Mass Extinctions

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#31
So maybe it was a comet strike after all ...

Study supports theory of extraterrestrial impact
http://www.physorg.com/news/2012-03-the ... mpact.html
March 5th, 2012 in Space & Earth / Earth Sciences

This image shows the "tectonic" effects of the collision of one spherule with another during the cosmic impact. Credit: UCSB

A 16-member international team of researchers that includes James Kennett, professor of earth science at UC Santa Barbara, has identified a nearly 13,000-year-old layer of thin, dark sediment buried in the floor of Lake Cuitzeo in central Mexico. The sediment layer contains an exotic assemblage of materials, including nanodiamonds, impact spherules, and more, which, according to the researchers, are the result of a cosmic body impacting Earth.

These new data are the latest to strongly support of a controversial hypothesis proposing that a major cosmic impact with Earth occurred 12,900 years ago at the onset of an unusual cold climatic period called the Younger Dryas. The researchers' findings appear today in the Proceedings of the National Academy of Sciences.

Conducting a wide range of exhaustive tests, the researchers conclusively identified a family of nanodiamonds, including the impact form of nanodiamonds called lonsdaleite, which is unique to cosmic impact. The researchers also found spherules that had collided at high velocities with other spherules during the chaos of impact. Such features, Kennett noted, could not have formed through anthropogenic, volcanic, or other natural terrestrial processes. "These materials form only through cosmic impact," he said.

These images of single and twinned nanodiamonds show the atomic lattice framework of the nanodiamonds. Each dot represents a single atom. Credit: UCSB

The data suggest that a comet or asteroid –– likely a large, previously fragmented body, greater than several hundred meters in diameter –– entered the atmosphere at a relatively shallow angle. The heat at impact burned biomass, melted surface rocks, and caused major environmental disruption. "These results are consistent with earlier reported discoveries throughout North America of abrupt ecosystem change, megafaunal extinction, and human cultural change and population reduction," Kennett explained.

The sediment layer identified by the researchers is of the same age as that previously reported at numerous locations throughout North America, Greenland, and Western Europe. The current discovery extends the known range of the nanodiamond-rich layer into Mexico and the tropics. In addition, it is the first reported for true lake deposits.

This is James Kennett. Credit: University of California - Santa Barbara
In the entire geologic record, there are only two known continent-wide layers with abundance peaks in nanodiamonds, impact spherules, and aciniform soot. These are in the 65-million-year-old Cretaceous-Paleogene
boundary layer that coincided with major extinctions, including the dinosaurs and ammonites; and the Younger Dryas boundary event at 12,900 years ago, closely associated with the extinctions of many large North American animals, including mammoths, mastodons, saber-tooth cats, and dire wolves.

"The timing of the impact event coincided with the most extraordinary biotic and environmental changes over Mexico and Central America during the last approximately 20,000 years, as recorded by others in several regional lake deposits," said Kennett. "These changes were large, abrupt, and unprecedented, and had been recorded and identified by earlier investigators as a 'time of crisis.' "

More information: “New evidence from Central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis,” by Isabel Israde-Alcántara et al. PNAS, 2012.

Provided by University of California - Santa Barbara
 
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#32
Or maybe it wasn't...

No Love for Comet Wipeout
http://news.sciencemag.org/sciencenow/2 ... tml?ref=hp
by Sid Perkins on 23 April 2012, 3:05 PM | 5 Comments

It's in there. The purported markers of an extraterrestrial impact found in a dark layer of sediment at Murray Springs, Arizona (left), also appear in similar yet older layers elsewhere, including Chile's Atacama Desert (right), suggesting the markers are actually formed on Earth by natural processes.
Credit: Adapted from J. S. Pigati et al., PNAS Early Edition (2012)

Did a comet wipe out woolly mammoths and an ancient Indian culture almost 13,000 years ago? Geologists have fiercely debated the topic since 2007. Now a new study says an extraterrestrial impact wasn't to blame, though the scientists who originally proposed the impact idea still aren't convinced.

Three unexplained phenomena happened on Earth around 12,900 years ago. An extended cold spell known as the Younger Dryas cooled the world for 1300 years. Large creatures such as mammoths, mastodons, and their predators went extinct. And the Clovis culture—a group defined by the distinctive stone and bone tools that they manufactured, and presumed by many archaeologists to be the first inhabitants of the New World—suddenly disappeared.

In 2007, a team of researchers tried to tie together these seemingly disparate events to a single cause: an extraterrestrial object, possibly a comet, exploded above eastern Canada, they speculated. Their claimed evidence, which has been much disputed since it was first reported, included several types of "impact markers" sometimes found after an extraterrestrial object strikes Earth. These purported markers include unusual grains of a titanium-rich form of the mineral magnetite; tiny magnetic spherules; and elevated levels of iridium, a relatively rare element that's more common in extraterrestrial objects than in Earth's crust. The researchers found all of these markers embedded within unusual layers of dark, organic-rich sediments that scientists often call "black mats." These strata are the remains of ancient marshes and swamps, and at many sites across North America, especially in the American Southwest, black mats began accumulating at the beginning of the Younger Dryas, the researchers noted. Many paleontologists have noted that black mats are often a sort of dividing line between older sediments containing fossils of ice-age megafauna, and younger sediments that don't. And many archaeologists have observed that black mats seem to mark the demise of the Clovis culture, because the distinctive spear points that they produced are common in sediments below the layers but nonexistent above.

According to the 2007 comet-strike hypothesis, large amounts of heat generated by the explosion of the comet shattered and melted much of the region's ice sheet, suddenly flooding the North Atlantic with fresh water that interrupted ocean circulation, which in turn triggered an extended cold snap that wiped out the Clovis culture and polished off the last remaining ice age megafauna.

"It's an appealing idea because it links all of these things together," says Jeffrey Pigati, a geologist with the U.S. Geological Survey in Denver, who isn't a proponent of the comet-strike idea. Unfortunately for that hypothesis, he and his colleagues report online today in the Proceedings of the National Academy of Sciences, not all of the purported "impact markers" are produced solely by extraterrestrial objects striking Earth.

Pigati and his team studied black mats at 13 sites in the American Southwest and in the Atacama Desert of northern Chile—including some sites where the mats began accumulating 40,000 years ago. At 10 of the 13 sites, regardless of a site's age or location, the researchers found all three of the "impact markers" described in the 2007 study, says Pigati. Although those presumed markers had also been found at a site in Belgium, he notes, they probably wouldn't have dispersed to the South American sites he and his colleagues sampled in their new study, because effects of the purported impact likely would have been limited to the Northern Hemisphere.

Also, Pigati says, he and his team found supposed markers even at sites much older than 12,900 years—indicating that the purported impact couldn't have been the source of those markers. Finally, he notes, the ratios of the concentrations of several rare-earth elements and other trace elements, including iridium, in the spherules embedded in the black mats match those found in Earth's crust, not in extraterrestrial objects. Rather than coming from an extraterrestrial impact, the spherules were formed on Earth and then trapped in the ancient wetlands by natural processes, the team concludes. The dense spherules then sank to the base of the mat because they're heavier than other windblown dust, sand, and silt. The chemical composition and location of the spherules, as well as their presence in black mats of many different ages, are more easily explained by natural processes than by extraterrestrial impacts, the team contends.

But the new study has several flaws, says Richard Firestone, an isotopic chemist at Lawrence Berkeley National Laboratory in Berkeley, California, and a member of the team that originally proposed the impact hypothesis in 2007. For one thing, he notes, Pigati and his colleagues didn't use a scanning electron microscope to scrutinize the surface of the spherules—the only way to distinguish impact generated spherules, he says, that were melted at high temperatures and had a distinctive pattern inscribed on their surface as they splashed through the air, from the spherules commonly found in wetland sediments. Also, Firestone notes, Pigati's team didn't scrutinize all of the spherules, only the ones that were truly spherical—thus discarding many of the tiny markers that might have been generated by the impact, including teardrop-shaped blobs that cooled in midair as well as misshapen blobs that formed when one near-molten droplet bumped into another.

Pigati says he accepts Firestone's criticisms but stands by his team's findings and interpretations. "We admit in our paper that we can't disprove the impact hypothesis," he notes. "Our point is that some of the spherules and other markers [cited in the 2007 report] aren't uniquely produced by impacts."
 
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It Took Earth Ten Million Years to Recover from Greatest Mass Extinction
http://www.sciencedaily.com/releases/20 ... 153810.htm

New research reveals that it took some 10 million years for Earth to recover from the greatest mass extinction of all time, some 250 million years ago. (Credit: © byheaven / Fotolia)

ScienceDaily (May 27, 2012) — It took some 10 million years for Earth to recover from the greatest mass extinction of all time, latest research has revealed.

Life was nearly wiped out 250 million years ago, with only 10 per cent of plants and animals surviving. It is currently much debated how life recovered from this cataclysm, whether quickly or slowly.

Recent evidence for a rapid bounce-back is evaluated in a new review article by Dr Zhong-Qiang Chen, from the China University of Geosciences in Wuhan, and Professor Michael Benton from the University of Bristol. They find that recovery from the crisis lasted some 10 million years, as explained May 27 in Nature Geoscience.

There were apparently two reasons for the delay, the sheer intensity of the crisis, and continuing grim conditions on Earth after the first wave of extinction.

The end-Permian crisis, by far the most dramatic biological crisis to affect life on Earth, was triggered by a number of physical environmental shocks -- global warming, acid rain, ocean acidification and ocean anoxia. These were enough to kill off 90 per cent of living things on land and in the sea.

Dr Chen said: "It is hard to imagine how so much of life could have been killed, but there is no doubt from some of the fantastic rock sections in China and elsewhere round the world that this was the biggest crisis ever faced by life."

Current research shows that the grim conditions continued in bursts for some five to six million years after the initial crisis, with repeated carbon and oxygen crises, warming and other ill effects.

Some groups of animals on the sea and land did recover quickly and began to rebuild their ecosystems, but they suffered further setbacks. Life had not really recovered in these early phases because permanent ecosystems were not established.

Professor Benton, Professor of Vertebrate Palaeontology at the University of Bristol, said: "Life seemed to be getting back to normal when another crisis hit and set it back again. The carbon crises were repeated many times, and then finally conditions became normal again after five million years or so."

Finally, after the environmental crises ceased to be so severe, more complex ecosystems emerged. In the sea, new groups, such as ancestral crabs and lobsters, as well as the first marine reptiles, came on the scene, and they formed the basis of future modern-style ecosystems.

Professor Benton added: "We often see mass extinctions as entirely negative but in this most devastating case, life did recover, after many millions of years, and new groups emerged. The event had re-set evolution. However, the causes of the killing -- global warming, acid rain, ocean acidification -- sound eerily familiar to us today. Perhaps we can learn something from these ancient events."

Story Source:

The above story is reprinted from materials provided by University of Bristol.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Zhong-Qiang Chen, Michael J. Benton. The timing and pattern of biotic recovery following the end-Permian mass extinction. Nature Geoscience, 2012; DOI: 10.1038/ngeo1475
 
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#34
And a new report says it was an extraterrestrial impact.

New evidence supporting theory of extraterrestrial impact found
http://phys.org/news/2012-06-evidence-t ... mpact.html
June 11th, 2012 in Space & Earth / Earth Sciences

These are microscopic images of grains of melted quartz from the YDB cosmic impact layer at Abu Hureyra, Syria, showing evidence of burst bubbles and flow textures that resulted from the melting and boiling of rock at very high temperatures. (Light microscope image at left; SEM image at right.) Credit: UCSB

An 18-member international team of researchers that includes James Kennett, professor of earth science at UC Santa Barbara, has discovered melt-glass material in a thin layer of sedimentary rock in Pennsylvania, South Carolina, and Syria. According to the researchers, the material –– which dates back nearly 13,000 years –– was formed at temperatures of 1,700 to 2,200 degrees Celsius (3,100 to 3,600 degrees Fahrenheit), and is the result of a cosmic body impacting Earth.

These new data are the latest to strongly support the controversial Younger Dryas Boundary (YDB) hypothesis, which proposes that a cosmic impact occurred 12,900 years ago at the onset of an unusual cold climatic period called the Younger Dryas. This episode occurred at or close to the time of major extinction of the North American megafauna, including mammoths and giant ground sloths; and the disappearance of the prehistoric and widely distributed Clovis culture. The researchers' findings appear today in the Proceedings of the National Academy of Sciences.

"These scientists have identified three contemporaneous levels more than 12,000 years ago, on two continents yielding siliceous scoria-like objects (SLO's)," said H. Richard Lane, program director of National Science

Foundation's Division of Earth Sciences, which funded the research. "SLO's are indicative of high-energy cosmic airbursts/impacts, bolstering the contention that these events induced the beginning of the Younger Dryas. That time was a major departure in biotic, human and climate history."

Morphological and geochemical evidence of the melt-glass confirms that the material is not cosmic, volcanic, or of human-made origin. "The very high temperature melt-glass appears identical to that produced in known cosmic impact events such as Meteor Crater in Arizona, and the Australasian tektite field," said Kennett.

"The melt material also matches melt-glass produced by the Trinity nuclear airburst of 1945 in Socorro, New Mexico," he continued. "The extreme temperatures required are equal to those of an atomic bomb blast, high enough to make sand melt and boil."

These are photos of melt glass known as trinitite formed at the ground surface from the melting of sediments and rocks by the very high temperatures of the Trinity nuclear airburst in New Mexico in 1945. This material is very similar to the glassy melt materials now reported from the cosmic impact YDB layer, consistent with the very high temperature origin of the melt materials in the YDB layer. Credit: UCSB

The material evidence supporting the YDB cosmic impact hypothesis spans three continents, and covers nearly one-third of the planet, from California to Western Europe, and into the Middle East. The discovery extends the range of evidence into Germany and Syria, the easternmost site yet identified in the northern hemisphere. The researchers have yet to identify a limit to the debris field of the impact.

"Because these three sites in North America and the Middle East are separated by 1,000 to 10,000 kilometers, there were most likely three or more major impact/airburst epicenters for the YDB impact event, likely caused by a swarm of cosmic objects that were fragments of either a meteorite or comet," said Kennett.

The PNAS paper also presents examples of recent independent research that supports the YDB cosmic impact hypothesis, and supports two independent groups that found melt-glass in the YDB layers in Arizona and Venezuela. "The results strongly refute the assertion of some critics that 'no one can replicate' the YDB evidence, or that the materials simply fell from space non-catastrophically," Kennett noted.

He added that the archaeological site in Syria where the melt-glass material was found –– Abu Hureyra, in the Euphrates Valley –– is one of the few sites of its kind that record the transition from nomadic hunter-gatherers to farmer-hunters who live in permanent villages. "Archeologists and anthropologists consider this area the 'birthplace of agriculture,' which occurred close to 12,900 years ago," Kennett said.

"The presence of a thick charcoal layer in the ancient village in Syria indicates a major fire associated with the melt-glass and impact spherules 12,900 years ago," he continued. "Evidence suggests that the effects on that settlement and its inhabitants would have been severe."

Provided by University of California - Santa Barbara
 
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#35
Or maybe it did.

Case Closed? Comet Crash Killed Ice Age Beasts
http://www.space.com/17676-comet-crash-ice-age.html

Megan Gannon, News Editor
Date: 19 September 2012 Time: 03:18 PM ET

Spherules from archaeological sites in the study. The microscopic particles have marred surface patterns from being crystallized in a molten state and then rapidly cooled.
CREDIT: University of South Carolina

A space rock crashed into Earth about 12,900 years ago, wiping out some of North America's biggest beasts and ushering in a period of extreme cooling, researchers say, based on new evidence supporting this comet-crash scenario.

If such an impact took place, it did not leave behind any obvious clues like a crater. But microscopic melted rock formations called spherules and nano-size diamonds in ancient soil layers could be telltale signs of a big collision. The mix of particles could only have formed under extreme temperatures, created by a comet or asteroid impact.

Researchers first reported in 2007 that these particles were found at several archaeological sites in layers of sediment 12,900 years old. Now an independent study published in the Sept.17 issue of the Proceedings of the National Academy of Sciences (PNAS) says those findings hold up.


A team led by Malcolm LeCompte, of Elizabeth City State University in North Carolina, studied sediment samples from three sites in the Unites States: Blackwater Draw in New Mexico, Topper in South Carolina, and Paw Paw Cove in Maryland. The researchers said they found the same microscopic spherules in some of the same ancient layers as were found in the 2007 study.

A comet crash in the ice fields of eastern Canada could explain the region's die-off during the late Pleistocene epoch. While the cause of the catastrophic extinction event has been debated, researchers say it killed off three-fourths of North America's large ice-age animals, such as saber-toothed tigers and woolly mammoths, and the Clovis people, a Stone Age group that had only recently immigrated to the continent. [Album: 25 Amazing Ancient Beasts]

In the PNAS study, researchers tested levels of Clovis artifacts at Topper for the microscopic soil clues. The Clovis are known for their large, fluted spear points that they likely used to hunt large animals and which were first found near Clovis, N.M.

"If debris was raining down from the atmosphere, the artifacts should have acted as a shield preventing spherules from accumulating in the layer underneath," University of South Carolina archaeologist Albert Goodyear said in a statement. "It turns out it really worked! There were up to 30 times more spherules at and just above the Clovis surface than beneath the artifacts."

There is debate over whether a comet impact actually wiped out the Clovis, with a study detailed in 2010 in the journal Current Anthropology, suggesting the Clovis' nomadic lifestyle, and not a demise, could explain gaps in their occupation of sites.

An impact also would explain what set off the Younger Dryas period or "Big Freeze," a 1,300-year era of glacial conditions that has been well documented in ocean cores and ancient soil samples. A comet would have produced enormous fires that melted large chunks of the North American ice sheet, sending cold water into the world's oceans and disrupting the circulation of currents responsible for global heat transport, the researchers noted.
 
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#36
Asteroid that killed the dinosaurs also wiped out the 'Obamadon'
December 10th, 2012 in Other Sciences / Archaeology & Fossils

In the foreground, the carnivorous lizard Palaeosaniwa stalks a pair of hatchling Edmontosaurus as the snake Cerberophis and the lizard Obamadon look on. In the background, an encounter between T. rex and Triceratops. (Artwork by Carl Buell)

The asteroid collision widely thought to have killed the dinosaurs also led to extreme devastation among snake and lizard species, according to new research—including the extinction of a newly identified lizard species Yale and Harvard scientists have named Obamadon gracilis.

"The asteroid event is typically thought of as affecting the dinosaurs primarily," said Nicholas R. Longrich, a postdoctoral associate with Yale's Department of Geology and Geophysics and lead author of the study. "But it basically cut this broad swath across the entire ecosystem, taking out everything. Snakes and lizards were hit extremely hard."

The study was scheduled for online publication the week of Dec. 10 in the Proceedings of the National Academy of Sciences.

Earlier studies have suggested that some snake and lizard species (as well as many mammals, birds, insects and plants) became extinct after the asteroid struck the earth 65.5 million years ago, on the edge of the Yucatan Peninsula. But the new research argues that the collision's consequences were far more serious for snakes and lizards than previously understood. As many as 83 percent of all snake and lizard species died off, the researchers said—and the bigger the creature, the more likely it was to become extinct, with no species larger than one pound surviving.

The results are based on a detailed examination of previously collected snake and lizard fossils covering a territory in western North America stretching from New Mexico in the southwestern United States to Alberta, Canada. The authors examined 21 previously known species and also identified nine new lizards and snakes.

They found that a remarkable range of reptile species lived in the last days of the dinosaurs. Some were tiny lizards. One snake was the size of a boa constrictor, large enough to take the eggs and young of many dinosaur species. Iguana-like plant-eating lizards inhabited the southwest, while carnivorous lizards hunted through the swamps and flood plains of what is now Montana, some of them up to six feet long.

"Lizards and snakes rivaled the dinosaurs in terms of diversity, making it just as much an 'Age of Lizards' as an 'Age of Dinosaurs,'" Longrich said.
The scientists then conducted a detailed analysis of the relationships of these reptiles, showing that many represented archaic lizard and snake families that disappeared at the end of the Cretaceous, following the asteroid strike.

One of the most diverse lizard branches wiped out was the Polyglyphanodontia. This broad category of lizards included up to 40 percent of all lizards then living in North America, according to the researchers. In reassessing previously collected fossils, they came across an unnamed species and called it Obamadon gracilis. In Latin, odon means "tooth" and gracilis means "slender."

"It is a small polyglyphanodontian distinguished by tall, slender teeth with large central cusps separated from small accessory cusps by lingual grooves," the researchers write of Obamadon, which is known primarily from the jaw bones of two specimens. Longrich said the creature likely measured less than one foot long and probably ate insects.

He said no one should impute any political significance to the decision to name the extinct lizard after the recently re-elected U.S. president: "We're just having fun with taxonomy."

The mass (but not total) extinction of snakes and lizards paved the way for the evolution and diversification of the survivors by eliminating competitors, the researchers said. There are about 9,000 species of lizard and snake alive today. "They didn't win because they were better adapted, they basically won by default, because all their competitors were eliminated," Longrich said.

Co-author Bhart-Anjan S. Bhullar, a doctoral student in organismic and evolutionary biology at Harvard University, said:

"One of the most important innovations in this work is that we were able to precisely reconstruct the relationships of extinct reptiles from very fragmentary jaw material. This had tacitly been thought impossible for creatures other than mammals. Our study then becomes the pilot for a wave of inquiry using neglected fossils and underscores the importance of museums like the Yale Peabody as archives of primary data on evolution—data that yield richer insights with each new era of scientific investigation."
Jacques A. Gauthier, professor of geology and geophysics at Yale and curator of vertebrate paleontology and vertebrate zoology, is also an author.
More information: "Mass Extinction of Lizards and Snakes at the Cretaceous-Paleogene Boundary", PNAS, 2012.

Provided by Yale University

"Asteroid that killed the dinosaurs also wiped out the 'Obamadon'." December 10th, 2012.
http://phys.org/news/2012-12-asteroid-d ... madon.html
 
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#37
Or maybe it didn't. Really ping pong this.

Study Rebuts Hypothesis That Comet Attacks Ended 9,000-Year-Old Clovis Culture
http://www.sciencedaily.com/releases/20 ... 095314.htm

Arrow head. (Credit: © underb / Fotolia)

Jan. 30, 2013 — Rebutting a speculative hypothesis that comet explosions changed Earth's climate sufficiently to end the Clovis culture in North America about 13,000 years ago, Sandia lead author Mark Boslough and researchers from 14 academic institutions assert that other explanations must be found for the apparent disappearance.

"There's no plausible mechanism to get airbursts over an entire continent," said Boslough, a physicist. "For this and other reasons, we conclude that the impact hypothesis is, unfortunately, bogus."

In a December 2012 American Geophysical Union monograph, first available in January, the researchers point out that no appropriately sized impact craters from that time period have been discovered, nor have any unambiguously "shocked" materials been found.

In addition, proposed fragmentation and explosion mechanisms "do not conserve energy or momentum," a basic law of physics that must be satisfied for impact-caused climate change to have validity, the authors write.

Also absent are physics-based models that support the impact hypothesis. Models that do exist, write the authors, contradict the asteroid-impact hypothesizers.

The authors also charge that "several independent researchers have been unable to reproduce reported results" and that samples presented in support of the asteroid impact hypothesis were later discovered by carbon dating to be contaminated with modern material.

The Boslough trail

Boslough has a decades-long history of successfully interpreting the effects of comet and asteroid collisions.

His credibility was on the line on in July 1994 when Eos, the widely read newsletter of the American Geophysical Union, ran a front-page prediction by a Sandia National Laboratories team, led by Boslough, that under certain conditions plumes from the collision of comet Shoemaker-Levy 9 with the planet Jupiter would be visible from Earth.

The Sandia team -- Boslough, Dave Crawford, Allen Robinson and Tim Trucano -- were alone among the world's scientists in offering that possibility.

"It was a gamble and could have been embarrassing if we were wrong," said Boslough. "But I had been watching while Shoemaker-Levy 9 made its way across the heavens and realized it would be close enough to the horizon of Jupiter that the plumes would show." His reasoning was backed by simulations from the world's first massively parallel processing supercomputer, Sandia's Intel Paragon.

On the one hand, it was a chance to check the new Paragon's logic against real events, a shakedown run for the defense-oriented machine. On the other, it was a hold-your-breath prediction, a kind of Babe Ruth moment when the Babe is reputed to have pointed to the spot in the center field bleachers he intended to hit the next ball. No other scientists were willing to point the same way, partly due to previous failures in predicting the behavior of comets Kohoutek and Halley, and partly because most astronomers believed the plumes would be hidden behind Jupiter's bulk.

That the plumes indeed proved visible started Boslough on his own trajectory as a media touchstone for things asteroidal and meteoritic.

It didn't hurt that, when he stands before television cameras to discuss celestial impacts, his earnest manner, expressive gestures and extraterrestrial subject matter make him seem a combination of Carl Sagan and Luke Skywalker, or perhaps Tom Sawyer and Indiana Jones.

Standing in jeans, work shirt and hiking boots for the Discovery Channel at the site in Siberia where a mysterious explosion occurred 105 years ago, or discussing it at Sandia with his supercomputer simulations in bold colors on a big screen behind him, the rangy, 6-foot-3 Sandia researcher vividly and accurately explained why the mysterious explosion at Tunguska that decimated hundreds of square miles of trees and whose ejected debris was seen as far away as London most probably was caused neither by flying saucers drunkenly ramming a hillside (a proposed hypothesis) nor by an asteroid striking the Earth's surface, but rather by the fireball of an asteroid airburst -- an asteroid exploding high above ground, like a nuclear bomb, compressed to implosion as it plunged deeper into Earth's thickening, increasingly resistive atmosphere. The governing physics, he said, was precisely the same as for the airburst on Jupiter.

Among later triumphs, Boslough was the Sandia component of a National Geographic team flown to the Libyan Desert to make sense of strange yellow-green glass worn as jewelry by pharaohs in days past. Boslough's take: It was the result of heat on desert sands from a hypervelocity impact caused by an even bigger asteroid burst.

In the present case

In the Clovis case, Boslough felt that his ideas were taken further than he could accept when other researchers claimed that the purported demise of Clovis civilization in North America was the result of climate change produced by a cluster of comet fragments striking Earth.

In a widely reported press conference announcing the Clovis comet hypothesis in 2007, proponents showed a National Geographic animation based on one of Boslough's simulations as inspiration for their idea.

Indiana Jones-style, Boslough responded. Confronted by apparently hard asteroid evidence, as well as a Nova documentary and an article in the journal Science, all purportedly showing his error in rebutting the comet hypothesis, Boslough ordered carbon dating of the major evidence provided by the opposition: nanodiamond-bearing carbon spherules associated with the shock of an asteroid's impact. The tests found the alleged 13,000-year-old carbon to be of very recent formation.

While this raised red flags to those already critical of the impact hypothesis, "I never said the samples were salted," Boslough said carefully. "I said they were contaminated."

That find, along with irregularities reported in the background of one member of the opposing team, was enough for Nova to remove the entire episode from its list of science shows available for streaming, Boslough said.

"Just because a culture changed from Clovis to Folsom spear points didn't mean their civilization collapsed," he said. "They probably just used another technology. It's like saying the phonograph culture collapsed and was replaced by the iPod culture."

Story Source:

The above story is reprinted from materials provided by DOE/Sandia National Laboratories.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

M. Boslough, K. Nicoll, V. Holliday, T. L. Daulton, D. Meltzer, N. Pinter, A. C. Scott, T. Surovell, P. Claeys, J. Gill, F. Paquay, J. Marlon, P. Bartlein, C. Whitlock, D. Grayson, and A. J. T. Jull. Arguments and Evidence Against a Younger Dryas Impact Event. Climates, Landscapes, and Civilizations, Geophysical Monograph Series, 2012; 198: 13-26 DOI: 10.1029/2012GM001209
 
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#38
Maybe there wasn't a comet impact.

What Caused a 1300-Year Deep Freeze?

Tools tell no tales. The disappearance of these early Native American artifacts was apparently not due to an extraterrestrial impact.
Bill Whittacker/Iowa Office of the State Archaeologist/Creative Commons

Tools tell no tales. The disappearance of these early Native American artifacts was apparently not due to an extraterrestrial impact.

Things were looking up for Earth about 12,800 years ago. The last Ice Age was coming to an end, mammoths and other large mammals romped around North America, and humans were beginning to settle down and cultivate wild plants. Then, suddenly, the planet plunged into a deep freeze, returning to near-glacial temperatures for more than a millennium before getting warm again. The mammoths disappeared at about the same time, as did a major Native American culture that thrived on hunting them. A persistent band of researchers has blamed this apparent disaster on the impact of a comet or asteroid, but a new study concludes that the real explanation for the chill, at least, may lie strictly with Earth-bound events.

The study “pulls the rug out from under the contrived impact hypothesis quite nicely,” says Christian Koeberl, a geochemist at the University of Vienna. Most evidence for the extraterrestrial impact hypothesis, he says, was conjured up “out of thin air.”

The 1300-year big chill is known as the Younger Dryas, so-called because of the sudden worldwide appearance of the cold-weather flowering plant Dryas octopetala. A number of causes have been suggested, including changes in ocean currents due to melting glaciers and volcanic activity. In 2007, a diverse group of 26 researchers, led by nuclear chemist Richard Firestone of the Lawrence Berkeley National Laboratory in California, formally proposed what is known as the Younger Dryas impact hypothesis, in which one or more extraterrestrial bodies blew up over North America, leading to widespread wildfires and strewing sun-blocking dust and debris across the globe.

In a series of papers, Firestone and his colleagues claimed various kinds of evidence for the hypothesis, including deposits of the element iridium (rare on Earth but abundant in meteorites), microscopic diamonds (called nanodiamonds), and magnetic particles in deposits at sites supposedly dated to about 12,800 years ago. The notion was popularized in television documentaries and other coverage on the National Geographic Channel, History Channel, and the PBS program NOVA. These claims were sharply contested by some specialists in the relevant fields, however, who either did not detect such evidence or argued that the deposits had other causes than a cosmic impact. For example, some say that nanodiamonds are common in ordinary geological formations, and that magnetic particles could come from ordinary fires.

Now comes what some researchers consider the strongest attack yet on the Younger Dryas impact hypothesis. In a paper published online this week in the Proceedings of the National Academy of Sciences, a team led by David Meltzer, an archaeologist at Southern Methodist University, Dallas, in Texas, looks at the dating of 29 different sites in the Americas, Europe, and the Middle East in which impact advocates have reported evidence for a cosmic collision. They include sites in which sophisticated stone projectiles called Clovis points, used by some of the earliest Americans to hunt mammals beginning about 13,000 years ago, have been found, such as Chobot in Alberta, Canada, Murray Springs in Arizona, and Paw Paw Cove in Maryland; the site of Abu Hureyra in Syria, where evidence of plant-cultivating hunter-gatherers occurs; and sites in Greenland, Germany, Belgium, and the Netherlands where other evidence for an impact has been claimed. The team argues that when the quality and accuracy of the dating—which was based on radiocarbon and other techniques—is examined closely, only three of the 29 sites actually fall within the time frame of the Younger Dryas onset, about 12,800 years ago; the rest were probably either earlier or later by hundreds (and in one case, thousands) of years.

“The supposed Younger Dryas impact fails on both theoretical and empirical grounds,” says Meltzer, who adds that the popular appeal of the hypothesis is probably due to the way that it provides “simple explanations for complex problems.” Thus, “giant chunks of space debris clobbering the planet and wiping out life on Earth has undeniably broad appeal,” Meltzer says, whereas “no one in Hollywood makes movies” about more nuanced explanations, such as Clovis points disappearing because early Americans turned to other forms of stone tool technology as the large mammals they were hunting went extinct as a result of the changing climate or hunting pressure.

Maarten Blaauw, a paleoecologist at Queen’s University Belfast in the United Kingdom, finds the new work convincing. “It is vital to get the ages right,” he says, which “appears to have been lacking in the case of the [impact] papers” that Meltzer and his colleagues reanalyzed. “This paper should be read widely, and its lessons learned by the paleo community and by archaeologists.”

But impact proponents appear unmoved by the new study. “We still stand fully behind the [impact hypothesis], which is based on more than a confluence of dates,” Firestone says. “Radiocarbon dating is a perilous process,” he contends, adding that the presence of Clovis artifacts and mammoth bones just under the claimed iridium, nanodiamond, and magnetic sphere deposits is a more reliable indicator that an extraterrestrial event was responsible for their disappearance.
http://news.sciencemag.org/archaeology/ ... eep-freeze
 
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#39
Australia's deadly eruptions were reason for the first mass extinction

A Curtin University researcher has shown that ancient volcanic eruptions in Australia 510 million years ago significantly affected the climate, causing the first known mass extinction in the history of complex life.

Published in the journal Geology, Associate Professor Fred Jourdan from Curtin's Department of Applied Geology, along with colleagues from several Australian and international institutions, used radioactive dating techniques to precisely measure the age of the eruptions of the Kalkarindji volcanic province -- where lavas covered an area of more than 2 million square kilometres in the Northern Territory and Western Australia.

Dr Jourdan and his team were able to prove the volcanic province occurred at the same time as the Early-Middle Cambrian extinction from 510-511 million years ago -- the first extinction to wipe out complex multicellular life.
"It has been well-documented that this extinction, which eradicated 50 per cent of species, was related to climatic changes and depletion of oxygen in the oceans, but the exact mechanism causing these changes was not known, until now," Dr Jourdan said.

"Not only were we able to demonstrate that the Kalkarindji volcanic province was emplaced at the exact same time as the Cambrian extinction, but were also able to measure a depletion of sulphur dioxide from the province's volcanic rocks -- which indicates sulphur was released into the atmosphere during the eruptions.

"As a modern comparison, when the small volcano Pinatubo erupted in 1991, the resulting discharge of sulphur dioxide decreased the average global temperatures by a few tenths of a degree for a few years following the eruption.

"If relatively small eruptions like Pinatubo can affect the climate just imagine what a volcanic province with an area equivalent to the size of the state of Western Australia can do."

The team then compared the Kalkarindji volcanic province with other volcanic provinces and showed the most likely process for all the mass extinctions was a rapid oscillation of the climate triggered by volcanic eruptions emitting sulphur dioxide, along with greenhouse gases methane and carbon dioxide.
"We calculated a near perfect chronological correlation between large volcanic province eruptions, climate shifts and mass extinctions over the history of life during the last 550 million years, with only one chance over 20 billion that this correlation is just a coincidence," Dr Jourdan said.

Dr Jourdan said the rapid oscillations of the climate produced by volcanic eruptions made it difficult for various species to adapt, ultimately resulting in their demise. He also stressed the importance of this research to better understand our current environment.

"To comprehend the long-term climatic and biological effects of the massive injections of gas in the atmosphere by modern society, we need to recognise how climate, oceans and ecosytems were affected in the past," he said.

Journal Reference:
F. Jourdan, K. Hodges, B. Sell, U. Schaltegger, M. T. D. Wingate, L. Z. Evins, U. Soderlund, P. W. Haines, D. Phillips, T. Blenkinsop. High-precision dating of the Kalkarindji large igneous province, Australia, and synchrony with the Early-Middle Cambrian (Stage 4-5) extinction. Geology, 2014; 42 (6): 543 DOI: 10.1130/G35434.1

http://www.sciencedaily.com/releases/20 ... 124327.htm
 
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#40
... The first person to find evidence that Earth's history was punctuated by global extinctions was palaeontologist Jack Sepkoski, who studied species diversity across geological time.

As well as proposing a "big five" of mass extinction events, Sepkoski also found evidence of a smaller extinction peak slightly earlier in the Permian in marine organisms called foraminifera in what is now China. Although further evidence of extinctions around this time has been found, all of it was in the tropics, suggesting that the event was a regional, not global, affair.

But now David Bond of the University of Hull, UK, says there is evidence of a major marine extinction at the same time in the Arctic. Brachiopods – hard-shelled marine animals – left the most visible evidence of their demise. The fossil record Bond has uncovered in Spitsbergen, Norway, and in Greenland suggests that more than 50 per cent of all marine genera died during the event, with some groups losing 80 per cent of their genera. Ammonites and corals suffered heavily. Bond reported his findings on 19 October to the Geological Society of America meeting in Vancouver, Canada. "We can now say this is a real global mass extinction," he says.

Because, on a geological scale, these two Permian extinctions occurred so close together, species numbers might not have had time to recover from the first before the second began, says Bond, and so whole groups of organisms might have been fatally weakened. For example, three-quarters of trilobite genera went extinct in the earlier Permian extinction, leaving only five surviving genera that were then wiped out at the end of the Permian. In contrast, other mass extinctions have been separated by at least 50 million years (see chart). ...

http://www.newscientist.com/article/mg2 ... E6DofmsW8k
 
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#41
...Some of Earth’s past mass extinctions have been caused by the impacts of extraterrestrial objects, such as the asteroid that struck near Mexico’s Yucatán Peninsula and wiped out the dinosaurs about 66 million years ago. Others have occurred during extended periods of geological disruption that include region-smothering volcanic eruptions. Both kinds of catastrophes seem to occur on a cycle of about 30 million years, notes Michael Rampino, a geoscientist at New York University in New York City. “It’s always been a mystery as to how extraterrestrial impacts could cause these long-lived geological effects,” he says. But invisible dark matter, he proposes, could trigger both extraterrestrial impacts and geological upheavals in one fell swoop.

Scientists still don’t know what dark matter is, but its gravitational pull on other objects in space shows that there’s a lot of it out there. Researchers estimate that in the plane of the galaxy, each square light-year contains about one solar mass of dark matter. Like the clouds of dust and gas that astronomers can see, clouds of dark matter may be perturbing the orbits of distant comets, causing them to fall into the inner solar system where they can strike Earth ...

http://news.sciencemag.org/earth/2015/02/did-dark-matter-kill-dinosaurs
 
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#42
Catastrophes that could end the world

THE eruption of Tambora 200 years ago was the largest volcanic blast of modern history, killing something like 100,000 people in what is today Indonesia, producing an ash cloud that covered a million square kilometres and temporarily changing the global climate. The veil of sulphate particles which Tambora created in the stratosphere cooled the planet’s continents by an average of about 2ºC in the following year; local changes were in some places much more severe, and there was agricultural chaos in North America, Europe and China. Volcanoes are nasty; other natural disasters—such as storms, floods and earthquakes—only have global effects because of the interconnectedness of human societies and economies, while large eruptions have direct geophysical effects worldwide. Yet volcanoes are not the only existential threats humanity faces. Which catastrophes could actually end human civilisation?

What would a Tambora-like eruption mean for the modern world?

A repeat of Tambora would have similar climatic effects, though it is possible that in today’s world their human impact would not be so severe. But the next large eruption could be a lot bigger than that. In terms of the volume of rock the eruption of the volcanic caldera at Taupo, in New Zealand, 26,500 years ago, was well over ten times the size of Tambora; that of Toba, in Indonesia, 75,000 years ago was almost 100 times larger than the 1815 blast. The area covered by ash from Toba to a depth of a centimetre or more has a population of about 2 billion people today. The climatic effects of an eruption do not increase linearly with its size, but if it arrived without years of warning (time to allow massive precautionary stockpiling) a repeat of the Toba eruption today would be a devastating blow to food security on a global scale and could be expected to cause tens of millions or hundreds of millions of casualties. Some researchers believe that the Toba eruption was sufficiently devastating to Homo sapiens, which may well then have been found at that time only in east Africa, as to almost wipe the species out. That could explain why modern humans have a very low level of genetic diversity compared with other apes.

The only other natural disasters of similar consequence are impacts by asteroids and comets, which can massively disrupt the climate in similar ways. ...

http://www.economist.com/blogs/econ...plains-10?fsrc=scn/tw/te/bl/ed/catastrophesEE
 

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#43
The Younger Dryas impact theory is once again 'in play' with the results of this new study. The key innovation in this story is the focus on wildfires triggered by the event. These researchers estimate the total Younger Dryas biomass burn-off exceeded that of the K-T / K-Pg boundary event that eliminated the dinosaurs.

New research suggests toward end of Ice Age, human beings witnessed fires larger than dinosaur killer, thanks to a cosmic impact
... On a ho-hum day some 12,800 years ago, the Earth had emerged from another ice age. Things were warming up, and the glaciers had retreated.

Out of nowhere, the sky was lit with fireballs. This was followed by shock waves.

Fires rushed across the landscape, and dust clogged the sky, cutting off the sunlight. As the climate rapidly cooled, plants died, food sources were snuffed out, and the glaciers advanced again. Ocean currents shifted, setting the climate into a colder, almost “ice age” state that lasted an additional thousand years.

Finally, the climate began to warm again, and people again emerged into a world with fewer large animals and a human culture in North America that left behind completely different kinds of spear points.

This is the story supported by a massive study of geochemical and isotopic markers just published in the Journal of Geology.

The results are so massive that the study had to be split into two papers.

“Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ~12,800 Years Ago” is divided into “Part I: Ice Cores and Glaciers” and “Part 2: Lake, Marine, and Terrestrial Sediments.” ...
FULL ARTICLE: https://news.ku.edu/2018/01/30/new-...-human-beings-witnessed-fires-larger-dinosaur

ABSTRACTS for the 2 papers:

http://www.journals.uchicago.edu/doi/full/10.1086/695703
http://www.journals.uchicago.edu/doi/full/10.1086/695704
 

AlchoPwn

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#44
I think we should hold a candle vigil for all the people killed in the Cambrian Explosion :bomb:
https://en.wikipedia.org/wiki/Cambrian_explosion
This appalling act of terror was clearly the work of hostile extraterrestrial forces intent on colonizing our planet.
Lest we forget. (what the Cambrian explosion was)
Too soon?
 
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#45
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Every cloud has a silver lining

A team of researchers from several institutions across the U.S. has found evidence suggesting that there was an explosion of diversity in fish after the end-Cretaceous mass extinction. In their paper published in the journal Nature Ecology and Evolution, the team describes their genetic study involving more than 1800 species of fish and what they found.

After the end-Cretaceous mass extinction—the one that killed off the dinosaurs—mammals became much more diverse and dominant. Without the dinosaurs to feast on them, they were free to prosper. Much less is known about what went on in the oceans. In this new effort, the researchers have added some new pieces to that puzzle.

Prior research has suggested that the asteroid or comet that smashed into the Earth approximately 65 million years ago killed off more than the dinosaurs—approximately 50 percent of all species worldwide disappeared. These include many sharks and other reptiles, leaving a void of sorts in the world's oceans that allowed fish to flourish. And flourish they did, according to the researchers with this new effort.

To learn more about what happened with sea creatures after the end-Cretaceous mass extinction, the researchers collected tissue samples from 118 acanthomorph species, looking specifically at 1,000 DNA sequences that were similar across the genomes of their samples—as part of that effort, they searched for variations in genetic sequences that offered clues regarding how closely related the fish were to one another.

https://phys.org/news/2018-03-genetic-explosion-diversity-fish-end-cretaceous.html





Read more at: https://phys.org/news/2018-03-genetic-explosion-diversity-fish-end-cretaceous.html#jCp
 

AlchoPwn

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Every cloud has a silver lining
A team of researchers from several institutions across the U.S. has found evidence suggesting that there was an explosion of diversity in fish after the end-Cretaceous mass extinction. In their paper published in the journal Nature Ecology and Evolution, the team describes their genetic study involving more than 1800 species of fish and what they found.
https://phys.org/news/2018-03-genetic-explosion-diversity-fish-end-cretaceous.html
Read more at: https://phys.org/news/2018-03-genetic-explosion-diversity-fish-end-cretaceous.html#jCp
In relationship to this topic, there are few things more fascinating and mysterious than the Cambrian Explosion. To this day science is still unable to understand the causes of the sudden upswing in genetic diversity that occurred. The payday for a discovery like that would be a Nobel Prize, with the likelihood of free superpowers, and I am only joking a little bit. You want Fortean? It has it all.
 
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#50
In relationship to this topic, there are few things more fascinating and mysterious than the Cambrian Explosion. To this day science is still unable to understand the causes of the sudden upswing in genetic diversity that occurred. The payday for a discovery like that would be a Nobel Prize, with the likelihood of free superpowers, and I am only joking a little bit. You want Fortean? It has it all.
But who planted the bomb?

Putin?

Or was it a black flag op?
 

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#51
I don't think it's fair to say that "science is unable to explain" the Cambrian explosion, so much as there are competing theories - which is what science is all about, really.

No offence to yourself, as it's not the context in which you used it, but I always find a phrase like "science is unable to explain" does scientists a disservice, and has a bit too much of an air of the E.L. Wisty-voiced "did you know..." pub bore to them!

I suppose the Cambrian explosion's closest comparison would be to the sudden emergence of flowering plants - things just ticking along quite nicely, then a sudden drastic change in so many directions at once.

The explanation I always remember hearing for the explosion was about changes in the amount of Oxygen in the atmosphere, though apparently that one's considered doubtful now, and it might be about a sudden increase in the levels of calcium in the ocean, meaning organisms were able to develop skeletons and so on.
 

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#52
The explanation I always remember hearing for the explosion was about changes in the amount of Oxygen in the atmosphere, though apparently that one's considered doubtful now, and it might be about a sudden increase in the levels of calcium in the ocean, meaning organisms were able to develop skeletons and so on.
The organisms that created the chalk sediments extracted CO2 from the biosphere and bound it into a solid form (chalk is calcium carbonate). This meant that oxygen became a larger proportion of the atmosphere as the CO2 was used up.
 

AlchoPwn

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#53
I don't think it's fair to say that "science is unable to explain" the Cambrian explosion, so much as there are competing theories - which is what science is all about, really.
No offence to yourself, as it's not the context in which you used it, but I always find a phrase like "science is unable to explain" does scientists a disservice, and has a bit too much of an air of the E.L. Wisty-voiced "did you know..." pub bore to them!
I suppose the Cambrian explosion's closest comparison would be to the sudden emergence of flowering plants - things just ticking along quite nicely, then a sudden drastic change in so many directions at once.
The explanation I always remember hearing for the explosion was about changes in the amount of Oxygen in the atmosphere, though apparently that one's considered doubtful now, and it might be about a sudden increase in the levels of calcium in the ocean, meaning organisms were able to develop skeletons and so on.
So... All of a sudden this planet experiences a sudden and inexplicable increase in the number of discrete species of life. These are often entirely bizarre creatures with odd numbers of limbs and lacking symmetry. It is, in effect the diametric opposite of what normally happens to life here, namely mass extinction events, or business as usual with species slowly evolving from prior versions. Out of nowhere in a tiny time frame in terms of evolution, suddenly there is a boom in living diversity that is unseen prior or since. Science says it could have been caused by variously, radiation, increased oxygen, or a major evolutionary advance such as vision. There is in fact no solid evidence to support any of these hypotheses. The most popular is the oxygen increase theory, but it is hotly debated, and I don't buy it. While skeletons definitely appear post Cambrian Explosion, the majority of organisms produced in the period still didn't develop skeletons, similarly there were plenty of predators prior too. In short, all the answers presented are wobbly in the extreme. Something caused a massive but apparently benign increase in species diversity and we don't know what it was with anything approaching certainty. In short "science is unable to explain" in any way that satisfies the scientific community itself.

TO INTERESTED PARTIES:
Here is a nice primer article for those who want in on the debate. It's great and has plenty of footnote links to increase your expertise in the field:
https://www.nature.com/news/what-sparked-the-cambrian-explosion-1.19379#/life
 
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#54
Here's another line of evidence supportive of the Younger Dryas Impact Hypothesis. A new study has found the first indications of a spike in African platinum residues from the time immediately preceding the Younger Dryas cooling. This new data, combined with similar results from other continents, is building the case for some sort of impact.
We Just Got More Evidence a Large Meteorite Smashed Into Earth 12,800 Years Ago

Just less than 13,000 years ago, the climate cooled for a short while in many parts of the world, especially in the northern hemisphere. We know this because of what has been found in ice cores drilled in Greenland, as well as from oceans around the world.

Grains of pollen from various plants can also tell us about this cooler period, which people who study climate prehistory call the Younger Dryas and which interrupted a warming trend after the last Ice Age. The term gets its name from a wildflower, Dryas octopetala.

It can tolerate cold conditions and was common in parts of Europe 12,800 years ago. At about this time a number of animals became extinct. These included mammoths in Europe, large bison in North America, and giant sloths in South America.

The cause of this cooling event has been debated a great deal. ... In 2007 Richard Firestone and other American scientists presented a new hypothesis: that the cause was a cosmic impact like an asteroid or comet.

The impact could have injected a lot of dust into the air, which might have reduced the amount of sunlight getting through the earth's atmosphere. This might have affected plant growth and animals in the food chain.

Research we have just had published sheds new light on this Younger Dryas Impact Hypothesis. We focus on what platinum can tell us about it. ...
FULL STORY: https://www.sciencealert.com/a-larg...-years-ago-and-caused-massive-climate-changes
 

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#55
Here's the abstract for this newly published study, which is available in its entirety at the link ...

The Younger Dryas interval at Wonderkrater (South Africa) in the context of a platinum anomaly
Thackeray, J. Francis; Scott, Louis; Pieterse, P
URI: https://hdl.handle.net/10539/28129
Date: 2019-10-02

Abstract:

Wonderkrater in the Limpopo Province in South Africa is a late Quaternary archaeological site with peat deposits extending back more than 30 000 years before the present. Palaeoclimatic indices based on multivariate analysis of pollen spectra reflect a decline in temperature identifiable with the Younger Dryas (YD). A prominent spike in platinum is documented in aWonderkrater sample (5614) with a mean date of 12 744 cal yr BP using a Bayesian model, preceding the onset of the YD cooling event. The YD platinum spike at Wonderkrater is the first to be observed in Africa in the southern hemisphere, supplementing new discoveries from Patagonia in South America, in addition to more than 25 sites with such platinum anomalies in the northern hemisphere. The observations from South Africa serve to strengthen ongoing assessments of the controversial YD Impact Hypothesis, whereby it is proposed that a meteorite or cometary impact contributed to a decline in temperature, associated inter alia with dispersion of atmospheric dust, mammalian extinctions and cultural changes.

SOURCE: http://wiredspace.wits.ac.za/handle/10539/28129
 

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#56
Did an extraterrestrial impact trigger the extinction of ice-age animals?

Archaeologist finds evidence in South Carolina to support controversial theory

Date: October 25, 2019
Source: University of South Carolina

Based on research at White Pond near Elgin, South Carolina, archaeologists present new evidence of a controversial theory that suggests an extraterrestrial body crashing to Earth almost 13,000 years ago caused the extinction of many large animals and a probable population decline in early humans.

https://www.sciencedaily.com/releases/2019/10/191025110314.htm
 

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#57
Bad luck may have caused Neanderthals' extinction – study

Source: The Guardian online
Date: 27 November, 2019

Perhaps it wasn’t our fault after all: research into the demise of the Neanderthals has found that rather than being outsmarted by Homo sapiens, our burly, thick-browed cousins may have gone extinct through bad luck alone.

The Neanderthal population was so small at the time modern humans arrived in Europe and the Near East that inbreeding and natural fluctuations in birth rates, death rates and sex ratios could have finished them off, the scientists claim.

https://www.theguardian.com/science...may-have-caused-neanderthals-extinction-study
 

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#58
Scientists re-counted Australia's extinct species, and the result is devastating

Source: theconservation.com
Date: 2 December, 2019

It’s well established that unsustainable human activity is damaging the health of the planet. The way we use Earth threatens our future and that of many animals and plants. Species extinction is an inevitable end point.

It’s important that the loss of Australian nature be quantified accurately. To date, putting an exact figure on the number of extinct species has been challenging. But in the most comprehensive assessment of its kind, our research has confirmed that 100 endemic Australian species living in 1788 are now validly listed as extinct.

Alarmingly, this tally confirms that the number of extinct Australian species is much higher than previously thought.

https://theconversation-com.cdn.amp...3A%2F%2Fwww.google.com&amp_tf=From%20%251%24s
 

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#59
Isn't that really just a small percentage compared to the known animal and plant species that are at an underestimate at 28k? My point being that it isn't as apocalyptic as the headline and we can do more in the future to learn and remedy.
 
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