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Earthquake with magnitude 7.5 in Indonesia—an unusual and steady speed

On the area map on the left, the colored background is the ground displacement induced by the Palu earthquake and the thin black line is the fault, both derived from satellite radar images. The black dot is the city of Palu. The circles are spots that radiated waves during the earthquake; their color indicates time (blue at the beginning, red at the end). The right figure shows the timing and position of these earthquake radiators. Their alignment indicates a steady earthquake speed of about 4.1 km/s Credit: © Han Bao et al., Nature Geoscience
On the area map on the left, the colored background is the ground displacement induced by the Palu earthquake and the thin black line is the fault, both derived from satellite radar images. The black dot is the city of Palu. The circles are spots that radiated waves during the earthquake; their color indicates time (blue at the beginning, red at the end). The right figure shows the timing and position of these earthquake radiators. Their alignment indicates a steady earthquake speed of about 4.1 km/s Credit: © Han Bao et al., Nature Geoscience

An international team of researchers from the French National Research Institute for Sustainable Development (IRD-France), Université Côte d”Azur, University of California Los Angeles and California Institute of Technology has determined the propagation speed of the 7.5 magnitude earthquake which occurred in Indonesia in September 2018: 4.1 km/s along 150 km. The results, which also shed light on the earthquake rupture path, are published on February 4th in Nature Geoscience.

Earthquakes happen when rocks on either side of a tectonic fault shift suddenly in opposite directions. Two main seismic waves that carry out shaking of a breaking fault are S-waves, which shear rocks and propagate at about 3.5 km/s, and P-waves, which compress rocks and propagate faster, at about 5 km/s.

Geophysical observations show that the speed at which an earthquake ruptures along the fault is either slower than S-waves or almost as fast as P-waves. The latter, so-called supershear earthquakes, occur very rarely and can produce very strong shaking. Only a few have been observed, and they happen on faults that are remarkably straight, geological “superhighways” that present little obstacle to speeding earthquakes.

“Forbidden” speed range

In this study, the international team coordinated by Jean-Paul Ampuero, seismologist at IRD and Université Côte d”Azur, analysed the 7.5 magnitude earthquake that rocked the Sulawesi island in Indonesia on September 28th, devastating Palu’s region.

The impact of the event—more than 2,000 deaths—was aggravated by a devastating sequence of secondary effects, involving soil liquefaction, landslides and a tsunami.

Thanks to a high-resolution analysis of seismological data, researchers identified the propagation speed of the earthquake: 4.1 km/s, an unusual speed, between the speed of S- and P-waves. “This is the first time we observed this speed so steadily,” underlines Jean-Paul Ampuero. “This earthquake ran in the ‘forbidden’ speed range, and can be considered as a supershear event, even if it’s not as fast as previous ones.”

By analyzing optical and radar images recorded by satellites especially re-tasked to observe the earthquake aftermath, the researchers determined the path of the fault rupture. They found that the fault was not straight, but had at least two major bends, and left more than five meters of ground offset across the city of Palu. ” This path has major obstacles, which should have reduced the earthquake’s speed, but it stayed at 4.1 km/s along 150 km,” says Jean-Paul Ampuero.

Toward a better anticipation of future earthquakes

The findings challenge current views of earthquakes in ways that could help researchers and public authorities prepare better for future events. “In classical earthquake models, faults live in idealized intact rocks “, says Ampuero, ” but real faults are wrapped in a layer of rocks that have been fractured and softened by previous earthquakes. Steady rupture at speeds that are unexpected on intact rocks can actually happen on damaged rocks, simply because they have slower seismic wave speeds.”

The Palu earthquake may offer the first clear test of such recent models if followed up by studies of the structure of the fault and its zone of damaged rocks. Because the impact of an earthquake depends strongly on its speed, such studies on other faults around the world could anticipate earthquake effects better.

Future work may also determine if the speed of the Palu earthquake enhanced its cascading effects, by promoting coastal and submarine landslides that in turn contributed to the tsunami.

Reference:
Early and persistent supershear rupture of the 2018 magnitude 7.5 Palu earthquake, Nature Geoscience (2019). DOI: 10.1038/s41561-018-0297-z

Note: The above post is reprinted from materials provided by Institut de recherche pour le développement.

Researchers unearth an ice age in the African desert

The drumlins were formed by fast-moving ice floes instead of slow melting ice. Credit: WVU
The drumlins were formed by fast-moving ice floes instead of slow melting ice. Credit: WVU

A field trip to Namibia to study volcanic rocks led to an unexpected discovery by West Virginia University geologists Graham Andrews and Sarah Brown.

While exploring the desert country in southern Africa, they stumbled upon a peculiar land formation—flat desert scattered with hundreds of long, steep hills. They quickly realized the bumpy landscape was shaped by drumlins, a type of hill often found in places once covered in glaciers, an abnormal characteristic for desert landscapes.

“We quickly realized what we were looking at because we both grew up in areas of the world that had been under glaciers, me in Northern Ireland and Sarah in northern Illinois,” said Andrews, an assistant professor of geology. “It’s not like anything we see in West Virginia where we’re used to flat areas and then gorges and steep-sided valleys down into hollows.”

After returning home from the trip, Andrews began researching the origins of the Namibian drumlins, only to learn they had never been studied.

“The last rocks we were shown on the trip are from a time period when southern Africa was covered by ice,” Andrews said. “People obviously knew that part of the world had been covered in ice at one time, but no one had ever mentioned anything about how the drumlins formed or that they were even there at all.”

Andrews teamed up with WVU geology senior Andy McGrady to use morphometrics, or measurements of shapes, to determine if the drumlins showed any patterns that would reflect regular behaviors as the ice carved them.

While normal glaciers have sequential patterns of growing and melting, they do not move much, Andrews explained. However, they determined that the drumlins featured large grooves, which showed that the ice had to be moving at a fast pace to carve the grooves.

These grooves demonstrated the first evidence of an ice stream in southern Africa in the late Paleozoic Age, which occurred about 300 million years ago.

“The ice carved big, long grooves in the rock as it moved,” Andrews said. “It wasn’t just that there was ice there, but there was an ice stream. It was an area where the ice was really moving fast.”

McGrady used freely available information from Google Earth and Google Maps to measure their length, width and height.

“This work is very important because not much has been published on these glacial features in Namibia,” said McGrady, a senior geology student from Hamlin. “It’s interesting to think that this was pioneer work in a sense, that this is one of the first papers to cover the characteristics of these features and gives some insight into how they were formed.”

Their findings also confirm that southern Africa was located over the South Pole during this period.

“These features provide yet another tie between southern Africa and south America to show they were once joined,” Andrews said.

The study, “First description of subglacial megalineations from the late Paleozoic ice age in southern Africa” is published in the Public Library of Science’s PLOS ONE journal.

“This is a great example of a fundamental discovery and new insights into the climatic history of our world that remain to be discovered,” said Tim Carr, chair of the Department of Geology and Geography.

Reference:
Graham D. Andrews et al, First description of subglacial megalineations from the late Paleozoic ice age in southern Africa, PLOS ONE (2019). DOI: 10.1371/journal.pone.0210673

Note: The above post is reprinted from materials provided by West Virginia University.

MERMAIDs reveal secrets from below the ocean floor

Floating seismometers dubbed MERMAIDs -- Mobile Earthquake Recording in Marine Areas by Independent Divers -- reveal that Galapagos volcanoes are fed by a mantle plume reaching 1,900 km deep. By letting their nine MERMAIDs float freely for two years, an international team of researchers created an artificial network of oceanic seismometers that could fill in one of the blank areas on the global geologic map, where otherwise no seismic information is available. Drifting a mile below the surface, MERMAIDs cover a large area. The red circles show where a MERMAID picked up a seismic signal. Credit: Courtesy of the researchers
Floating seismometers dubbed MERMAIDs — Mobile Earthquake Recording in Marine Areas by Independent Divers — reveal that Galapagos volcanoes are fed by a mantle plume reaching 1,900 km deep. By letting their nine MERMAIDs float freely for two years, an international team of researchers created an artificial network of oceanic seismometers that could fill in one of the blank areas on the global geologic map, where otherwise no seismic information is available. Drifting a mile below the surface, MERMAIDs cover a large area. The red circles show where a MERMAID picked up a seismic signal. Credit: Courtesy of the researchers

Seismologists use waves generated by earthquakes to scan the interior of our planet, much like doctors image their patients using medical tomography. Earth imaging has helped us track down the deep origins of volcanic islands such as Hawaii, and identify the source zones of deep earthquakes.

“Imagine a radiologist forced to work with a CAT scanner that is missing two-thirds of its necessary sensors,” said Frederik Simons, a professor of geosciences at Princeton. “Two-thirds is the fraction of the Earth that is covered by oceans and therefore lacking seismic recording stations. Such is the situation faced by seismologists attempting to sharpen their images of the inside of our planet.”

Some 15 years ago, when he was a postdoctoral researcher, Simons partnered with Guust Nolet, now the George J. Magee Professor of Geoscience and Geological Engineering, Emeritus, and they resolved to remediate this situation by building an undersea robot equipped with a hydrophone — an underwater microphone that can pick up the sounds of distant earthquakes whose waves deliver acoustic energy into the oceans through the ocean floor.

This week, Nolet, Simons and an international team of researchers published the first scientific results from the revolutionary seismic floats, dubbed MERMAIDs — Mobile Earthquake Recording in Marine Areas by Independent Divers.

The researchers, from institutions in the United States, France, Ecuador and China, found that the volcanoes on Galápagos are fed by a source 1,200 miles (1,900 km) deep, via a narrow conduit that is bringing hot rock to the surface. Such “mantle plumes” were first proposed in 1971 by one of the fathers of plate tectonics, Princeton geophysicist W. Jason Morgan, but they have resisted attempts at detailed seismic imaging because they are found in the oceans, rarely near any seismic stations.

MERMAIDs drift passively, normally at a depth of 1,500 meters — about a mile below the sea surface — moving 2-3 miles per day. When one detects a possible incoming earthquake, it rises to the surface, usually within 95 minutes, to determine its position with GPS and transmit the seismic data.

By letting their nine robots float freely for two years, the scientists created an artificial network of oceanic seismometers that could fill in one of the blank areas on the global geologic map, where otherwise no seismic information is available.

The unexpectedly high temperature that their model shows in the Galápagos mantle plume “hints at the important role that plumes play in the mechanism that allows the Earth to keep itself warm,” said Nolet.

“Since the 19th century, when Lord Kelvin predicted that Earth should cool to be a dead planet within a hundred million years, geophysicists have struggled with the mystery that the Earth has kept a fairly constant temperature over more than 4.5 billion years,” Nolet explained. “It could have done so only if some of the original heat from its accretion, and that created since by radioactive minerals, could stay locked inside the lower mantle. But most models of the Earth predict that the mantle should be convecting vigorously and releasing this heat much more quickly. These results of the Galápagos experiment point to an alternative explanation: the lower mantle may well resist convection, and instead only bring heat to the surface in the form of mantle plumes such as the ones creating Galápagos and Hawaii.”

To further answer questions on the heat budget of the Earth and the role that mantle plumes play in it, Simons and Nolet have teamed up with seismologists from the Southern University of Science and Technology (SUSTech) in Shenzhen, China, and from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Together, and with vessels provided by the French research fleet, they are in the process of launching some 50 MERMAIDs in the South Pacific to study the mantle plume region under the island of Tahiti.

“Stay tuned! There are many more discoveries to come,” said professor Yongshun (John) Chen, a 1989 Princeton graduate alumnus who is head of the Department of Ocean Science and Engineering at SUSTech, which is leading the next phase of what they and their international team have called EarthScope-Oceans.

Reference:
Guust Nolet, Yann Hello, Suzan van der Lee, Sébastien Bonnieux, Mario C. Ruiz, Nelson A. Pazmino, Anne Deschamps, Marc M. Regnier, Yvonne Font, Yongshun J. Chen, Frederik J. Simons. Imaging the Galápagos mantle plume with an unconventional application of floating seismometers. Scientific Reports, 2019; 9 (1) DOI: 10.1038/s41598-018-36835-w

Note: The above post is reprinted from materials provided by Princeton University.

The 210-million-year-old Smok was crushing bones like a hyena

Coprolites, or fossil droppings, of the dinosaur-like archosaur Smok wawelski contain lots of chewed-up bone fragments. This led researchers at Uppsala University to conclude that this top predator was exploiting bones for salt and marrow, a behavior often linked to mammals but seldom to archosaurs. Credit: Martin Qvarnström
Coprolites, or fossil droppings, of the dinosaur-like archosaur Smok wawelski contain lots of chewed-up bone fragments. This led researchers at Uppsala University to conclude that this top predator was exploiting bones for salt and marrow, a behavior often linked to mammals but seldom to archosaurs. Credit: Martin Qvarnström

Coprolites, or fossil droppings, of the dinosaur-like archosaur Smok wawelski contain lots of chewed-up bone fragments. This led researchers at Uppsala University to conclude that this top predator was exploiting bones for salt and marrow, a behavior often linked to mammals but seldom to archosaurs.

Most predatory dinosaurs used their blade-like teeth to feed on the flesh of their prey, but they are commonly not thought to be much of bone crushers. The major exception is seen in the large tyrannosaurids, such as Tyrannosaurus rex, that roamed North America toward the end of the age of dinosaurs. The tyrannosaurids are thought to have been osteophagous (voluntarily exploiting bone) based on findings of bone-rich coprolites, bite-marked bones, and their robust teeth being commonly worn.

In a study published in Scientific Reports, researchers from Uppsala University were able to link ten large coprolites to Smok wawelski, a top predator of a Late Triassic (210 million year old) assemblage unearthed in Poland. This bipedal, 5-6 meters long animal lived some 140 million years before the tyrannosaurids of North America and had a T. rex-like appearance, although it is not fully clear whether it was a true dinosaur or a dinosaur-like precursor.

Three of the coprolites were scanned using synchrotron microtomography. This method has just recently been applied to coprolites and works somewhat like a CT scanner in a hospital, with the difference that the energy in the x-ray beams is much stronger. This makes it possible to visualize internal structures in fossils in three dimensions.

The coprolites were shown to contain up to 50 percent of bones from prey animals such as large amphibians and juvenile dicynodonts. Several crushed serrated teeth, probably belonging to the coprolite producer itself, were also found in the coprolites. This means that the teeth were repeatedly crushed against the hard food items (and involuntarily ingested) and replaced by new ones.

Further evidence for a bone-crushing behaviour can also be found in the fossils from the same bone beds in Poland. These include worn teeth and bone-rich fossil regurgitates from Smok wawelski, as well as numerous crushed or bite-marked bones.

Several of the anatomical characters related to osteophagy, such as a massive head and robust body, seem to be shared by S. wawelski and the tyrannosaurids, despite them being distantly related and living 140 million years apart. These large predators therefore seem to provide evidence of similar feeding adaptations being independently acquired at the beginning and end of the age of dinosaurs.

Reference:
Martin Qvarnström, Per E. Ahlberg, Grzegorz Niedźwiedzki. Tyrannosaurid-like osteophagy by a Triassic archosaur. Scientific Reports, 2019; 9 (1) DOI: 10.1038/s41598-018-37540-4

Note: The above post is reprinted from materials provided by Uppsala University.

Ancient asteroid impacts played a role in creation of Earth’s future continents

A model for the compositional evolution of the early Earth's crust due to fractional crystallization of impact melt sheets followed by detachment and sinking of their dense primitive portions towards the crust-mantle boundary. Credit: Rais Latypov
A model for the compositional evolution of the early Earth’s crust due to fractional crystallization of impact melt sheets followed by detachment and sinking of their dense primitive portions towards the crust-mantle boundary. Credit: Rais Latypov

The heavy bombardment of terrestrial planets by asteroids from space has contributed to the formation of the early evolved crust on Earth that later gave rise to continents — home to human civilisation.

More than 3.8 billion years ago, in a time period called the Hadean eon, our planet Earth was constantly bombarded by asteroids, which caused the large-scale melting of its surface rocks. Most of these surface rocks were basalts, and the asteroid impacts produced large pools of superheated impact melt of such composition. These basaltic pools were tens of kilometres thick, and thousands of kilometres in diameter.

“If you want to get an idea of what the surface of Earth looked like at that time, you can just look at the surface of the Moon which is covered by a vast amount of large impact craters,” says Professor Rais Latypov from the School of Geosciences of the University of the Witwatersrand in South Africa.

The subsequent fate of these ancient, giant melt sheet remains, however, highly debatable. It has been argued that, on cooling, they may have crystallized back into magmatic bodies of the same, broadly basaltic composition. In this scenario, asteroid impacts are supposed to play no role in the formation of the Earth’s early evolved crust.

An alternative model suggests that these sheets may undergo large-scale chemical change to produce layered magmatic intrusions, such as the Bushveld Complex in South Africa. In this scenario, asteroid impacts may have played an important role in producing various igneous rocks in the early Earth’s crust and therefore they may have contributed to its chemical evolution.

There is no direct way to rigorously test these two competing scenarios because the ancient Hadean impact melts have been later obliterated by plate tectonics. However, by studying the younger impact melt sheet of the Sudbury Igneous Complex (SIC) in Canada, Latypov and his research team have inferred that ancient asteroid impacts were capable of producing various rock types from the earlier Earth’s basaltic crust. Most importantly, these impacts may have made the crust compositionally more evolved, i.e. silica-rich in composition. Their research has been published in a paper in Nature Communications.

The SIC is the largest, best exposed and accessible asteroid impact melt sheet on Earth, which has resulted from a large asteroid impact 1.85 billion years ago. This impact produced a superheated melt sheet of up to 5 km thick. The SIC now shows a remarkable magmatic stratigraphy, with various layers of igneous rocks.

“Our field and geochemical observations — especially the discovery of large discrete bodies of melanorites throughout the entire stratigraphy of the SIC — allowed us to reassess current models for the formation of the SIC and firmly conclude that its conspicuous magmatic stratigraphy is the result of large-scale fractional crystallization,” says Latypov.

“An important implication is that more ancient and primitive Hadean impact melt sheets on the early Earth and other terrestrial planets would also have undergone near-surface, large-volume differentiation to produce compositionally stratified bodies. The detachment of dense primitive layers from these bodies and their sinking into the mantle would leave behind substantial volumes of evolved rocks (buoyant crustal blocks) in the Hadean crust. This would make the crust compositionally layered and increasingly more evolved from its base towards the Earth’s surface.”

“These impacts made the crust compositionally more evolved — in other words, silica-rich in composition,” says Latypov. “Traditionally, researchers believe that such silica-rich evolved rocks — which are essentially building buoyant blocks of our continents — can only be generated deep in the Earth, but we now argue that such blocks can be produced at new-surface conditions within impact melt pools.”

Reference:
Rais Latypov, Sofya Chistyakova, Richard Grieve, Hannu Huhma. Evidence for igneous differentiation in Sudbury Igneous Complex and impact-driven evolution of terrestrial planet proto-crusts. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-08467-9

Note: The above post is reprinted from materials provided by University of the Witwatersrand.

Earth’s largest extinction event likely took plants first

This is a view of Coalcliff in New South Wales, Australia, where researchers discovered evidence that Earth's largest extinction may have extinguished plant life nearly 400,000 years before marine animal species disappeared. Credit: Christopher Fielding
This is a view of Coalcliff in New South Wales, Australia, where researchers discovered evidence that Earth’s largest extinction may have extinguished plant life nearly 400,000 years before marine animal species disappeared. Credit: Christopher Fielding

Little life could endure the Earth-spanning cataclysm known as the Great Dying, but plants may have suffered its wrath long before many animal counterparts, says new research led by the University of Nebraska-Lincoln.

About 252 million years ago, with the planet’s continental crust mashed into the supercontinent called Pangaea, volcanoes in modern-day Siberia began erupting. Spewing carbon and methane into the atmosphere for roughly 2 million years, the eruption helped extinguish about 96 percent of oceanic life and 70 percent of land-based vertebrates — the largest extinction event in Earth’s history.

Yet the new study suggests that a byproduct of the eruption — nickel — may have driven some Australian plant life to extinction nearly 400,000 years before most marine species perished.

“That’s big news,” said lead author Christopher Fielding, professor of Earth and atmospheric sciences. “People have hinted at that, but nobody’s previously pinned it down. Now we have a timeline.”

The researchers reached the conclusion by studying fossilized pollen, the chemical composition and age of rock, and the layering of sediment on the southeastern cliffsides of Australia. There they discovered surprisingly high concentrations of nickel in the Sydney Basin’s mud-rock — surprising because there are no local sources of the element.

Tracy Frank, professor and chair of Earth and atmospheric sciences, said the finding points to the eruption of lava through nickel deposits in Siberia. That volcanism could have converted the nickel into an aerosol that drifted thousands of miles southward before descending on, and poisoning, much of the plant life there. Similar spikes in nickel have been recorded in other parts of the world, she said.

“So it was a combination of circumstances,” Fielding said. “And that’s a recurring theme through all five of the major mass extinctions in Earth’s history.”

If true, the phenomenon may have triggered a series of others: herbivores dying from the lack of plants, carnivores dying from a lack of herbivores, and toxic sediment eventually flushing into seas already reeling from rising carbon dioxide, acidification and temperatures.

‘It Lets Us See What’s Possible’

One of three married couples on the research team, Fielding and Frank also found evidence for another surprise. Much of the previous research into the Great Dying — often conducted at sites now near the equator — has unearthed abrupt coloration changes in sediment deposited during that span.

Shifts from grey to red sediment generally indicate that the volcanism’s ejection of ash and greenhouse gases altered the world’s climate in major ways, the researchers said. Yet that grey-red gradient is much more gradual at the Sydney Basin, Fielding said, suggesting that its distance from the eruption initially helped buffer it against the intense rises in temperature and aridity found elsewhere.

Though the time scale and magnitude of the Great Dying exceeded the planet’s current ecological crises, Frank said the emerging similarities — especially the spikes in greenhouse gases and continuous disappearance of species — make it a lesson worth studying.

“Looking back at these events in Earth’s history is useful because it lets us see what’s possible,” she said. “How has the Earth’s system been perturbed in the past? What happened where? How fast were the changes? It gives us a foundation to work from — a context for what’s happening now.”

The researchers detailed their findings in the journal Nature Communications. Fielding and Frank authored the study with Allen Tevyaw, graduate student in geosciences at Nebraska; Stephen McLoughlin, Vivi Vajda and Chris Mays from the Swedish Museum of Natural History; Arne Winguth and Cornelia Winguth from the University of Texas at Arlington; Robert Nicoll of Geoscience Australia; Malcolm Bocking of Bocking Associates; and James Crowley of Boise State University.

The National Science Foundation and the Swedish Research Council funded the team’s work.

Reference:
Christopher R. Fielding, Tracy D. Frank, Stephen McLoughlin, Vivi Vajda, Chris Mays, Allen P. Tevyaw, Arne Winguth, Cornelia Winguth, Robert S. Nicoll, Malcolm Bocking, James L. Crowley. Age and pattern of the southern high-latitude continental end-Permian extinction constrained by multiproxy analysis. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-018-07934-z

Note: The above post is reprinted from materials provided by University of Nebraska-Lincoln. Original written by Scott Schrage.

How predatory plankton created modern ecosystems after ‘Snowball Earth’

Grand Canyon
Grand Canyon (stock image). Max Planck researchers found 635 million year-old molecules in rock samples from the Grand Canyon, most likely from predatory plankton. The microorganisms probably prepared the soil for today’s ecosystems after the earth thawed again after a phase of complete glaciation. Credit: Bon / Fotolia

Around 635 to 720 million years ago, during Earth’s most severe glacial period, Earth was twice almost completely covered by ice, according to current hypotheses. The question of how life survived these ‘Snowball Earth’ glaciations, lasting up to about 50 million years, has puzzled scientists for many decades. An international team, led by Dutch and German researchers of the Max Planck Society, now found the first detailed glimpse of life after the ‘Snowball’ in the form of newly discovered ancient molecules, buried in old rocks.

“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.

Reference:
Lennart M. van Maldegem, Pierre Sansjofre, Johan W. H. Weijers, Klaus Wolkenstein, Paul K. Strother, Lars Wörmer, Jens Hefter, Benjamin J. Nettersheim, Yosuke Hoshino, Stefan Schouten, Jaap S. Sinninghe Damsté, Nilamoni Nath, Christian Griesinger, Nikolay B. Kuznetsov, Marcel Elie, Marcus Elvert, Erik Tegelaar, Gerd Gleixner, Christian Hallmann. Bisnorgammacerane traces predatory pressure and the persistent rise of algal ecosystems after Snowball Earth. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-08306-x

Note: The above post is reprinted from materials provided by Max-Planck-Gesellschaft.

Earth’s continental nurseries discovered beneath mountains

The central Andes Mountains and surrounding landscape, as seen in this true-color image from NASA’s Terra spacecraft, formed over the past 170 million years as the Nazca Plate lying under the Pacific Ocean has forced its way under the South American Plate. Credit: NASA
The central Andes Mountains and surrounding landscape, as seen in this true-color image from NASA’s Terra spacecraft, formed over the past 170 million years as the Nazca Plate lying under the Pacific Ocean has forced its way under the South American Plate. Credit: NASA

In his free time last summer, Rice University geoscientist Ming Tang made a habit of comparing the niobium content in various rocks in a global minerals database. What he found was worth skipping a few nights out with friends.

In a paper published this month by Nature Communications, Tang, Rice petrologist Cin-Ty Lee and colleagues offered an answer to one of Earth science’s fundamental questions: Where do continents form?

“If our conclusions are correct, every piece of land that we are now sitting on got its start someplace like the Andes or Tibet, with very mountainous surfaces,” said Tang, lead author of the study and a postdoctoral research associate in Rice’s Department of Earth, Environmental and Planetary Sciences (EEPS). “Today, most places are flat because that is the stable stage of the continental crust. But what we found was that when the crust formed, it had to start out with mountain-building processes.”

The connection between niobium, one of Earth’s rarest elements, and continent formation is a story that plays out over billions of years at scales as small as molecules and as large as mountain ranges. The leading players are niobium and tantalum, rare metals so alike that geologists often think of them as twins.

“They have very similar chemical properties and behave almost identically in most geological processes,” Tang said. “If you measure tantalum and niobium, you find that their ratio is nearly constant in Earth’s mantle. That means that when you find more niobium in a rock, you will find more tantalum, and when you find less niobium, you will find less tantalum.”

The mantle is Earth’s thickest layer, spanning about 1,800 miles between the planet’s core and its thin outer crust. Earth scientists believe that little, if anything, moves between the mantle and core, but the mantle and everything above it — seafloor, oceans, continents and atmosphere — are connected, and many of the atoms on Earth’s surface today, including the atoms in humans and other living things, have cycled through the mantle one or more times in Earth’s 4.6 billion years.

The rocks in continents are an exception. Geologists have found some that are up to 4 billion years old, which means they were formed near the surface and stayed on the surface, without being recycled into the mantle. That’s due in part to the nature of continental crust, which is far less dense than the basaltic rocks beneath Earth’s oceans. Lee, professor and EEPS department chair, said it’s no coincidence that Earth is the only rocky planet known to have both continents and life.

“Every day we live on continents, and we take most of our resources from continents,” Lee said. “We have oxygen in the air to breath and just the right temperature to support complex life. These things are so common that we take them for granted, but Earth didn’t start off with these conditions. They developed later in Earth’s history. And the emergence of continents is one of the things that shaped our planet and made it more livable.”

Scientists still lack details about how continents got their start and how they grew to cover 30 percent of Earth’s surface, but one big clue relates to niobium and tantalum, the geochemical twins.

“On average, the rocks in continental crust have about 20 percent less niobium than they should compared to the rock we see everywhere else,” Tang said. “We believe this missing niobium is tied to the mystery of continents. By solving or finding the missing the niobium, we can get important information about how continents form.”

Geologists have known about the imbalance for decades. And it certainly suggests that the geochemical processes that produce continental crust also remove niobium. But where was the missing niobium?

That nagging question prompted Tang to spend his free time perusing records in the Max Planck Institute’s GEOROC database, a comprehensive global collection of published analyses of volcanic rocks.

Based on those searches and months of follow-up tests, Tang, Lee and colleagues offer the first physical evidence that “arclogites” (pronounced ARC-loh-jyts) are responsible for the missing niobium. Arclogites are cumulates, the leftover dross that accumulates near the base of continental arcs. On rare occasions, chunks of these cumulates erupt onto the surface from volcanos.

The Rice group first sent arclogite samples that Lee had collected in Arizona to their collaborator, Kang Chen, a research fellow based at the China University of Geosciences in Wuhan. Chen spent a month getting precise readings of the relative amounts of niobium and tantalum in the samples. The rocks were created when the High Sierras were an active continental arc, like the Andes today.

Chen’s tests confirmed high niobium-tantalum ratios, but to better understand the mechanism by which this signature was developed, Tang and Lee used high precision laser ablation and “inductively coupled plasma mass spectrometry” in Lee’s laboratory at Rice to reveal the mineral rutile was responsible.

“Rutile is the mineral that hosts the niobium,” he said. “It’s a naturally occurring form of titanium oxide, and it is what actually ‘sees’ the difference between niobium and tantalum and captures one more than the other.”

But that happens only under specific conditions. For example, Tang said that at temperatures above 1,000 degrees Celsius, rutile traps normal ratios of tantalum and niobium. It only begins to prefer niobium when temperatures drop below 1,000 degrees Celsius. Tang said the only known place with that set of conditions is deep beneath continental arcs, like the Andes today or the High Sierras about 80 million years ago.

“The reason you need high pressure is that titanium oxide is relatively rare,” he said. “You need very high pressure to force it to crystalize and fall out of the magma.”

In an earlier arclogite study published in Science Advances last May, Tang and Lee discovered a subtle chemical signature that can explain why continental crust is iron-depleted. Lee said that finding and the discovery about rutile and niobium illustrate the central importance of continental arcs in Earth history.

“Continental arcs are like a magic system that links everything together, from climate and oxygen concentrations in the atmosphere to ore deposits,” Lee said. “They’re a sink for carbon dioxide after they die. They can drive greenhouse or icehouse, and they are the building blocks of continents.”

Reference:
Ming Tang, Cin-Ty A. Lee, Kang Chen, Monica Erdman, Gelu Costin, Hehe Jiang. Nb/Ta systematics in arc magma differentiation and the role of arclogites in continent formation. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-018-08198-3

Note: The above post is reprinted from materials provided by Rice University. Original written by Jade Boyd.

Iguana-sized dinosaur cousin discovered in Antarctica

A slab containing fossils of Antarctanax. Credit: Copyright Brandon Peecook, Field Museum
A slab containing fossils of Antarctanax. Credit: Copyright Brandon Peecook, Field Museum

Antarctica wasn’t always a frozen wasteland — 250 million years ago, it was covered in forests and rivers, and the temperature rarely dipped below freezing. It was also home to diverse wildlife, including early relatives of the dinosaurs. Scientists have just discovered the newest member of that family — an iguana-sized reptile whose name means “Antarctic king.”

“This new animal was an archosaur, an early relative of crocodiles and dinosaurs,” says Brandon Peecook, a Field Museum researcher and lead author of a paper in the Journal of Vertebrate Paleontology describing the new species. “On its own, it just looks a little like a lizard, but evolutionarily, it’s one of the first members of that big group. It tells us how dinosaurs and their closest relatives evolved and spread.”

The fossil skeleton is incomplete, but paleontologists still have a good feel for the animal, named Antarctanax shackletoni (the former means “Antarctic king,” the latter is a nod to polar explorer Ernest Shackleton). Based on its similarities to other fossil animals, Peecook and his coauthors (Roger Smith of the University of Witwatersrand and the Iziko South African Museum and Christian Sidor of the Burke Museum and University of Washington) surmise that Antarctanax was a carnivore that hunted bugs, early mammal relatives, and amphibians.

The most interesting thing about Antarctanax, though, is where it lived, and when. “The more we find out about prehistoric Antarctica, the weirder it is,” says Peecook, who is also affiliated with the Burke Museum. “We thought that Antarctic animals would be similar to the ones that were living in southern Africa, since those landmasses were joined back then. But we’re finding that Antarctica’s wildlife is surprisingly unique.”

About two million years before Antarctanax lived — the blink of an eye in geologic time — Earth underwent its biggest-ever mass extinction. Climate change, caused by volcanic eruptions, killed 90% of all animal life. The years immediately after that extinction event were an evolutionary free-for-all — with the slate wiped clean by the mass extinction, new groups of animals vied to fill the gaps. The archosaurs, including dinosaurs, were one of the groups that experienced enormous growth. “Before the mass extinction, archosaurs were only found around the Equator, but after it, they were everywhere,” says Peecook. “And Antarctica had a combination of these brand-new animals and stragglers of animals that were already extinct in most places — what paleontologists call ‘dead clades walking.’ You’ve got tomorrow’s animals and yesterday’s animals, cohabiting in a cool place.”

The fact that scientists have found Antarctanax helps bolster the idea that Antarctica was a place of rapid evolution and diversification after the mass extinction. “The more different kinds of animals we find, the more we learn about the pattern of archosaurs taking over after the mass extinction,” notes Peecook.

“Antarctica is one of those places on Earth, like the bottom of the sea, where we’re still in the very early stages of exploration,” says Peecook. “Antarctanax is our little part of discovering the history of Antarctica.”

Reference:
Brandon R. Peecook, Roger M. H. Smith, Christian A. Sidor. A novel archosauromorph from Antarctica and an updated review of a high-latitude vertebrate assemblage in the wake of the end-Permian mass extinction. Journal of Vertebrate Paleontology, 2019; 1 DOI: 10.1080/02724634.2018.1536664

Note: The above post is reprinted from materials provided by Field Museum.

Long-necked dinosaurs rotated their forefeet to the side

These are well preserved footprints of the find site in Morocco, with clearly visible claw impressions. Credit: The Society of Vertebrate Paleontology
These are well preserved footprints of the find site in Morocco, with clearly visible claw impressions. Credit: The Society of Vertebrate Paleontology

Long-necked dinosaurs (sauropods) could orient their forefeet both forward and sideways. The orientation of their feet depended on the speed and centre of mass of the animals. An international team of researchers investigated numerous dinosaur footprints in Morocco at the foot of the Atlas Mountains using state-of-the-art methods. By comparing them with other sauropods tracks, the scientists determined how the long-necked animals moved forward. The results have now been published in the Journal of Vertebrate Paleontology.

“Long-necked dinosaurs” (sauropods) were among the most successful herbivores of the Mesozoic Era — the age of the dinosaurs. Characteristic for this group were a barrel-shaped body on columnar legs as well as an extremely long neck, which ended in a relatively small head. Long-necked dinosaurs existed from about 210 to 66 million years ago — they thus had been able to assert themselves on earth for a very long period. Also their gigantism, with which they far surpassed other dinosaurs, points at their success.

Sauropods included the largest land animals in Earth history, some over 30 metres long and up to 70 tonnes in weight. “However, it is still unclear how exactly these giants moved,” says Jens Lallensack, paleontologist at the Institute of Geosciences and Meteorology at the University of Bonn in Germany. The limb joints were partly cartilaginous and therefore not fossilised, allowing only limited conclusions about the range of movement.

Detective work with 3D computer analyses

The missing pieces of the puzzle, however, can be reconstructed with the help of fossil footprints of the giants. An international team of researchers from Japan, Morocco and Germany, led by the University of Bonn, has now investigated an unique track site in Morocco at the foot of the Atlas Mountains. The site consists of a surface of 54 x 6 metres which was vertically positioned during mountain formation and shows hundreds of individual footprints, some of which overlap. A part of these footprints could be assigned to a total of nine trackways (sequences of individual footprints). “Working out individual tracks from this jumbled mess of footprints was detective work and only possible through the analysis of high-resolution 3D models on the computer,” says Dr. Oliver Wings of the Zentralmagazin Naturwissenschaftlicher Sammlungen der Martin-Luther-Universität Halle-Wittenberg in Germany.

The researchers were amazed by the results: the trackways are extremely narrow — the right and left footprints are almost in line. Also, the forefoot impressions are not directed forwards, as is typical for sauropod tracks, but point to the side, and sometimes even obliquely backwards. Even more: The animals were able to switch between both orientations as needed. “People are able to turn their palms downwards by crossing the ulna and radius,” says Dr. Michael Buchwitz of the Museum für Naturkunde Magdeburg. However, this complicated movement is limited to mammals and chameleons in today’s terrestrial vertebrates. It was not possible in other animals, including dinosaurs. Sauropods must therefore have found another way of turning the forefoot forwards.

How can the rotation of the forefoot be explained?

How can the rotation of the forefoot in the sauropod tracks be explained? The key probably lies in the mighty cartilage layers, which allowed great flexibility in the joints, especially in the shoulder. But why were the hands rotated outwards at all? “Outwardly facing hands with opposing palms were the original condition in the bipedal ancestors of the sauropods,” explains Shinobu Ishigaki of the Okayama University of Science, Japan. The question should therefore be why most sauropods turned their forefeet forwards — an anatomically difficult movement to implement.

A statistical analysis of sauropod tracks from all over the world could provide important clues: Apparently the animals tended to have outwardly directed forefeet when the foreleg was not used for active locomotion but only for carrying body weight. Thus the forefeet were often rotated further outwards when the animal moved slowly and the centre of mass of the body was far back. Only if the hands were also used for the forward drive, a forefoot directed to the front was advantageous. The analysis furthermore showed that the outer rotation of the forefeet was limited to smaller individuals, whereas in larger animals they were mostly directed forward. The large animals apparently could no longer rotate their forefeet sideways. “This loss of mobility was probably a direct result of their gigantism,” says Lallensack.

Reference:
Jens N. Lallensack, Shinobu Ishigaki, Abdelouahed Lagnaoui, Michael Buchwitz, Oliver Wings. Forelimb Orientation and Locomotion of Sauropod Dinosaurs: Insights from the ?Middle Jurassic Tafaytour Tracksites (Argana Basin, Morocco). Journal of Vertebrate Paleontology, 2019; 1 DOI: 10.1080/02724634.2018.1512501

Note: The above post is reprinted from materials provided by University of Bonn.

Fault lines are no barrier to safe storage of CO2 below ground

Carbon dioxide emissions can be securely stored in underground rocks, with minimal possibility of the gas escaping from fault lines back into the atmosphere, research by the University of Edinburgh has shown. Credit: Johannes Miocic
Carbon dioxide emissions can be securely stored in underground rocks, with minimal possibility of the gas escaping from fault lines back into the atmosphere, research by the University of Edinburgh has shown. Credit: Johannes Miocic

Carbon dioxide emissions can be captured and securely stored in underground rocks, even if geological faults are present, research has confirmed.

There is minimal possibility of the gas escaping from fault lines back into the atmosphere, the study has shown.

The findings are further evidence that an emerging technology known as Carbon Capture and Storage (CCS), in which CO2 gas emissions from industry are collected and transported for underground storage, is reliable.

Such an approach can reduce emissions of CO2 and help to limit the impact of climate change. If widely adopted, CCS could help meet targets set by the 2015 UN Paris Agreement, which seeks to limit climate warming to below 2C compared with pre-industrial levels.

The latest findings, from tests on a naturally occurring CO2 reservoir, may address public concerns over the proposed long-term storage of carbon dioxide in depleted gas and oil fields.

Scientists from the Universities of Edinburgh, Freiburg, Glasgow and Heidelberg studied a natural CO2 repository in Arizona, US, where gas migrates through geological faults to the surface.

Researchers used chemical analysis to calculate the amount of gas that had escaped the underground store over almost half a million years.

They found that a very small amount of carbon dioxide escaped the site each year, well within the safe levels needed for effective storage.

The study, published in Scientific Reports, was supported by the European Union and Natural Environment Research Council.

Dr Stuart Gilfillan, of the University of Edinburgh’s School of GeoSciences, who jointly led the study, said: “This shows that even sites with geological faults are robust, effective stores for CO2. This find significantly increases the number of sites around the world that may be suited to storage of this harmful greenhouse gas.”

Dr Johannes Miocic, of the University of Freiburg, who jointly led the study, said: “The safety of carbon dioxide storage is crucial for successful widespread implementation of much-needed carbon capture and storage technology. Our research shows that even imperfect sites can be secure stores for hundreds of thousands of years.”

Reference:
Johannes M. Miocic, Stuart M. V. Gilfillan, Norbert Frank, Andrea Schroeder-Ritzrau, Neil M. Burnside, R. Stuart Haszeldine. 420,000 year assessment of fault leakage rates shows geological carbon storage is secure. Scientific Reports, 2019; 9 (1) DOI: 10.1038/s41598-018-36974-0

Note: The above post is reprinted from materials provided by University of Edinburgh.

Scientists reconstruct ancient lost plates under Andes mountains

University of Houston researchers John Suppe, left, Jonny Wu and Yi-Wei Chen have reconstructed the ancient plates under the Andes Mountains. Credit: University of Houston
University of Houston researchers John Suppe, left, Jonny Wu and Yi-Wei Chen have reconstructed the ancient plates under the Andes Mountains. Credit: University of Houston

The Andes Mountains are the longest continuous mountain range in the world, stretching about 7,000 kilometers, or 4,300 miles, along the western coast of South America.

The Andean margin, where two tectonic plates meet, has long been considered the textbook example of a steady, continuous subduction event, where one plate slipped under another, eventually forming the mountain range seen today.

In a paper published in the journal Nature, geologists from the University of Houston demonstrate the reconstruction of the subduction of the Nazca Ocean plate, the remnants of which are currently found down to 1,500 kilometers, or about 900 miles, below the Earth’s surface.

Their results show that the formation of the Andean mountain range was more complicated than previous models suggested.

“The Andes Mountain formation has long been a paradigm of plate tectonics,” said Jonny Wu, assistant professor of geology at UH and a co-author of the paper.

When tectonic plates move under the Earth’s crust and enter the mantle, they do not disappear. Rather, they sink toward the core, like leaves sinking to the bottom of a lake. As these plates sink, they retain some of their shape, offering glimpses of what the Earth’s surface looked like millions of years ago.

These plate remnants can be imaged, similar to the way CT scans allow doctors to see inside of a patient, using data gleaned from earthquake waves.

“We have attempted to go back in time with more accuracy than anyone has ever done before. This has resulted in more detail than previously thought possible,” Wu said. “We’ve managed to go back to the age of the dinosaurs.”

Nazca Plate Subduction

The paper describes the deepest and oldest plate remnants reconstructed to date, with plates dating back to the Cretaceous Period.

“We found indications that when the slab reached the transition zone, it created signals on the surface,” said Yi-Wei Chen, a PhD geology student in the UH College of Natural Sciences and Mathematics and first author on the paper. A transition zone is a discontinuous layer in the Earth’s mantle, one which, when a sinking plate hits it, slows the plate’s movement, causing a build-up above it.

In addition to Wu and Chen, John Suppe, Distinguished Professor of Earth and Atmospheric Sciences at UH, is a co-author on the paper.

The researchers also found evidence for the idea that, instead of a steady, continuous subduction, at times the Nazca plate was torn away from the Andean margin, which led to volcanic activity. To confirm this, they modeled volcanic activity along the Andean margin.

“We were able to test this model by looking at the pattern of over 14,000 volcanic records along the Andes,” Wu said.

The work was conducted as part of the UH Center for Tectonics and Tomography, which is directed by Suppe.

“The Center for Tectonics and Tomography brings together experts from different fields in order to relate tomography, which is the imaging of the Earth’s interior from seismology, to the study of tectonics,” Wu said. “For example, the same techniques we use to explore for these lost plates are adapted from petroleum exploration techniques.”

Reference:
Yi-Wei Chen, Jonny Wu & John Suppe. Southward propagation of Nazca subduction along the Andes. Nature, 2019 DOI: 10.1038/s41586-018-0860-1

Note: The above post is reprinted from materials provided by University of Houston.

A reptile platypus from the early Triassic

Complete fossil and line drawing of Eretmorhipis carrolldongi.
Complete fossil and line drawing of Eretmorhipis carrolldongi. Related to the dolphin-like ichthyosaurs, Eretmorhipis evolved in a world devastated by the mass extinction event at the end of the Permian era. Credit: L. Cheng et al, Scientific Reports, Creative Commons 4.0

No animal alive today looks quite like a duckbilled platypus, but about 250 million years ago something very similar swam the shallow seas in what is now China, finding prey by touch with a cartilaginous bill. The newly discovered marine reptile Eretmorhipis carrolldongi from the lower Triassic period is described in the journal Scientific Reports Jan. 24.

Apart from its platypus-like bill, Eretmorhipis was about 70 centimeters long with a long rigid body, small head and tiny eyes, and four flippers for swimming and steering. Bony plates ran down the animal’s back.

Eretmorhipis was previously known only from partial fossils without a head, said Professor Ryosuke Motani, a paleontologist at the University of California, Davis Department of Earth and Planetary Sciences and coauthor on the paper.

“This is a very strange animal,” Motani said. “When I started thinking about the biology I was really puzzled.”

The two new fossils show the animal’s skull had bones that would have supported a bill of cartilage. Like the modern platypus, there is a large hole in the bones in the middle of the bill. In the platypus, the bill is filled with receptors that allow it to hunt by touch in muddy streams.

In the early Triassic, the area was covered by a shallow sea, about a meter deep, over a carbonate platform extending for hundreds of miles. Eretmorhipis fossils were found at what were deeper holes, or lagoons, in the platform. There are no fossils to show what Eretmorhipis ate, but it likely fed on shrimp, worms and other small invertebrates, Motani said.

Its long, bony body means that Eretmorhipis was probably a poor swimmer, Motani said.

“It wouldn’t survive in the modern world, but it didn’t have any rivals at the time,” he said.

Related to the dolphin-like ichthyosaurs, Eretmorhipis evolved in a world devastated by the mass extinction event at the end of the Permian era. The fossil provides more evidence of rapid evolution occurring during the early Triassic, Motani said.

Co-authors on the study are Long Cheng and Chun-bo Yan, Wuhan Centre of China Geological Survey, Wuhan; Da-yong Jiang, Peking University; Andrea Tintori, Università degli Studi di Milano, Italy; and Olivier Rieppel, The Field Museum, Chicago. The work was supported by grants from the China Geological Survey, the National Natural Science Foundation of China and the Ministry of Science and Technology.

Reference:
Long Cheng, Ryosuke Motani, Da-yong Jiang, Chun-bo Yan, Andrea Tintori, Olivier Rieppel. Early Triassic marine reptile representing the oldest record of unusually small eyes in reptiles indicating non-visual prey detection. Scientific Reports, 2019; 9 (1) DOI: 10.1038/s41598-018-37754-6

Note: The above post is reprinted from materials provided by University of California – Davis. Original written by Andy Fell.

Ancient carpet shark discovered with ‘spaceship-shaped’ teeth

One of the tiny fossilized teeth recovered from Galagadon, so named for the shape of its teeth, which resemble the spaceships in the video game Galaga. Credit: Copyright Terry Gates
One of the tiny fossilized teeth recovered from Galagadon, so named for the shape of its teeth, which resemble the spaceships in the video game Galaga. Credit: Copyright Terry Gates

The world of the dinosaurs just got a bit more bizarre with a newly discovered species of freshwater shark whose tiny teeth resemble the alien ships from the popular 1980s video game Galaga.

Unlike its gargantuan cousin the megalodon, Galagadon nordquistae was a small shark (approximately 12 to 18 inches long), related to modern-day carpet sharks such as the “whiskered” wobbegong. Galagadon once swam in the Cretaceous rivers of what is now South Dakota, and its remains were uncovered beside “Sue,” the world’s most famous T. rex fossil.

“The more we discover about the Cretaceous period just before the non-bird dinosaurs went extinct, the more fantastic that world becomes,” says Terry Gates, lecturer at North Carolina State University and research affiliate with the North Carolina Museum of Natural Sciences. Gates is lead author of a paper describing the new species along with colleagues Eric Gorscak and Peter J. Makovicky of the Field Museum of Natural History.

“It may seem odd today, but about 67 million years ago, what is now South Dakota was covered in forests, swamps and winding rivers,” Gates says. “Galagadon was not swooping in to prey on T. rex, Triceratops, or any other dinosaurs that happened into its streams. This shark had teeth that were good for catching small fish or crushing snails and crawdads.”

The tiny teeth — each one measuring less than a millimeter across — were discovered in the sediment left behind when paleontologists at the Field Museum uncovered the bones of “Sue,” currently the most complete T. rex specimen ever described. Gates sifted through the almost two tons of dirt with the help of volunteer Karen Nordquist, whom the species name, nordquistae, honors. Together, the pair recovered over two dozen teeth belonging to the new shark species.

“It amazes me that we can find microscopic shark teeth sitting right beside the bones of the largest predators of all time,” Gates says. “These teeth are the size of a sand grain. Without a microscope you’d just throw them away.”

Despite its diminutive size, Gates sees the discovery of Galagadon as an important addition to the fossil record. “Every species in an ecosystem plays a supporting role, keeping the whole network together,” he says. “There is no way for us to understand what changed in the ecosystem during the mass extinction at the end of the Cretaceous without knowing all the wonderful species that existed before.”

Gates credits the idea for Galagadon’s name to middle school teacher Nate Bourne, who worked alongside Gates in paleontologist Lindsay Zanno’s lab at the N.C. Museum of Natural Sciences.

Reference:
Terry A. Gates, Eric Gorscak, Peter J. Makovicky. New sharks and other chondrichthyans from the latest Maastrichtian (Late Cretaceous) of North America. Journal of Paleontology, 2019; 1 DOI: 10.1017/jpa.2018.92

Note: The above post is reprinted from materials provided by North Carolina State University.

Crocodiles have complex past

Representative Image

A new study throws into question the notion that today’s crocodiles and alligators have a simple evolutionary past.

Previous research has pointed to crocodiles and alligators starting with a land-based ancestor some 200 million years ago and then moving to fresh water, becoming the semi-aquatic ambush predators they are today.

But a new analysis, published online today in the journal Scientific Reports, offers a different story. Modern crocodiles and alligators came from a variety of surroundings beginning in the early Jurassic Period, and various species occupied a host of ecosystems over time, including land, estuarine, freshwater and marine.

As University of Iowa researcher and study co-author Christopher Brochu says, “Crocodiles are not living fossils. Transitions between land, sea, and freshwater were more frequent than we thought, and the transitions were not always land-to-freshwater or freshwater-to-marine.”

Brochu and colleagues from Stony Brook University pieced together crocodile and alligator ancestry by analyzing a large family tree showing the evolutionary history of living and extinct crocodylomorphs (modern crocodiles and alligators and their extinct relatives). The team was then able to predict the ancestral habitat for several divergence points on the evolutionary tree.

This suggests a complex evolutionary history not only of habitat, but of form. Those living at sea had paddles instead of limbs, and those on land often had hoof-like claws and long legs. These did not all evolve from ancestors that looked like modern crocodiles, as has long been assumed.

Reference:
Eric W. Wilberg, Alan H. Turner, Christopher A. Brochu. Evolutionary structure and timing of major habitat shifts in Crocodylomorpha. Scientific Reports, 2019; 9 (1) DOI: 10.1038/s41598-018-36795-1

Note: The above post is reprinted from materials provided by University of Iowa.

Fossilized slime of 100-million-year-old hagfish shakes up vertebrate family tree

Tethymyxine tapirostrum, is a 100-million-year-old, 12-inch long fish embedded in a slab of Cretaceous period limestone from Lebanon, believed to be the first detailed fossil of a hagfish.
Tethymyxine tapirostrum, is a 100-million-year-old, 12-inch long fish embedded in a slab of Cretaceous period limestone from Lebanon, believed to be the first detailed fossil of a hagfish. Credit: Tetsuto Miyashita, University of Chicago

Paleontologists at the University of Chicago have discovered the first detailed fossil of a hagfish, the slimy, eel-like carrion feeders of the ocean. The 100-million-year-old fossil helps answer questions about when these ancient, jawless fish branched off the evolutionary tree from the lineage that gave rise to modern-day jawed vertebrates, including bony fish and humans.

The fossil, named Tethymyxine tapirostrum,is a 12-inch long fish embedded in a slab of Cretaceous period limestone from Lebanon. It fills a 100-million-year gap in the fossil record and shows that hagfish are more closely related to the blood-sucking lamprey than to other fishes. This means that both hagfish and lampreys evolved their eel-like body shape and strange feeding systems after they branched off from the rest of the vertebrate line of ancestry about 500 million years ago.

“This is a major reorganization of the family tree of all fish and their descendants. This allows us to put an evolutionary date on unique traits that set hagfish apart from all other animals,” said Tetsuto Miyashita, PhD, a Chicago Fellow in the Department of Organismal Biology and Anatomy at UChicago who led the research. The findings are published this week in the Proceedings of the National Academy of Sciences.

The slimy dead giveaway

Modern-day hagfish are known for their bizarre, nightmarish appearance and unique defense mechanism. They don’t have eyes, or jaws or teeth to bite with, but instead use a spiky tongue-like apparatus to rasp flesh off dead fish and whales at the bottom of the ocean. When harassed, they can instantly turn the water around them into a cloud of slime, clogging the gills of would-be predators.

This ability to produce slime is what gave away the Tethymyxine fossil. Miyashita used an imaging technology called synchrotron scanning at Stanford University to identify chemical traces of soft tissue that were left behind in the limestone when the hagfish fossilized. These soft tissues are rarely preserved, which is why there are so few examples of ancient hagfish relatives to study.

The scanning picked up a signal for keratin, the same material that makes up fingernails in humans. Keratin, as it turns out, is a crucial part of what makes the hagfish slime defense so effective. Hagfish have a series of glands along their bodies that produce tiny packets of tightly-coiled keratin fibers, lubricated by mucus-y goo. When these packets hit seawater, the fibers explode and trap the water within, turning everything into shark-choking slop. The fibers are so strong that when dried out they resemble silk threads; they’re even being studied as possible biosynthetic fibers to make clothes and other materials.

Miyashita and his colleagues found more than a hundred concentrations of keratin along the body of the fossil, meaning that the ancient hagfish probably evolved its slime defense when the seas included fearsome predators such as plesiosaurs and ichthyosaurs that we no longer see today.

“We now have a fossil that can push back the origin of the hagfish-like body plan by hundreds of millions of years,” Miyashita said. “Now, the next question is how this changes our view of the relationships between all these early fish lineages.”

Shaking up the vertebrate family tree

Features of the new fossil help place hagfish and their relatives on the vertebrate family tree. In the past, scientists have disagreed about where they belonged, depending on how they tackled the question. Those who rely on fossil evidence alone tend to conclude that hagfish are so primitive that they are not even vertebrates. This implies that all fishes and their vertebrate descendants had a common ancestor that — more or less — looked like a hagfish.

But those who work with genetic data argue that hagfish and lampreys are more closely related to each other. This suggests that modern hagfish and lampreys are the odd ones out in the family tree of vertebrates. In that case, the primitive appearance of hagfish and lampreys is deceptive, and the common ancestor of all vertebrates was probably something more conventionally fish-like.

Miyashita’s work reconciles these two approaches, using physical evidence of the animal’s anatomy from the fossil to come to the same conclusion as the geneticists: that the hagfish and lampreys should be grouped separately from the rest of fishes.

“In a sense, this resets the agenda of how we understand these animals,” said Michael Coates, PhD, professor of organismal biology and anatomy at UChicago and a co-author of the new study. “Now we have this important corroboration that they are a group apart. Although they’re still part of vertebrate biodiversity, we now have to look at hagfish and lampreys more carefully, and recognize their apparent primitiveness as a specialized condition.

Paleontologists have increasingly used sophisticated imaging techniques in the past few years, but Miyashita’s research is one of a handful so far to use synchrotron scanning to identify chemical elements in a fossil. While it was crucial to detect anatomical structures in the hagfish fossil, he believes it can also be a useful tool to help scientists detect paint or glue used to embellish a fossil or even outright forge a specimen. Any attempt to spice up a fossil specimen leaves chemical fingerprints that light up like holiday decorations in a synchrotron scan.

“I’m impressed with what Tetsuto has marshaled here,” Coates said. “He’s maxed out all the different techniques and approaches that can be applied to this fossil to extract information from it, to understand it and to check it thoroughly.”

The study, “A Hagfish from the Cretaceous Tethys Sea and a Reconciliation of the Morphological-Molecular Conflict in Early Vertebrate Phylogeny,” was supported by the National Science Foundation and the National Science and Engineering Research Council (Canada). Additional authors include Robert Farrar and Peter Larson from the Black Hills Institute of Geological Research; Phillip Manning and Roy Wogelius from the University of Manchester; Nicholas Edwards and Uwe Bergmann from the SLAC National Accelerator Laboratory; Jennifer Anné from the Children’s Museum of Indianapolis; and Richard Palmer and Philip Currie from the University of Alberta.

Note: The above post is reprinted from materials provided by University of Chicago Medical Center. Original written by Matt Wood.

Large volcanic eruption in Scotland may have contributed to prehistoric global warming

This is a false color electron-microscope image of a resorbed apatite crystal (green) in pitchstone glass (blue). The composition of the pitchstone glass and the characteristic mineral textures are identical in the studied pitchstone sites of the Sgùrr of Eigg and Òigh-sgeir, although over 30km apart, indicating a common origin, and thus a large and geographically widespread volcanic eruption. Credit: Valentin Troll
This is a false color electron-microscope image of a resorbed apatite crystal (green) in pitchstone glass (blue). The composition of the pitchstone glass and the characteristic mineral textures are identical in the studied pitchstone sites of the Sgùrr of Eigg and Òigh-sgeir, although over 30km apart, indicating a common origin, and thus a large and geographically widespread volcanic eruption. Credit: Valentin Troll

Around 56 million years ago, global temperatures spiked. Researchers at Uppsala University and in the UK now show that a major explosive eruption from the Red Hills on the Isle of Skye may have been a contributing factor to the massive climate disturbance. Their findings have been published in the journal Scientific Reports.

Large explosive volcanic eruptions can have lasting effects on climate and have been held responsible for severe climate effects in Earth’s history. One such event occurred around 56 million years ago when global temperatures increased by 5-8 °C. This event has been named the Paleocene-Eocene Thermal Maximum (PETM). The warm period was associated with volcanic activity in the North Atlantic region, especially in Greenland, the British Isles and the present day North Sea region. However, until now, no large-scale explosive eruptions had been confirmed in current-day Scotland.

A team of researchers at Uppsala University, Sweden, the Universities of Durham and St Andrews in the UK, and the Scottish Environmental Research Centre in Glasgow, now seem to have found a missing piece of the puzzle. By studying volcanic rocks called pitchstones from islands more than 30 kilometres apart in the Inner Hebrides off the west coast of Scotland, the researchers have found plausible evidence of a major eruption from what is today the Isle of Skye.

The researchers used several different methods to compare the pitchstones recovered from the two sites (Sgùrr of Eigg and Òigh-sgeir) including isotope geochemistry. Samples from the two pitchstone outcrops display identical textures and compositions in all analyses, confirming that the two outcrops represent deposits of a single, massive and explosive volcanic eruption. The researcher’s geochemical data identify the Red Hills on Skye, around 40 kilometres to the North, as the most likely vent area for this large eruption. Using this vent location, a reconstruction estimates the eruption to have been similar in magnitude to the infamous Krakatoa eruption of 1883, one of the deadliest and most destructive volcanic events in recorded history.

Earth scientists have long thought that the Scottish sector of the North Atlantic Volcanic province did not see any large explosive eruptions at the time of the PETM. This notion is now contradicted by the findings of the current study and the researchers conclude that large explosive volcanic events in the Scottish sector of the North Atlantic Volcanic Province were likely a major contributing factor to the climate disturbance of the PETM.

Around 56 million years ago, global temperatures spiked. Researchers at Uppsala University and in the UK now show that a major explosive eruption from the Red Hills on the Isle of Skye may have been a contributing factor to the massive climate disturbance. Their findings have been published in the journal Scientific Reports.

Large explosive volcanic eruptions can have lasting effects on climate and have been held responsible for severe climate effects in Earth’s history. One such event occurred around 56 million years ago when global temperatures increased by 5-8 °C. This event has been named the Paleocene-Eocene Thermal Maximum (PETM). The warm period was associated with volcanic activity in the North Atlantic region, especially in Greenland, the British Isles and the present day North Sea region. However, until now, no large-scale explosive eruptions had been confirmed in current-day Scotland.

A team of researchers at Uppsala University, Sweden, the Universities of Durham and St Andrews in the UK, and the Scottish Environmental Research Centre in Glasgow, now seem to have found a missing piece of the puzzle. By studying volcanic rocks called pitchstones from islands more than 30 kilometres apart in the Inner Hebrides off the west coast of Scotland, the researchers have found plausible evidence of a major eruption from what is today the Isle of Skye.

The researchers used several different methods to compare the pitchstones recovered from the two sites (Sgùrr of Eigg and Òigh-sgeir) including isotope geochemistry. Samples from the two pitchstone outcrops display identical textures and compositions in all analyses, confirming that the two outcrops represent deposits of a single, massive and explosive volcanic eruption. The researcher’s geochemical data identify the Red Hills on Skye, around 40 kilometres to the North, as the most likely vent area for this large eruption. Using this vent location, a reconstruction estimates the eruption to have been similar in magnitude to the infamous Krakatoa eruption of 1883, one of the deadliest and most destructive volcanic events in recorded history.

Earth scientists have long thought that the Scottish sector of the North Atlantic Volcanic province did not see any large explosive eruptions at the time of the PETM. This notion is now contradicted by the findings of the current study and the researchers conclude that large explosive volcanic events in the Scottish sector of the North Atlantic Volcanic Province were likely a major contributing factor to the climate disturbance of the PETM.

Reference:
Valentin R. Troll, C. Henry Emeleus, Graeme R. Nicoll, Tobias Mattsson, Robert M. Ellam, Colin H. Donaldson, Chris Harris. A large explosive silicic eruption in the British Palaeogene Igneous Province. Scientific Reports, 2019; 9 (1) DOI: 10.1038/s41598-018-35855-w

Note: The above post is reprinted from materials provided by Uppsala University.

International Chronostratigraphic Chart “Version 2018/08”

International Chronostratigraphic Chart “Version 2018/08”
International Chronostratigraphic Chart “Version 2018/08”

Click here (PDF or JPG) to download the latest version (v2018/08) of the International Chronostratigraphic Chart.

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New study quantifies deep reaction behind ‘superdeep’ diamonds

Diamond
The Cullinan Diamond, the largest gem-quality diamond found, was discovered in South Africa in 1905. Superdeep diamonds have been uncovered at the same mine. Credit: Public Domain

Whether they are found in an engagement ring or an antique necklace, diamonds usually generate quick reactions from their recipients. Now, new research shows deep inside the Earth, fast reactions between subducted tectonic plates and the mantle at specific depths may be responsible for generating the most valuable diamonds.

The diamonds mined most often around the world are formed in the Earth’s mantle at depths of around 150-250 kilometers (93-155 miles). They are created by extreme pressure and temperature of at least 1050 degrees Celsius (1922 degrees Fahrenheit). Only a small amount of these diamonds make it to mineable regions since most are destroyed in the process of reaching the Earth’s crust via deep source volcanic eruptions.

But a tiny portion of mined diamonds, called sub-lithospheric or superdeep diamonds, are formed at much deeper depths than others, mostly in two rich zones at depths of 250-450 kilometers (155-279 miles) and 600-800 kilometers (372-497 miles). These diamonds stand out from others due to their compositions, which occasionally include materials from the deep Earth like majorite garnet, ferropericlase and bridgmanite.

“Although only composing 1 percent of the total mined diamonds, it seems lots of large and high-purity diamonds are superdeep diamonds, so they have good value as gems,” said Feng Zhu the lead author of the new study in Geophysical Research Letters, a journal of the American Geophysical Union, who was a post-doctoral geology researcher at the University of Michigan when he performed the research.

No previous theory has completely explained the reason why very few diamonds have been found near the surface from the area at depths of 450-600 kilometers (372-497 miles) – the region between the zones where most superdeep diamonds are formed.

The new study seeks to explain this phenomenon. Zhu, now a post-doctoral researcher at the University of Hawai’i, and his colleagues believe the two superdeep areas where diamonds are formed are rich in the gems due to high production rates. The new study explains what drives the diamond-producing reaction in some areas and what slows it down in other areas.

Diamond formation

According to the authors, diamonds can form anywhere in the mantle, which extends from about 35 to 2,890 kilometers (21-1,800 miles) below the Earth’s surface. However, humans rarely see most of the diamonds formed. Very few diamonds survive the volcanic trip to the Earth’s crust where we can sample them.

That means the chances of finding diamonds from deep regions in the mantle, which produce relatively few of the gems, is extremely small. Only 1 percent of mined diamonds come from superdeep regions.

“In our hypothesis, the production of diamonds at any depth in the mantle is possible, it’s just the production rate is different, so they have a different chance to be sampled in the crust,” Zhu said.

Creating diamonds

In order to mimic the extreme pressures experienced deep inside planets, the study’s authors used diamond anvil cells and a 1,000-ton multi-anvil apparatus at the University of Michigan. Both these devices allow researchers to compress sub-millimeter-sized material in extreme pressures. They compressed magnesium carbonate powder with iron foil in extreme heats and managed to create minuscule diamond grains visible through scanning electron microscopes.

They found that when conditions are right, diamond grains can form as quickly as every couple of minutes, and never took longer than a few hours to form, although the growth of gem diamonds may take much longer time in an actual melting fluid environment.

In the shallower region rich in superdeep diamond formation, 250-450 kilometers (155-279 miles) down, a subducting tectonic plate pushes under the Earth’s mantle. This supplies plenty of carbonate, which creates “factories on a conveyor belt” for diamonds when combined with the iron from the mantle, the authors said.

High temperatures promote reactions which form diamonds, but pressure does the opposite. At depths roughly 475 kilometers (295 miles) below the surface, the pressure increases, and the reactions slow down drastically, the authors said. That’s why few diamonds are found near the Earth surface coming from between 450-600 kilometers (372-497 miles).

“When your pressure reaches the diamond stable region, it will form. But when you increase pressure it will form at lower rates. You have a trade off there,” Zhu said.

One exception to this rule is in the deeper region of 600-800 kilometers (372-497 miles) beneath the surface. In this region, accumulation of carbonate due to the stagnation of tectonic slabs pushing downwards makes up for the overdose in pressure. So while the reactions slow down, higher temperatures and an abundance of carbonate makes for a diamond-rich region.

Zhu said the new study adds to scientists’ understanding of the Earth’s mantle, about which relatively little is known for sure.

“Superdeep diamond inclusions bring us the only mineral samples from the Earth’s deep mantle,” he said. “Seeing is believing, and these inclusions provide a solid ground for the studies on the inaccessible mantle.”

Reference:
Feng Zhu et al. Kinetic control on the depth distribution of superdeep diamonds, Geophysical Research Letters (2018). DOI: 10.1029/2018GL080740

Note: The above post is reprinted from materials provided by American Geophysical Union.This story is republished courtesy of AGU Blogs (http://blogs.agu.org), a community of Earth and space science blogs, hosted by the American Geophysical Union

Scientists find increase in asteroid impacts on ancient Earth by studying the Moon

Image depicts the change in impact rate modeled in this paper. Some of the craters used in the study on both the moon and Earth are highlighted in the background. Credit: Data from NASA GSFC / LRO / Arizona State University; Artwork by Rebecca Ghent
Image depicts the change in impact rate modeled in this paper. Some of the craters used in the study on both the moon and Earth are highlighted in the background. Credit: Data from NASA GSFC / LRO / Arizona State University; Artwork by Rebecca Ghent

An international team of scientists is challenging our understanding of a part of Earth’s history by looking at the Moon, the most complete and accessible chronicle of the asteroid collisions that carved our solar system.

In a study published today in Science, the team shows the number of asteroid impacts on the Moon and Earth increased by two to three times starting around 290 million years ago.

“Our research provides evidence for a dramatic change in the rate of asteroid impacts on both Earth and the Moon that occurred around the end of the Paleozoic era,” said lead author Sara Mazrouei, who recently earned her PhD in the Department of Earth Sciences in the Faculty of Arts & Science at the University of Toronto (U of T). “The implication is that since that time we have been in a period of relatively high rate of asteroid impacts that is 2.6 times higher than it was prior to 290 million years ago.”

It had been previously assumed that most of Earth’s older craters produced by asteroid impacts have been erased by erosion and other geologic processes. But the new research shows otherwise.

“The relative rarity of large craters on Earth older than 290 million years and younger than 650 million years is not because we lost the craters, but because the impact rate during that time was lower than it is now,” said Rebecca Ghent, an associate professor in U of T’s Department of Earth Sciences and one of the paper’s co-authors. “We expect this to be of interest to anyone interested in the impact history of both Earth and the Moon, and the role that it might have played in the history of life on Earth.”

Scientists have for decades tried to understand the rate that asteroids hit Earth by using radiometric dating of the rocks around them to determine their ages. But because it was believed erosion caused some craters to disappear, it was difficult to find an accurate impact rate and determine whether it had changed over time.

A way to sidestep this problem is to examine the Moon, which is hit by asteroids in the same proportions over time as Earth. But there was no way to determine the ages of lunar craters until NASA’s Lunar Reconnaissance Orbiter (LRO) started circling the Moon a decade ago and studying its surface.

“The LRO’s instruments have allowed scientists to peer back in time at the forces that shaped the Moon,” said Noah Petro, an LRO project scientist based at NASA Goddard Space Flight Center.

Using LRO data, the team was able to assemble a list of ages of all lunar craters younger than about a billion years. They did this by using data from LRO’s Diviner instrument, a radiometer that measures the heat radiating from the Moon’s surface, to monitor the rate of degradation of young craters.

During the lunar night, rocks radiate much more heat than fine-grained soil called regolith. This allows scientists to distinguish rocks from fine particles in thermal images. Ghent had previously used this information to calculate the rate at which large rocks around the Moon’s young craters — ejected onto the surface during asteroid impact — break down into soil as a result of a constant rain of tiny meteorites over tens of millions of years. By applying this idea, the team was able to calculate ages for previously un-dated lunar craters.

When compared to a similar timeline of Earth’s craters, they found the two bodies had recorded the same history of asteroid bombardment.

“It became clear that the reason why Earth has fewer older craters on its most stable regions is because the impact rate was lower up until about 290 million years ago,” said William Bottke, an asteroid expert at the Southwest Research Institute in Boulder, Colorado and another of the paper’s coauthors. “The answer to Earth’s impact rate was staring everyone right in the face.”

The reason for the jump in the impact rate is unknown, though the researchers speculate it might be related to large collisions taking place more than 300 million years ago in the main asteroid belt between the orbits of Mars and Jupiter. Such events can create debris that can reach the inner solar system.

Ghent and her colleagues found strong supporting evidence for their findings through a collaboration with Thomas Gernon, an Earth scientist based at the University of Southampton in England who works on a terrestrial feature called kimberlite pipes. These underground pipes are long-extinct volcanoes that stretch, in a carrot shape, a couple of kilometers below the surface, and are found on some of the least eroded regions of Earth in the same places preserved impact craters are found.

“The Canadian shield hosts some of the best-preserved and best-studied of this terrain — and also some of the best-studied large impact craters,” said Mazrouei.

Gernon showed that kimberlite pipes formed since about 650 million years ago had not experienced much erosion, indicating that the large impact craters younger than this on stable terrains must also be intact.

“This is how we know those craters represent a near-complete record,” Ghent said.

While the researchers weren’t the first to propose that the rate of asteroid strikes to Earth has fluctuated over the past billion years, they are the first to show it statistically and to quantify the rate.

“The findings may also have implications for the history of life on Earth, which is punctuated by extinction events and rapid evolution of new species,” said Ghent. “Though the forces driving these events are complicated and may include other geologic causes, such as large volcanic eruptions, combined with biological factors, asteroid impacts have surely played a role in this ongoing saga.

“The question is whether the predicted change in asteroid impacts can be directly linked to events that occurred long ago on Earth.”

The findings are described in the study “Earth and Moon impact flux increased at the end of the Paleozoic,” published in Science. Support for the research was provided by the National Science and Engineering Research Council of Canada, NASA’s Solar System Exploration Research Virtual Institute, and the Natural Environment Research Council of the United Kingdom.

Reference:
Sara Mazrouei, Rebecca R. Ghent, William F. Bottke, Alex H. Parker, Thomas M. Gernon. Earth and Moon impact flux increased at the end of the Paleozoic. Science, 2019 DOI: 10.1126/science.aar4058

Note: The above post is reprinted from materials provided by University of Toronto.

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