and increased deposition of hydrothermal metals in marine sediments from the Eastern Equatorial Pacific (EEP) that indicate a significant release of hydrothermal fluids entered the ocean at the last glacial termination. The large 14C anomaly was accompanied by a ~4-fold increase in Zn/Ca in both benthic and planktic foraminfera that reflects an increase in dissolved [Zn] throughout the water column. Foraminiferal B/Ca and Li/Ca results from these sites document deglacial declines in [CO32-] throughout the water column; these were accompanied by carbonate dissolution at water depths that today lie well above the calcite lysocline. Taken together, these results are strong evidence for an increased flux of hydrothermally-derived CO2 through the EEP upwelling system at the last glacial termination that would have exchanged with the atmosphere and affected both Δ14C and pCO2. These data do not quantify the amount of carbon released to the atmosphere through the EEP upwelling system but indicate that geologic forcing must be incorporated into models that attempt to simulate the cyclic nature of glacial/interglacial climate variability. Importantly, these results underscore the need to put better constraints on the flux of carbon from geologic reservoirs that affect the global carbon budget.
tectonics
months-long thousand-kilometre-scale wobbling before great subduction earthquakes
jonathan r. bedford et al. 2020
http://dx.doi.org/10.1038/s41586-020-2212-1
The land masses of Japan shifted from east to west to east again in the months before the strongest earthquake in the country's recorded history, a 2011 magnitude-9 earthquake that killed more than 15,500 people, new research shows.
Those movements, what researchers are calling a "wobble," may have the potential to alert seismologists to greater risk of future large subduction-zone earthquakes. These destructive events occur where one of Earth's tectonic plates slides under another one. That underthrusting jams up or binds the earth, until the jam is finally torn or broken and an earthquake results.
The findings were published today (April 30) in the journal Nature.
"What happened in Japan was an enormous but very slow wobble -- something never observed before," said Michael Bevis, a co-author of the paper and professor of earth sciences at The Ohio State University.
"But are all giant earthquakes preceded by wobbles of this kind? We don't know because we don't have enough data. This is one more thing to watch for when assessing seismic risk in subduction zones like those in Japan, Sumatra, the Andes and Alaska."
The wobble would have been imperceptible to people standing on the island, Bevis said, moving the equivalent of just a few millimeters per month over a period of five to seven months. But the movement was obvious in data recorded by more than 1,000 GPS stations distributed throughout Japan, in the months leading up to the March 11 Tohoku-oki earthquake.
The research team, which included scientists from Germany, Chile and the United States, analyzed that data and saw a reversing shift in the land -- about 4 to 8 millimeters east, then to the west, then back to the east. Those movements were markedly different from the steady and cyclical shifts the Earth's land masses continuously make.
"The world is broken up into plates that are always moving in one way or another," Bevis said. "Movement is not unusual. It's this style of movement that's unusual."
Bevis said the wobble could indicate that in the months before the earthquake, the plate under the Philippine Sea began something called a "slow slip event," a relatively gentle and "silent" underthrusting of two adjacent oceanic plates beneath Japan, that eventually triggered a massive westward and downward lurch that drove the Pacific plate and slab under Japan, generating powerful seismic waves that shook the whole country.
That 2011 earthquake caused widespread damage throughout Japan. It permanently shifted large parts of Japan's main island, Honshu, several meters to the east. It launched tsunami waves more than 40 meters high. More than 450,000 people lost their homes. Several nuclear reactors melted down at the Fukushima Daiichi Nuclear Power Plant, sending a steady stream of toxic, radioactive materials into the atmosphere and forcing thousands nearby to flee their homes. It was the worst nuclear disaster since Chernobyl.
Researchers who study earthquakes and plate tectonics try to pinpoint the approximate magnitude of the next large earthquakes and predict where and when they might occur. The "when" is much harder than the "where."
But it won't be possible to use the findings of this study to predict earthquakes in some subduction zones around the world because they don't have the GPS systems needed, said Jonathan Bedford, lead author of this study and a researcher at the GFZ German Research Centre for Geosciences.
In 2011, Japan had one of the largest and most robust GPS monitoring systems in the world. That system provided ample data, and allowed the research team to identify the swing the land mass made in the months leading up to the earthquake.
Other countries, including Chile and Sumatra, which were hit by devastating earthquakes and tsunamis in 2010 and 2004, respectively, had much less-comprehensive systems at the time of those disasters.
The researchers analyzed similar data from the 2010 Chile earthquake, and found evidence of a similar wobble; Bedford said the data was "only just good enough to capture the signal."
"We really need to be monitoring all major subduction zones with high-density GPS networks as soon as possible," he said.
abstract Megathrust earthquakes are responsible for some of the most devastating natural disasters30. To better understand the physical mechanisms of earthquake generation, subduction zones worldwide are continuously monitored with geophysical instrumentation. One key strategy is to install stations that record signals from Global Navigation Satellite Systems31,32 (GNSS), enabling us to track the non-steady surface motion of the subducting and overriding plates before, during and after the largest events4,5,6. Here we use a recently developed trajectory modelling approach7 that is designed to isolate secular tectonic motions from the daily GNSS time series to show that the 2010 Maule, Chile (moment magnitude 8.8) and 2011 Tohoku-oki, Japan (moment magnitude 9.0) earthquakes were preceded by reversals of 4–8 millimetres in surface displacement that lasted several months and spanned thousands of kilometres. Modelling of the surface displacement reversal that occurred before the Tohoku-oki earthquake suggests an initial slow slip followed by a sudden pulldown of the Philippine Sea slab so rapid that it caused a viscoelastic rebound across the whole of Japan. Therefore, to understand better when large earthquakes are imminent, we must consider not only the evolution of plate interface frictional processes but also the dynamic boundary conditions from deeper subduction processes, such as sudden densification of metastable slab.
evidence for a prolonged permian–triassic extinction interval from global marine mercury records
jun shen et al. 2019
http://dx.doi.org/10.1038/s41467-019-09620-0
The extinction 252 million years ago was so dramatic and widespread that scientists call it "the Great Dying." The catastrophe killed off more than 95 percent of life on Earth over the course of hundreds of thousands of years.
Paleontologists with the University of Cincinnati and the China University of Geosciences said they found a spike in mercury in the geologic record at nearly a dozen sites around the world, which provides persuasive evidence that volcanic eruptions were to blame for this global cataclysm.
The study was published this month in the journal Nature Communications.
The eruptions ignited vast deposits of coal, releasing mercury vapor high into the atmosphere. Eventually, it rained down into the marine sediment around the planet, creating an elemental signature of a catastrophe that would herald the age of dinosaurs.
"Volcanic activities, including emissions of volcanic gases and combustion of organic matter, released abundant mercury to the surface of the Earth," said lead author Jun Shen, an associate professor at the China University of Geosciences.
The mass extinction occurred at what scientists call the Permian-Triassic Boundary. The mass extinction killed off much of the terrestrial and marine life before the rise of dinosaurs. Some were prehistoric monsters in their own right, such as the ferocious gorgonopsids that looked like a cross between a sabre-toothed tiger and a Komodo dragon.
The eruptions occurred in a volcanic system called the Siberian Traps in what is now central Russia. Many of the eruptions occurred not in cone-shaped volcanoes but through gaping fissures in the ground. The eruptions were frequent and long-lasting and their fury spanned a period of hundreds of thousands of years.
"Typically, when you have large, explosive volcanic eruptions, a lot of mercury is released into the atmosphere," said Thomas Algeo, a professor of geology in UC's McMicken College of Arts and Sciences.
"Mercury is a relatively new indicator for researchers. It has become a hot topic for investigating volcanic influences on major events in Earth's history," Algeo said.
Researchers use the sharp fossilized teeth of lamprey-like creatures called conodonts to date the rock in which the mercury was deposited. Like most other creatures on the planet, conodonts were decimated by the catastrophe.
The eruptions propelled as much as 3 million cubic kilometers of ash high into the air over this extended period. To put that in perspective, the 1980 eruption of Mount St. Helens in Washington sent just 1 cubic kilometer of ash into the atmosphere, even though ash fell on car windshields as far away as Oklahoma.
In fact, Algeo said, the Siberian Traps eruptions spewed so much material in the air, particularly greenhouse gases, that it warmed the planet by an average of about 10 degrees centigrade.
The warming climate likely would have been one of the biggest culprits in the mass extinction, he said. But acid rain would have spoiled many bodies of water and raised the acidity of the global oceans. And the warmer water would have had more dead zones from a lack of dissolved oxygen.
"We're often left scratching our heads about what exactly was most harmful. Creatures adapted to colder environments would have been out of luck," Algeo said. "So my guess is temperature change would be the No. 1 killer. Effects would exacerbated by acidification and other toxins in the environment."
Stretching over an extended period, eruption after eruption prevented the Earth's food chain from recovering.
"It's not necessarily the intensity but the duration that matters," Algeo said. "The longer this went on, the more pressure was placed on the environment."
Likewise, the Earth was slow to recover from the disaster because the ongoing disturbances continued to wipe out biodiversity, he said.
Earth has witnessed five known mass extinctions over its 4.5 billion years.
Scientists used another elemental signature -- iridium -- to pin down the likely cause of the global mass extinction that wiped out the dinosaurs 65 million years ago. They believe an enormous meteor struck what is now Mexico.
The resulting plume of superheated earth blown into the atmosphere rained down material containing iridium that is found in the geologic record around the world.
Shen said the mercury signature provides convincing evidence that the Siberian Traps eruptions were responsible for the catastrophe. Now researchers are trying to pin down the extent of the eruptions and which environmental effects in particular were most responsible for the mass die-off, particularly for land animals and plants.
Shen said the Permian extinction could shed light on how global warming today might lead to the next mass extinction. If global warming, indeed, was responsible for the Permian die-off, what does warming portend for humans and wildlife today?
"The release of carbon into the atmosphere by human beings is similar to the situation in the Late Permian, where abundant carbon was released by the Siberian eruptions," Shen said.
Algeo said it is cause for concern.
"A majority of biologists believe we're at the cusp of another mass extinction -- the sixth big one. I share that view, too," Algeo said. "What we should learn is this will be serious business that will harm human interests so we should work to minimize the damage."
People living in marginal environments such as arid deserts will suffer first. This will lead to more climate refugees around the world.
"We're likely to see more famine and mass migration in the hardest hit places. It's a global issue and one we should recognize and proactively deal with. It's much easier to address these problems before they reach a crisis."
abstract The latest Permian mass extinction, the most devastating biocrisis of the Phanerozoic, has been widely attributed to eruptions of the Siberian Traps Large Igneous Province, although evidence of a direct link has been scant to date. Here, we measure mercury (Hg), assumed to reflect shifts in volcanic activity, across the Permian-Triassic boundary in ten marine sections across the Northern Hemisphere. Hg concentration peaks close to the Permian-Triassic boundary suggest coupling of biotic extinction and increased volcanic activity. Additionally, Hg isotopic data for a subset of these sections provide evidence for largely atmospheric rather than terrestrial Hg sources, further linking Hg enrichment to increased volcanic activity. Hg peaks in shallow-water sections were nearly synchronous with the end-Permian extinction horizon, while those in deep-water sections occurred tens of thousands of years before the main extinction, possibly supporting a globally diachronous biotic turnover and protracted mass extinction event.
cascading trend of early paleozoic marine radiations paused by late ordovician extinctions
christian m. ø. rasmussen et al. 2019
http://dx.doi.org/10.1073/pnas.1821123116
"One of the problems with the hypothesis of global warming is that it is difficult to predict what happens to ecosystems and biodiversity as the planet warms. By examining animals of the past and species adaptability, we can more accurately respond to the question of what leads to crises in ecosystems, and what happens thereafter. Thus far, it has been a big problem that some of the largest fluctuations in biodiversity through geological time have been exceptionally tough to grasp and accurately date. As such, it has been difficult to compare possible environmental impacts and their effects on biodiversity. Among other things, this is because climate change takes place quite abruptly, in a geological perspective. As previous calculations of biodiversity change in deep time have been based on a time-binning partitioning divided into 10 -- 11 million year intervals, direct comparisons with climate impacts have not been possible. Our new biodiversity curves provide unprecedentedly high temporal resolution, allowing us to take a very large step towards the understanding and coherence of climate-related and environmental impacts on overall biodiversity -- both in relation to species development and extinction event intervals," explains Christian Mac Ørum.
New method ensures better temporal precision
Researchers at the universities of Copenhagen and Helsinki have devised a new method that can provide unprecedented accuracy in the portrayal of biodiversity fluctuations on geological time scales. This has lead to new insight, both in relation to what spurred the largest marine speciation interval in Earth's history, as well as to what caused our planet's second-largest mass extinction event. This method has deployed, among other things, big data and the processing of large quantities of information collected on fossils, climate and historic geological changes. The study covers a prehistoric period characterized by dramatic changes to Earth's climate and environment. Among other things, it documents increasing levels of oxygen and heavy volcanic activity as well as important events that documents the rise in the number of multicellular marine species, such as during the 'Cambrian Explosion'.
"The studies we have been engaged with for over four years have, for the first time, made it possible to compare developments related to biodiversity with climate change, for example. We are now able to see that precisely when ocean temperature fell to its current level, there was also a dramatic increase in biodiversity. This suggests that a cooler climate -- but not too cold -- is very important for conserving biodiversity. Furthermore, we find that the very large extinction event at the end of the Ordovician period (485 -- 443 million years ago), when upwards of 85% of all species disappeared, was not "a brief ice age" -- as previously believed -- but rather a several million years long crisis interval with mass extinctions. It was most likely prompted by increased volcanic activity. It took nearly 40 million years to rectify the mess before biodiversity was on a par with levels prior to this period of volcanic caused death and destruction," emphasizes Christian Mac Ørum.
Extinction events
It is widely accepted that there have been a considerable number of large extinction events throughout Earth's history, with five major extinction events in particular, the "Big Five." These are the three largest:
The largest extinction event occurred 250 million years ago, at the end of the Permian geologic period. 95% of all species are believed to have disappeared as a result of a catastrophe suspected to be due to volcanic activity.
The second largest extinction event occurred 443 million years ago, at the end of the Ordovician geologic period. Until now, it was believed that a sudden global cooling precipitated this event, during which up to 85% of all species became extinct. The new study published in PNAS does away with this assumption and points at volcanism as the main reason.
The most recent major extinction event took place 66 million years ago, when dinosaurs and other forms of life on Earth became extinct. Volcanism and meteor-impact events on Earth are thought to have caused the disappearance of up to 75% of all species. Today, researchers are talking about the planet being in a sixth extinction event prompted by human-induced change, including global warming.
Working methods
Among other things, the researchers have made use of a large database known as 'the Paleobiology Database '. It contains data about fossils collected from across the planet and from different periods of Earth's geological history. Until now, pulling data to provide an overall picture and assessment of the global situation with high temporal resolution has not been possible due to the arduous nature of the process. The new study has overcome this obstacle by first constructing a globally defined schema of 'time intervals' that divided a 120 million-year-long period into 53 'time bins'. They then juxtaposed these bins of time with rock formations in which fossils were found. Then, the researchers analyzed their data using a statistical method typically used by biologists to calculate the prevalence of animal life in a given area. The paleontologists used the method to calculate the diversity of genera per time bin, as well as 'to predict' how many genera ought to occur in subsequent time bin. Not only did this methodology allow for researchers to achieve an unprecedented high temporal accuracy, it also let them account for any lacking fossil remains over geological time.
abstract The first 120 million years of Phanerozoic life witnessed significant changes in biodiversity levels. Attempts to correlate these changes to potential short-term environmental drivers have been hampered by the crude temporal resolution of current biodiversity estimates. We present a biodiversity curve for the Early Paleozoic with high temporal precision. It shows that once equatorial sea-surface temperatures fell to present-day levels during the early Mid Ordovician, marine biodiversity accumulation accelerated dramatically. However, this acceleration ceased as increased volcanism commenced during the mid-Late Ordovician. Since biodiversity levels were not restored for at least ∼35 million years, this finding redefines the nature of the end Ordovician mass extinctions and further reframes the Silurian as a prolonged recovery interval.
The greatest relative changes in marine biodiversity accumulation occurred during the Early Paleozoic. The precision of temporal constraints on these changes is crude, hampering our understanding of their timing, duration, and links to causal mechanisms. We match fossil occurrence data to their lithostratigraphical ranges in the Paleobiology Database and correlate this inferred taxon range to a constructed set of biostratigraphically defined high-resolution time slices. In addition, we apply capture–recapture modeling approaches to calculate a biodiversity curve that also considers taphonomy and sampling biases with four times better resolution of previous estimates. Our method reveals a stepwise biodiversity increase with distinct Cambrian and Ordovician radiation events that are clearly separated by a 50-million-year-long period of slow biodiversity accumulation. The Ordovician Radiation is confined to a 15-million-year phase after which the Late Ordovician extinctions lowered generic richness and further delayed a biodiversity rebound by at least 35 million years. Based on a first-differences approach on potential abiotic drivers controlling richness, we find an overall correlation with oxygen levels, with temperature also exhibiting a coordinated trend once equatorial sea surface temperatures fell to present-day levels during the Middle Ordovician Darriwilian Age. Contrary to the traditional view of the Late Ordovician extinctions, our study suggests a protracted crisis interval linked to intense volcanism during the middle Late Ordovician Katian Age. As richness levels did not return to prior levels during the Silurian—a time of continental amalgamation—we further argue that plate tectonics exerted an overarching control on biodiversity accumulation.
large-scale subduction of continental crust implied by india–asia mass-balance calculation
miquela ingalls, david b. rowley, brian currie, albert s. colman 2016
http://dx.doi.org/10.1038/ngeo2806
evidence of systematic triggering at teleseismic distances following large earthquakes
robert t. o’malley et al. 2018
http://dx.doi.org/10.1038/s41598-018-30019-2
the spatial footprint of injection wells in a global compilation of induced earthquake sequences
thomas h. w. goebel, emily e. brodsky 2018
http://dx.doi.org/10.1126/science.aat5449
elastic impact consequences for high‐frequency earthquake ground motion
victor c. tsai, greg hirth 2020
http://dx.doi.org/10.1029/2019gl086302
Drawing from mathematical models that describe the collisions of rocks during landslides and other debris flows, Tsai and Hirth developed a model that predicts the potential effects of rock collisions in fault zones. The model suggested the collisions could indeed be the principal driver of high-frequency vibrations. And combining the collision model with more traditional frictional slip models offers reasonable explanations for earthquake observations that don’t quite fit the traditional model alone, the researchers say.
For example, the combined model helps explain repeating earthquakes — quakes that happen at the same place in a fault and have nearly identical seismic wave forms. The odd thing about these quakes is that they often have very different magnitudes, yet still produce ground motions that are nearly identical. That’s difficult to explain by slip alone, but makes more sense with the collision model added, the researchers say.
“If you have two earthquakes in the same fault zone, it’s the same rocks that are banging together — or at least rocks of basically the same size,” Tsai said. “So if collisions are producing these high-frequency vibrations, it’s not surprising that you’d get the same ground motions at those frequencies regardless of the amount of slip that occurs.”
The collision model also may help explain why quakes at more mature fault zones — ones that have had lots of quakes over a long period of time — tend to produce less damage compared to quakes of the same magnitude at more immature faults. Over time, repeated quakes tend to grind down the rocks in a fault, making the faults smoother. The collision model predicts that smoother faults with less jagged rocks colliding would produce weaker high-frequency vibrations.
Tsai says that more work needs to be done to fully validate the model, but this initial work suggests the idea is promising. If the model does indeed prove valid, it could be helpful in classifying which faults are likely to produce more or less damaging quakes.
“People have made some observations that particular types of faults seem to generate more or less high-frequency motion than others, but it has not been clear why faults fall into one category or the other,” he said. “What we’re providing is a potential framework for understanding that, and we could potentially generalize this to all faults around the world. Smoother faults with rounded internal structures may generally produce less high-frequency motions, while rougher faults would tend to produce more.”
abstract A fundamental question of earthquake science is what produces damaging high‐frequency ground motion, with the classic Brune‐Haskell model postulating that abrupt fault slip causes it. However, even when amended with heterogeneous rupture, the model fails to explain observations of different sized repeating earthquakes, and has challenges explaining high‐frequency radiation patterns. We propose an additional cause for high‐frequency earthquake spectra from elastic collisions of structures within a rupturing fault zone. The collision spectrum is set by an impact contact time proportional to the size of colliding structures, so that spectra depend on fundamentally different physical parameters compared with slip models. When added to standard models, collisions can reconcile the discrepant observations, since the size, shape and orientation of structures vary between different fault zones but remain constant within a fault segment. High‐frequency earthquake ground motions and damage may therefore be an outgrowth of fault‐zone structure rather than sudden initiation of slip.
variable water input controls evolution of the lesser antilles volcanic arc
cooper, g. f. et al. 2020
doi.org/10.1038/s41586-020-2407-5
“As plates journey from where they are first made at mid-ocean ridges to subduction zones, seawater enters the rocks through cracks, faults and by binding to minerals. Upon reaching a subduction zone, the sinking plate heats up and gets squeezed, resulting in the gradual release of some or all of its water. As water is released it lowers the melting point of the surrounding rocks and generates magma. This magma is buoyant and moves upwards, ultimately leading to eruptions in the overlying volcanic arc. These eruptions are potentially explosive because of the volatiles contained in the melt. The same process can trigger earthquakes and may affect key properties such as their magnitude and whether they trigger tsunamis or not.”
Exactly where and how volatiles are released and how they modify the host rock remains an area of intense research.
Most studies have focused on subduction along the Pacific Ring of Fire. However, this research focused on the Atlantic plate, and more specifically, the Lesser Antilles volcanic arc, located at the eastern edge of the Caribbean Sea.
“This is one of only two zones that currently subduct plates formed by slow spreading. We expect this to be hydrated more pervasively and heterogeneously than the fast spreading Pacific plate, and for expressions of water release to be more pronounced,” said Prof. Saskia Goes, Imperial College London.
The Volatile Recycling in the Lesser Antilles (VoiLA) project brings together a large multidisciplinary team of researchers including geophysicists, geochemists and geodynamicists from Durham University, Imperial College London, University of Southampton, University of Bristol, Liverpool University, Karlsruhe Institute of Technology, the University of Leeds, The Natural History Museum, The Institute de Physique du Globe in Paris, and the University of the West Indies.
“We collected data over two marine scientific cruises on the RRS James Cook, temporary deployments of seismic stations that recorded earthquakes beneath the islands, geological fieldwork, chemical and mineral analyses of rock samples, and numerical modelling,” said Dr Cooper.
To trace the influence of water along the length of the subduction zone, the scientists studied boron compositions and isotopes of melt inclusions (tiny pockets of trapped magma within volcanic crystals). Boron fingerprints revealed that the water-rich mineral serpentine, contained in the sinking plate, is a dominant supplier of water to the central region of the Lesser Antilles arc.
“By studying these micron-scale measurements it is possible to better understand large-scale processes. Our combined geochemical and geophysical data provide the clearest indication to date that the structure and amount of water of the sinking plate are directly connected to the volcanic evolution of the arc and its associated hazards,” said Prof. Colin Macpherson, Durham University
“The wettest parts of the downgoing plate are where there are major cracks (or fracture zones). By making a numerical model of the history of fracture zone subduction below the islands, we found a direct link to the locations of the highest rates of small earthquakes and low shear wave velocities (which indicate fluids) in the subsurface,” said Prof. Saskia Goes.
The history of subduction of water-rich fracture zones can also explain why the central islands of the arc are the largest and why, over geologic history, they have produced the most magma.
abstract Oceanic lithosphere carries volatiles, notably water, into the mantle through subduction at convergent plate boundaries. This subducted water exercises control on the production of magma, earthquakes, formation of continental crust and mineral resources. Identifying different potential fluid sources (sediments, crust and mantle lithosphere) and tracing fluids from their release to the surface has proved challenging35. Atlantic subduction zones are a valuable endmember when studying this deep water cycle because hydration in Atlantic lithosphere, produced by slow spreading, is expected to be highly non-uniform36. Here, as part of a multi-disciplinary project in the Lesser Antilles volcanic arc37, we studied boron trace element and isotopic fingerprints of melt inclusions. These reveal that serpentine—that is, hydrated mantle rather than crust or sediments—is a dominant supplier of subducted water to the central arc. This serpentine is most likely to reside in a set of major fracture zones subducted beneath the central arc over approximately the past ten million years. The current dehydration of these fracture zones coincides with the current locations of the highest rates of earthquakes and prominent low shear velocities, whereas the preceding history of dehydration is consistent with the locations of higher volcanic productivity and thicker arc crust. These combined geochemical and geophysical data indicate that the structure and hydration of the subducted plate are directly connected to the evolution of the arc and its associated seismic and volcanic hazards.
magma
paleolatitude of the hawaiian hot spot since 48 ma: evidence for a mid-cenozoic true polar stillstand followed by late cenozoic true polar wander coincident with northern hemisphere glaciation
daniel woodworth, richard g. gordon 2018
http://dx.doi.org/10.1029/2018GL080787
“The Hawaiian hot spot was fixed, relative to the spin axis, from about 48 million years ago to about 12 million years ago, but it was fixed at a latitude farther north than we find it today,” said Woodworth, a graduate student in Rice’s Department of Earth, Environmental and Planetary Sciences. “By comparing the Hawaiian hot spot to the rest of the Earth, we can see that that shift in location was reflected in the rest of the Earth and is superimposed on the motion of tectonic plates. That tells us that the entire Earth moved, relative to the spin axis, which we interpret to be true polar wander.”
By volume, Earth is mostly mantle, a thick layer of solid rock that flows under intense pressure and heat. The mantle is covered by an interlocking puzzle of rocky tectonic plates that ride atop it, bumping and slipping against one another at seismically active boundaries. Hot spots, like the one beneath Hawaii, are plumes of hot solid rock that rise from deep within the mantle.
Gordon, the W.M. Keck Professor of Earth, Environmental and Planetary Science, said the new findings build on two 2017 studies: one from his lab that showed how to use hot spots as a global frame of reference for tracking the movement of tectonic plates and another from Harvard University that first tied true polar wander to the onset of the ice age.
“We’re taking these hot spots as marked trackers of plumes that come from the deep mantle, and we’re using that as our reference frame,” he said. “We think the whole global network of hotspots was fixed, relative to the Earth’s spin axis, for at least 36 million years before this shift.”
Like any spinning object, Earth is subject to centrifugal force, which tugs on the planet’s fluid interior. At the equator, where this force is strongest, Earth is more than 26 miles larger in diameter than at the poles. Gordon said true polar wander may occur when dense, highly viscous bumps of mantle build up at latitudes away from the equator.
“Imagine you have really, really cold syrup, and you’re putting it on hot pancakes,” Gordon said. “As you pour it, you temporarily have a little pile in the center, where it doesn’t instantly flatten out because of the viscosity of the cold syrup. We think the dense anomalies in the mantle are like that little temporary pile, only the viscosities are much higher in the lower mantle. Like the syrup, it will eventually deform, but it takes a really, really long time to do so.”
If the mantle anomalies are massive enough, they can unbalance the planet, and the equator will gradually shift to bring the excess mass closer to the equator. The planet still spins once every 24 hours and true polar wander does not affect the tilt of the Earth’s spin axis relative to the sun. The redistribution of mass to a new equator does change Earth’s poles, the points on the planet’s surface where the spin axis emerges.
Woodworth said the hot spot data from Hawaii provides some of the best evidence that true polar wander was what caused Earth’s poles to start moving 12 million years ago. Islands chains like the Hawaiians are formed when a tectonic plate moves across a hot spot.
“True polar wander shouldn’t change hot spot tracks because the hot spot track is the record of the motion of the plate relative to the hot spot,” Woodworth said.
Gordon said, “It was only about a 3 degree shift, but it had the effect of taking the mantle under the tropical Pacific and moving it to the south, and at the same time, it was shifting Greenland and parts of Europe and North America to the north. That may have triggered what we call the ice age.”
Earth is still in an ice age that began about 3.2 million years ago. Earth’s poles have been covered with ice throughout the age, and thick ice sheets periodically grow and recede from poles in cycles that have occurred more than 100 times. During these glacial cycles, ice has extended as far south as New York and Yellowstone National Park. Earth today is in an interglacial period in which ice has receded toward the poles.
Gordon said true polar wander is not merely a change in the location of Earth’s magnetic poles. As the planet spins, it’s iron core produces a magnetic field with “north” and “south” poles near the spin axis. The polarity of this field flips several times every million years, and these changes in polarity are recorded in the magnetic signatures of rocks the world over. The paleomagnetic record, which is often used to study the movement of tectonic plates across Earth’s surface, contains many instances of “apparent polar wander,” which tracks the motion of the spin axis and which includes the effects of both plate motion and true polar wander, Gordon said.
He said Earth’s mantle is ever-changing as new material constantly cycles in and out from tectonic plates. The drawing down and recycling of plates via subduction provides a possible explanation for the highly viscous mantle anomalies that probably cause true polar wander.
“In class, I often demonstrate this with lead fishing weights and pliers,” Gordon said. “It’s easy to deform the lead with the pliers, and it’s not brittle. It doesn’t crack or fly apart when it fails. That’s a pretty good analogy for mantle flow because that’s the way silicate rock deforms under intense heat and pressure.”
He and Woodworth are working with colleagues to extend their analysis, both from 12 million years ago to the present as well as further into the past than the 48-million-year start date in the newly published study.
abstract Paleospin axis locations since 48 Ma inferred from the distribution of equatorial sediment accumulation rates on the Pacific plate, together with paleomagnetic poles from magnetic anomaly skewness, indicate that the Hawaiian hot spot was nearly fixed in latitude from 48 to 12 Ma, but ≈3° north of its current latitude. From 48 to 12 Ma in the Pacific hot spot reference frame, which we take to be equivalent to the global hot spot reference frame, the spin axis was located near 87°N, 164°E, recording a stillstand in true polar wander. Global hot spots shifted coherently relative to the spin axis since ≈12 Ma, consistent with an episode of true polar wander, which may continue today. The motion of the spin axis away from the Hawaiian hot spot and toward Greenland since ≈12 Ma coincided with, and may have contributed to, the onset of northern hemisphere glaciation.
Plain Language Summary
The Earth has shifted relative to its spin axis over the past 12 million years (Ma). This shift, which geoscientists call true polar wander, caused the Earth’s mantle beneath the tropical Pacific to move southward while causing Greenland to move northward. The latter motion may have contributed to the onset of the current ice age, which began ≈3 Ma before present. These conclusions follow our analysis of the history of motion of the Pacific tectonic plate relative to the spin axis, which is preserved in sediments and rocks on the Pacific seafloor. We also infer the motion of the Pacific plate relative to the solid Earth from the plate’s history of motion relative to hot spots, such as Hawaii. Hot spots are sites of voluminous volcanism, thought to lie over rising plumes of hot rock from deep in the Earth’s mantle. As the Pacific plate moves over the Hawaiian plume, it creates a line of extinct volcanoes that record the motion of the plate relative to the plume. Combining this information, we find that Hawaii and other global hot spots were nearly fixed in latitude from 48 to 12 Ma before present, which marks a 36‐Ma‐long time interval preceding the shift.
magma mush, not in a chamber
chemical differentiation, cold storage and remobilization of magma in the earth’s crust
m. d. jackson et al. 2018
http://dx.doi.org/10.1038/s41586-018-0746-2
volcanoes are fed by so-called 'mush reservoirs' -- areas of mostly solid crystals with magma in the small spaces between the crystals.
Our understanding of volcanic processes, including those leading to the largest eruptions, has been based on magma being stored in liquid-filled 'magma' chambers -- large, underground caves full of liquid magma. However, these have never been observed.
The new study, by researchers at Imperial College London and the University of Bristol and published today in Nature, suggests the fundamental assumption of a magma chamber needs a re-think.
Lead author Professor Matthew Jackson, from the Department of Earth Sciences and Engineering at Imperial, said: "We now need to look again at how and why eruptions occur from mush reservoirs. We can apply our findings to understanding volcanic eruptions with implications for public safety and also to understand the formation of metal ore deposits associated with volcanic systems."
In order to erupt, volcanoes need a source of magma -- melted, liquid rock -- containing relatively few solid crystals. Traditionally, this magma was thought to be formed and stored in a large underground cave, called a magma chamber.
Recent studies of magma chemistry have challenged this view, leading to the suggestion of the mush reservoir model, where smaller pools of magma sit in the small gaps between solid crystals. However, the mush reservoir model could not explain how magmas containing relatively few crystals arise and are delivered to volcanoes in order for them to erupt at the surface.
Now, with sophisticated modelling of mush reservoirs, the research team has come up with a solution. Within the mush reservoir scenario, the magma is less dense than the crystals, causing it to rise up through the spaces between them.
As it rises, the magma reacts with the crystals, melting them and leading to local areas containing magma with relatively few crystals. It is these short-lived areas of increased magma that can lead to eruptions.
Co-author Professor Stephen Sparks, from the University of Bristol's School of Earth Sciences, said: "A major mystery about volcanoes is that they were thought to be underlain by large chambers of molten rock. Such magma chambers, however, were very difficult to find.
"The new idea developed by geologists at Imperial and Bristol is that molten rock forms within largely crystalline hot rocks, spending most of its time in little pores within the rock rather than in large magma chambers. However, the rock melt is slowly squeezed out to form pools of melt, which can then erupt or form ephemeral magma chambers."
As well as the initiation of eruptions, the new mush reservoir model can help explain other phenomena in volcanic systems, such as how the magma chemical composition evolves and how much older crystals can be erupted within younger magmas.
abstract The formation, storage and chemical differentiation of magma in the Earth’s crust is of fundamental importance in igneous geology and volcanology. Recent data are challenging the high-melt-fraction ‘magma chamber’ paradigm that has underpinned models of crustal magmatism for over a century, suggesting instead that magma is normally stored in low-melt-fraction ‘mush reservoirs’1,2,3,4,5,6,7,8,9. A mush reservoir comprises a porous and permeable framework of closely packed crystals with melt present in the pore space1,10. However, many common features of crustal magmatism have not yet been explained by either the ‘chamber’ or ‘mush reservoir’ concepts1,11. Here we show that reactive melt flow is a critical, but hitherto neglected, process in crustal mush reservoirs, caused by buoyant melt percolating upwards through, and reacting with, the crystals10. Reactive melt flow in mush reservoirs produces the low-crystallinity, chemically differentiated (silicic) magmas that ascend to form shallower intrusions or erupt to the surface11,12,13. These magmas can host much older crystals, stored at low and even sub-solidus temperatures, consistent with crystal chemistry data6,7,8,9. Changes in local bulk composition caused by reactive melt flow, rather than large increases in temperature, produce the rapid increase in melt fraction that remobilizes these cool- or cold-stored crystals. Reactive flow can also produce bimodality in magma compositions sourced from mid- to lower-crustal reservoirs14,15. Trace-element profiles generated by reactive flow are similar to those observed in a well studied reservoir now exposed at the surface16. We propose that magma storage and differentiation primarily occurs by reactive melt flow in long-lived mush reservoirs, rather than by the commonly invoked process of fractional crystallization in magma chambers14.
crustal inheritance and a top-down control on arc magmatism at mount st helens
paul a. bedrosian et al. 2018
http://dx.doi.org/10.1038/s41561-018-0217-2
Previous imaging studies have primarily utilized seismic methods. During natural earthquakes and artificially induced tremors — by setting off explosions — scientists can image some of the properties of subsurface rocks by tracking the sound waves. This method provides clues to the structure, density and temperature of the rocks.
More recently, researchers are using “magnetotelluric,” or MT data, which measures the Earth’s subsurface electrical conductivity. Variations in the geomagnetic and geoelectric fields can reveal much about the subsurface structure and temperature, as well as the presence of fluids such as magma.
“Either method by itself can lead to a level of uncertainty, but when you layer them together as we have done in this project you get a much clearer picture of what lies below,” said Adam Schultz, an Oregon State University geophysicist who is principal investigator on the NSF grant to OSU and co-author on the Nature Geoscience paper.
“The longer you run the measurements, the crisper the images and the deeper you can ‘see’ the subsurface. We were focusing on the upper 12-15 kilometers of the crust, but with a longer experiment we could see 200 to 300 kilometers below the surface.”
Understanding the formation of Mount St. Helens begins with plate tectonics. Similar to the present day, where the Juan de Fuca plate is being subducted beneath North America, in the past crustal blocks with marine sediments were “slammed into the continent, where they accreted,” Schultz said.
“This material is more permeable than surrounding rock and allows the magma to move through it,” he noted. “The big batholith acts kind of like a plug in the crust and diverted magma that normally would have erupted in line with the other major Cascade volcanoes, resulting in St. Helens forming to the west of the Cascadia Arc, and Mt. Adams slightly to the east.”
Mount St. Helens experienced a major eruption in May of 1980 and since has gone through periods of dome-building (2004-08) and dormancy. A study in 2006 by researchers from the University of Canterbury in New Zealand provided some images of the volcano’s subsurface. During the next year, Schultz and the author of the 2006 study will use magnetotelluric technology to gather new and hopefully crisper images to see how much has changed since that study.
Schultz said that the images from the latest study are clear enough that by continuously monitoring the geoelectric and geomagnetic fields, they may be able to detect changes in the movement of magma beneath Mount St. Helens, and perhaps other volcanoes.
“This may give us a new tool to monitor the magma cycle so we don’t have to wait for the dome-building phase to tell us conditions are changing,” Schultz said.
In a subduction zone, the volcanic arc marks the location where magma, generated via flux melting in the mantle wedge, migrates through the crust and erupts. While the location of deep magma broadly defines the arc position, here we argue that crustal structures, identified in geophysical data from the Washington Cascades magmatic arc, are equally important in controlling magma ascent and defining the spatial distribution and compositional variability of erupted material. As imaged by a three-dimensional resistivity model, a broad lower-crustal mush zone containing 3–10% interconnected melt underlies this segment of the arc, interpreted to episodically feed upper-crustal magmatic systems and drive eruptions. Mount St Helens is fed by melt channelled around a mid-Tertiary batholith also imaged in the resistivity model and supported by potential–field data. Regionally, volcanism and seismicity are almost exclusive of the batholith, while at Mount St Helens, along its margin, the ascent of viscous felsic melt is enabled by deep-seated metasedimentary rocks. Both the anomalous forearc location and composition of St Helens magmas are products of this zone of localized extension along the batholith margin. This work is a compelling example of inherited structural control on local stress state and magmatism.
magmatic crystal records in time, space, and process, causatively linked with volcanic unrest
matthew j. pankhurst et al. 2018
http://dx.doi.org/10.1016/j.epsl.2018.04.025
•Olivine crystals are used to retrieve chemical and chronological information.
•A dynamic petrogenetic scenario is proposed to account for disequilibrium patterns.
•Scenario is deterministic and has greater explanatory power than magma mixing.
•Detailed temporal and spatial information at the volcanic plumbing system scale.
•Remarkable agreement with geodetic (real-time remote sensing) data.
How a volcano has behaved throughout its past is a guide to its future behaviour. Detailed knowledge of what preceded eruptions from specific volcanoes, and how this can be recognised in real-time, are pivotal questions of this field. Here, the physical history of the magma that erupted in 2010 from the flank of Eyjafjallajökull volcano, Iceland, is reconstructed in absolute time and space using only chemical records from erupted crystals. The details of this reconstruction include the number of magma bodies, their geometry, their depth, their relative inflation rate and changes to all of the aforementioned through time. Petrology and geodesy (data gathered in real-time) arrive at the same set of conclusions. As such, we report detailed agreement, which demonstrates a causative link between knowledge determined post-eruption via a physical–chemical perspective and knowledge gained syn-eruption from monitoring signals.
the mechanism of tidal triggering of earthquakes at mid-ocean ridges
christopher h. scholz et al. 2019
http://dx.doi.org/10.1038/s41467-019-10605-2
there’s no intrinsic stress that has to be exceeded to cause an earthquake
described the fault as a tilted plane that separates two blocks of earth. During movement, the upper block slides down with respect to the lower one. So, scientists expected that at high tides, when there is more water sitting on top of the fault, it would push the upper block down and cause the earthquakes. But that's not what happens. Instead, the fault slips down during low tide, when forces are actually pulling upwards -- "which is the opposite of what you'd expect," said Scholz.
To get to the bottom the mystery, he, Tan, and Fabien Albino from the University of Bristol studied the Axial Volcano along the Juan de Fuca Ridge in the Pacific Ocean. Because the volcano erupts every ten years or so, scientists have set up dense networks of ocean bottom instruments to monitor it. The team used the data from those instruments to model and explore different ways the low tides could be causing the tremors.
In the end, it came down to a component that no one else had considered before: the volcano's magma chamber, a soft, pressurized pocket below the surface. The team realized that when the tide is low, there is less water sitting on top of the chamber, so it expands. As it puffs up, it strains the rocks around it, forcing the lower block to slide up the fault, and causing earthquakes in the process.
Furthermore, said Scholz, the tidal earthquakes in this region are "so sensitive that we can see details in the response that nobody could ever see before." When the team charted the earthquake rate versus the stress on the fault, they realized that even the tiniest stress could trigger an earthquake. The tidal data helped to calibrate this effect, but the triggering stress could be caused by anything -- such as the seismic waves from another earthquake, or fracking wastewater pumped into the ground.
"People in the hydrofracking business want to know, is there some safe pressure you can pump and make sure you don't produce any earthquakes?" said Scholz. "And the answer that we find is that there isn't any -- it can happen at any level of stress."
Of course, a small stress over a small area isn't going to cause a devastating earthquake, and the exact amount of stress needed varies from place to place. "Our point is there's no intrinsic stress that has to be exceeded to cause an earthquake," says Scholz. "There isn't any rule of thumb."
abstract The strong tidal triggering of mid-ocean ridge earthquakes has remained unexplained because the earthquakes occur preferentially during low tide, when normal faulting earthquakes should be inhibited. Using Axial Volcano on the Juan de Fuca ridge as an example, we show that the axial magma chamber inflates/deflates in response to tidal stresses, producing Coulomb stresses on the faults that are opposite in sign to those produced by the tides. When the magma chamber’s bulk modulus is sufficiently low, the phase of tidal triggering is inverted. We find that the stress dependence of seismicity rate conforms to triggering theory over the entire tidal stress range. There is no triggering stress threshold and stress shadowing is just a continuous function of stress decrease. We find the viscous friction parameter A to be an order of magnitude smaller than laboratory measurements. The high tidal sensitivity at Axial Volcano results from the shallow earthquake depths.
extreme rainfall triggered the 2018 rift eruption at kīlauea volcano
jamie i. farquharson, falk amelung 2020
http://dx.doi.org/10.1038/s41586-020-2172-5
In May 2018 Kīlauea volcano on the island of Hawaii erupted, touching off months of intense activity. Through August, incandescent lava from fissures spewed hundreds of feet in the air, and billowing ash clouds reached as high as six miles into the atmosphere. Huge lava flows inundated land up and down the Pacific island's southeast coast, destroying hundreds of homes.
Volcanoes erupt when molten rock called magma rises to the surface, and many factors, from the shape of the volcano to the composition of the magma, factor into the timing of eruptions. In the case of Kīlauea , a new, NASA-funded study published April 22 in the journal Nature points to another eruption factor: prolonged, sometimes heavy rainfall in the months leading up to the event.
"We knew that changes to water content in Earth's shallow crust can trigger earthquakes and landslides, and now we know that it can also trigger eruptions," said Falk Amelung, professor of geophysics at the University of Miami Rosenstiel School of Marine and Atmospheric Science and co-author of the study. "Under pressure from magma, wet rock breaks easier than dry rock inside the volcano. That, in turn, forges pathways for magma to travel to Earth's surface."
First, for the 2018 Kīlauea eruption researchers ruled out a common cause: increased pressure in the magma chamber, which, when it becomes great enough, is able to break through the surrounding rock. Scientists can infer increased magma pressure by observing the inflation, or rise, of the surrounding rock. "This pressurization causes the ground to inflate by a few tens of centimeters," Amelung explained. "As we did not see any significant inflation in the year prior to the eruption, we started to think about alternative explanations, which led us to investigating precipitation."
Using a combination of ground-based and NASA satellite measurements of rainfall, the researchers modeled the evolution of fluid pressure caused by sustained rainfall that accumulated in the volcano's interior -- a factor that can directly influence the propensity for magma to break through the surrounding rock, ultimately driving volcanic activity. Based on pre-existing laboratory data and numerical simulations, their model results suggest that, in early 2018, fluid pressure had been at its highest in almost half a century, weakening the volcanic edifice, which the authors propose enabled magma to break through confining rock beneath the volcano and lead to the subsequent eruption.
"Interestingly, when we investigate Kīlauea 's historical eruption record, we see that magmatic intrusions and recorded eruptions are almost twice as likely to occur during the wettest parts of the year," said Jamie Farquharson, a postdoctoral researcher at the Rosenstiel School and lead author of the study. He argues that local rainfall patterns may contribute significantly to the timing and frequency of these phenomena at Kīlauea and perhaps at other volcanoes.
While rainfall infiltration has been linked to small steam explosions and volcanic earthquakes, this is the first time that scientists attribute months of above-average rainfall to explain magmatic processes more than a mile below the surface. In the case of the Kīlauea eruption, the first quarter's total rainfall over the volcano that year was about 2.25 meters compared to the 0.9-meter average for the area in that timeframe over the past 20 years. The authors note that if this process occurs as proposed at Kīlauea , then it is likely to occur elsewhere as well.
A climatic link may also be at play, Farquharson said, as ongoing climate change is predicted to bring about changes in rainfall patterns. In particular, most models project increases in extreme precipitation over most of the globe, an effect that may be further amplified in mountainous volcanic regions. "As a result, we expect that rainfall-induced volcanic activity could become more common."
abstract The May 2018 rift intrusion and eruption of Kīlauea Volcano, Hawai‘i, represented one of its most extraordinary eruptive sequences in at least 200 years, yet the trigger mechanism remains elusive38. The event was preceded by several months of anomalously high precipitation. It has been proposed that rainfall can modulate shallow volcanic activity39,40, but it remains unknown whether it can have impacts at the greater depths associated with magma transport. Here we show that immediately before and during the eruption, infiltration of rainfall into Kīlauea Volcano’s subsurface increased pore pressure at depths of 1 to 3 kilometres by 0.1 to 1 kilopascals, to its highest pressure in almost 50 years. We propose that weakening and mechanical failure of the edifice was driven by changes in pore pressure within the rift zone, prompting opportunistic dyke intrusion and ultimately facilitating the eruption. A precipitation-induced eruption trigger is consistent with the lack of precursory summit inflation, showing that this intrusion—unlike others—was not caused by the forceful intrusion of new magma into the rift zone. Moreover, statistical analysis of historic eruption occurrence suggests that rainfall patterns contribute substantially to the timing and frequency of Kīlauea’s eruptions and intrusions. Thus, volcanic activity can be modulated by extreme rainfall triggering edifice rock failure—a factor that should be considered when assessing volcanic hazards. Notably, the increasingly extreme weather patterns associated with ongoing anthropogenic climate change could increase the potential for rainfall-triggered volcanic phenomena worldwide.
tsunami
highly variable recurrence of tsunamis in the 7,400 years before the 2004 indian ocean tsunami
charles m. rubin et al. 2017
dx.doi.org/10.1038/NCOMMS16019
palaeo-tsunami inundation distances deduced from roundness of gravel particles in tsunami deposits
daisuke ishimura, keitaro yamada et al. 2019
dx.doi.org/10.1038/s41598-019-46584-z
tsunami-causing seismic events around subduction zones (where one tectonic plate dips underneath another plate) recur once every 100 to 1,000 years, significantly reducing the number of accurately documented events. It is highly desirable that we gain some understanding by looking at geological deposits instead. However, despite some success in finding the number and age of past events, it is not yet possible to estimate the magnitude of ancient tsunamis, particularly in narrow coastal lowlands like the Sanriku Coast in Japan, struck by the 2011 Tohoku earthquake and tsunami.
Therefore, Assistant Professor Daisuke Ishimura from Tokyo Metropolitan University and Postdoctoral Fellow Keitaro Yamada from Ritsumeikan University carried out studies of gravel samples collected from bore holes and the trench in Koyadori, situated in the middle of the Sanriku coastline. Geological samples were taken corresponding to three tsunami events (AD 1611, 1896 and 2011) whose magnitudes are known, specifically their "inundation distance," or how far they reach inland. They used automated image analysis to study how "round" each gravel particle was in their samples, giving 10 to 100 times more data than existing, manual methods. Comparing distributions with measurements of modern beach and fluvial (river) gravels, they found that they could map the number ratio between beach and fluvial gravel. They discovered that this ratio suddenly changed at a certain distance away from the sea. This point was named the "Tsunami Gravel Inflection Point" (TGIP); it is thought to arise from "run-up" (incoming) waves bringing beach material inland and "return" waves drawing inland material towards the sea. Although the TGIP occurred at different locations for each event, they found that it was always approximately 40% of the inundation distance. They applied this finding to samples corresponding to even older tsunamis, providing estimates for the size of events along the Sanriku Coast going back approximately 4,000 years for the first time.
Although the researchers believe this ratio is specific to the local topography, the same analysis may be applied to characterize other tsunami-prone locations. An accurate estimate of the extent of ancient tsunamis will expand the number of events available for future research to study the mechanisms behind tsunamis, helping to inform effective disaster mitigation and the planning of coastal communities.
abstract Information on palaeo-tsunami magnitude is scientifically and socially essential to mitigate tsunami risk. However, estimating palaeo-tsunami parameters (e.g., inundation distance) from sediments is not simple because tsunami deposits reflect complex transport processes. Here, we show a new approach to estimate tsunami inundation distance based on the mixture ratio of gravels from several sources in tsunami deposits. We measured the roundness of source gravels in modern beach and fluvial deposits in a coastal valley in Japan through image analysis and then calculated the mixture ratio of both sediment types in tsunami deposits. Normalising the mixture ratios by inundation distances revealed an abrupt change in the mixture ratio at a constant percentile, regardless of tsunami magnitude. This relation allowed estimation of the inundation distance of palaeo-tsunamis during the last 4000 years.
surface water
shapes of river networks
robert s. yi et al. 2018
http://dx.doi.org/10.1098/rspa.2018.0081
water input into the mariana subduction zone estimated from ocean-bottom seismic data
chen cai et al. 2018
http://dx.doi.org/10.1038/s41586-018-0655-4
liquids
long-term deep-supercooling of large-volume water and red cell suspensions via surface sealing with immiscible liquids
haishui huang et al. 2018
http://dx.doi.org/10.1038/s41467-018-05636-0
maxima in the thermodynamic response and correlation functions of deeply supercooled water
kyung hwan kim et al. 2017
http://dx.doi.org/10.1126/science.aap8269
unusual proton transfer kinetics in water at the temperature of maximum density
emilia v. silletta et al. 2018
http://dx.doi.org/10.1103/PhysRevLett.121.076001
the base of the lystrosaurus assemblage zone, karoo basin, predates the end-permian marine extinction
robert a. gastaldo et al. 2020
http://dx.doi.org/10.1038/s41467-020-15243-7
The mass extinction at the end of the Permian Peri od 252 million years ago — one of the great turnovers of life on Earth — appears to have played out differently and at different times on land and in the sea, according to newly redated fossils beds from South Africa and Australia.
New ages for fossilized vertebrates that lived just after the demise of the fauna that dominated the late Permian show that the ecosystem changes began hundreds of thousands of years earlier on land than in the sea, eventually resulting in the demise of up to 70% of terrestrial vertebrate species. The later marine extinction, in which nearly 95% of ocean species disappeared, may have occurred over the time span of tens of thousands of years.
Though most scientists believe that a series of volcanic eruptions, occurring in large pulses over a period of a million years in what is now Siberia, were the primary cause of the end-Permian extinction, the lag between the land extinction in the Southern Hemisphere and the marine extinction in the Northern Hemisphere suggests different immediate causes.
“Most people thought that the terrestrial collapse started at the same time as the marine collapse, and that it happened at the same time in the Southern Hemisphere and in the Northern Hemisphere,” said paleobotanist Cindy Looy, University of California, Berkeley, associate professor of integrative biology. “The fact that the big changes were not synchronous in the Northern and Southern hemispheres has a big effect on hypotheses for what caused the extinction. An extinction in the ocean does not, per se, have to have the same cause or mechanism as an extinction that happened on land.”
Members of Looy’s lab have conducted experiments on living plants to determine whether a collapse of Earth’s protective ozone layer may have irradiated and wiped out plant species. Other global changes — a warming climate, a rise in carbon dioxide in the atmosphere and an increase in ocean acidification — also occurred around the end of the Permian period and the beginning of the Triassic and likely contributed.
On land, the end-Permian extinction of vertebrates is best documented in Gondwana, the southern half of the supercontinent known as Pangea that eventually separated into the continents we know today as Antarctica, Africa, South America and Australia. There, in the South African Karoo Basin, populations of large herbivores, or plant eaters, shifted from the Daptocephalus assemblage to the Lystrosaurus assemblage. These groups are now extinct.
In the ocean, the extinction is best documented in the Northern Hemisphere, in particular by Chinese fossils. The end-Permian extinction is perhaps best associated with the demise of trilobites.
To improve on previous dates for the land extinction, an international team of scientists, including Looy, conducted uranium-lead dating of zircon crystals in a well-preserved volcanic ash deposit from the Karoo Basin. Looy, who is also a curator of paleobotany at the campus’s Museum of Paleontology and curator of gymnosperms at the University and Jepson Herbaria, confirmed that sediments from several meters above the dated layer were devoid of Glossopteris pollen, evidence that these seed ferns, which used to dominate late Permian Gondwanan floras, became extinct around that time.
At 252.24 million years old, the zircons — microscopic silicate crystals that form in rising magma inside volcanoes and are spewed into the atmosphere during eruptions — are 300,000 years older than dates obtained for the confirmed Permian-Triassic (P-T) boundary in China. This means that the sediment layer assumed to contain the P-T boundary in South Africa was actually at least 300,000 years too old.
Dates for an ash deposit in Australia, just above the layers that document the initial plant extinction, similarly came in almost 400,000 years older than thought. That work was published in January by Christopher Fielding and colleagues at the University of Nebraska in Lincoln.
“The Karoo Basin is the poster child for the end-Permian vertebrate turnover, but until recently, it was not well-dated,” Looy said. “Our new zircon date shows that the base of the Lystrosaurus zone predates the marine extinction with several hundred thousand years, similar to the pattern in Australia. This means that both the floral and faunal turnover in Gondwana is out of sync with the Northern Hemisphere marine biotic crisis.
“For some years now, we have known that — in contrast to the marine mass extinction — the pulses of disturbance of life on land continued deep into the Triassic Period. But that the start of the terrestrial turnover happened so long before the marine extinction was a surprise.”
In their paper, Looy and an international team of colleagues concluded “that greater consideration should be given to a more gradual, complex, and nuanced transition of terrestrial ecosystems during the Changhsingian (the last part of the Permian) and, possibly, the early Triassic.”
abstract The current model for the end-Permian terrestrial ecosystem crisis holds that systematic loss exhibited by an abrupt turnover from the Daptocephalus to the Lystrosaurus Assemblage Zone (AZ; Karoo Basin, South Africa) is time equivalent with the marine Permian–Triassic boundary (PTB). The marine event began at 251.941 ± 0.037 Ma, with the PTB placed at 251.902 ± 0.024 Ma (2σ). Radio-isotopic dates over this interval in the Karoo Basin were limited to one high resolution ash-fall deposit in the upper Daptocephalus AZ (253.48 ± 0.15 (2σ) Ma) with no similar age constraints for the overlying biozone. Here, we present the first U-Pb CA-ID-TIMS zircon age (252.24 ± 0.11 (2σ) Ma) from a pristine ash-fall deposit in the Karoo Lystrosaurus AZ. This date confirms that the lower exposures of the Lystrosaurus AZ are of latest Permian age and that the purported turnover in the basin preceded the end-Permian marine event by over 300 ka, thus refuting the previously used stratigraphic marker for terrestrial end-Permian extinction.
ephemeral collision complexes mediate chemically termolecular transformations that affect system chemistry
michael p. burke, stephen j. klippenstein 2017
dx.doi.org/10.1038/nchem.2842
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one moment in time
whitney houston
each day i live, i want to be
a day to give the best of me
i’m only one, but not alone
my finest day is yet unknown
i broke my heart for every gain
to taste the sweet, i faced the pain
i rise and fall, yet through it all
this much remains
i want one moment in time
when i’m more than i thought i could be
when all of my dreams are a heartbeat away
and the answers are all up to me
give me one moment in time
when i’m racing with destiny
then in that one moment of time
i will feel, i will feel eternity
i’ve lived to be the very best
i want it all, no time for less
i’ve laid the plans, now lay the chance
here in my hands
for / one moment in time
when we’re more than we thought we could be
when all of our dreams are a heartbeat away
and the answers will all come to be
now is one moment in time
when we’re racing with destiny
now in this one moment in time
we will feel, we will be eternity
you’re a winner for a lifetime if you seize that one moment in time, make it shine
in this one moment in time
when we’re more than we thought we could be
when all of our dreams are a heartbeat away
and the answers all come to be
now is one moment in time
when we’re racing with destiny
here now this one moment through time
we will feel, we will be eternity
dana winner
youtu.be/Tb6AW00DgTI