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rynner2

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Ice Age blast 'ravaged America'

A controversial new idea suggests that a large space rock exploded over North America 13,000 years ago.
The blast may have wiped out one of America's first Stone Age cultures as well as the continent's big mammals such as the mammoth and the mastodon.

The blast, from a comet or asteroid, caused a major bout of climatic cooling which may also have affected human cultures emerging in Europe and Asia.

Scientists will outline their evidence this week at a meeting in Mexico.

The evidence comes from layers of sediment at more than 20 sites across North America.

These sediments contain exotic materials: tiny spheres of glass and carbon, ultra-small specks of diamond - called nanodiamond - and amounts of the rare element iridium that are too high to have come from Earth.

All, they argue, point to the explosion 12,900 years ago of an extraterrestrial object up to 5km across.

No crater remains, possibly because the Laurentide Ice Sheet, which blanketed thousands of sq km of North America during the last Ice Age, was thick enough to mask the impact.

Another possibility is that it exploded in the air.

Climate cooling

The rocks studied by the researchers have a black layer which, they argue, is the charcoal deposited by wildfires which swept the continent after the explosion.

The blast would not only have generated enormous amounts of heat that could have given rise to wildfires, but also brought about a period of climate cooling that lasted 1,000 years - an event known as the Younger Dryas.

Professor James Kennett, from the University of California in Santa Barbara (UCSB), said the explosion could be to blame for the extinction of several large North American mammals at the end of the last Ice Age.

"All the elephants, including the mastodon and the mammoth, all the ground sloths, including the giant ground sloth - which, when standing on its hind legs, would have been as big as a mammoth," he told the BBC.

"All the horses went out, all the North American camels went out. There were large carnivores like the sabre-toothed cat and an enormous bear called the short-faced bear."

Professor Kennett said this could have had an enormous impact on human populations.

Population decline

According to the traditional view, humans crossed from north-east Asia to America at the end of the last Ice Age, across a land bridge which - at the time - connected Siberia to Alaska.

The Clovis culture was one of the earliest known cultures in the continent. These proficient hunter-gatherers developed a distinctive thin, fluted spear head known as the Clovis point, which is regarded as one of the most sophisticated stone tools ever developed.

Archaeologists have found evidence from the Topper site in South Carolina, US, that Clovis populations here went through a population collapse.

But there is no evidence of a similar decline in other parts of the continent. The Clovis culture does vanish from the archaeological record abruptly, but it is replaced by a myriad of different local hunter-gatherer cultures.

Jeff Severinghaus, a palaeoclimatologist at Scripps Institution of Oceanography in California, told Nature magazine: "Their impact theory shouldn't be dismissed; it deserves further investigation."

According to the new idea, the comet would have caused widespread melting of the North American ice sheet. The waters would have poured into the Atlantic, disrupting its currents.

This, they say, could have caused the 1,000 year-long Younger Dryas cold spell, which also affected Asia and Europe.

The Younger Dryas has been linked by some researchers to changes in the living patterns of people living in the Middle East which led to the beginning of farming.

A massive explosion near the Tunguska river, Siberia, in 1908, is also thought to have been caused by a space rock exploding in the atmosphere. It felled 80 million trees over an area of 2,000 sq km.

The new theory will be presented and debated at the American Geophysical Union's Joint Meeting in Acapulco, Mexico, this week.

http://news.bbc.co.uk/1/hi/sci/tech/6676461.stm
 
Diamond clues to beasts' demise
By Molly Bentley
Science reporter

The controversial idea that space impacts may have wiped out woolly mammoths and early human settlers in North America has received new impetus.

Nano-diamonds and other exotic impact materials have been unearthed in thin sediments, Science magazine reports.

The age of these materials coincides with the start of a millennium-long climate cooling event known as the Younger Dryas - some 13,000 years ago.

Many large animals vanish from the archaeological record at this time.

It is also the period in Earth history that sees the demise of Clovis culture - the prehistoric civilisation that many regard as the first human occupation of North America.

...Long article, so I've snipped out the middle chunk...

Critics say that with an impact comes a crater, such as at Chicxulub in the Yucatan, Mexico, which supports the theory that dinosaurs were wiped out by an asteroid impact 65 million years ago.

But an airburst in which an impactor explodes in the Earth's atmosphere - such as that over Tunguska, Siberia, in 1908 - might not produce a crater, said Dr James Kennett.

The energy released in the Tunguska blast was at least five megatons, said Dr West. The Younger Dryas impact would have been much larger.

"Imagine 1,000 to 10,000 atomic bombs detonating within a few minutes over two continents," he said.

Had the Clovis people witnessed the event, said Dr West, they would have seen a brilliant flash followed by others in quick succession.

The sky would be a canopy of fire, and shock waves would flatten trees. Miniscule diamonds would drizzle over tens of thousands of kilometres, a third of the way around the planet.

Nasa (Ames) space scientist David Morrison says the abundance of nano-diamonds is an "interesting mystery", but he does not think they were produced by cosmic airbursts.

A comet or asteroid that fragmented in Earth's atmosphere might have time to disperse over a few hundred kilometres, but certainly not thousands of kilometres across a continent, he said.

"I know of no mechanism that would break up a comet and distribute it over North America in the way they suggest," Dr Morrison told BBC News.

"It violates what we understand about cosmic impacts," he said.

Scepticism is necessary when building a new scientific theory. But, Dr West said, there was particular resistance to that of a Younger Dryas impact because the event occurred in modern human history and was so abrupt.

"People still like to think of geological processes happening slowly over time," he explained.

"It's unsettling that something happening in a few minutes could flip our climate and cause widespread extinctions."

http://news.bbc.co.uk/1/hi/sci/tech/7808171.stm
 
Comet Impact Theory Disproved

Understanding whether rapid changes in climate have caused wild fires in the past will help understand whether current changes in global temperatures will cause more frequent fires at the present time. Such fires have a major impact on the economy and health of the population, as well as feeding into the increase in global warming.

by Staff Writers
Bristol, UK (SPX) Jan 28, 2009
New data disproves the recent theory that a large comet exploded over North America 12,900 years ago, causing a shock wave that travelled across North America at hundreds of kilometres per hour and triggering continent-wide wildfires.

Dr Sandy Harrison from the University of Bristol and colleagues tested the theory by examining charcoal and pollen records to assess how fire regimes in North America changed between 15 and 10,000 years ago, a time of large and rapid climate changes.

Their results provide no evidence for continental-scale fires, but support the fact that the increase in large-scale wildfires in all regions of the world during the past decade is related to an increase in global warming.

Fire is the most ubiquitous form of landscape disturbance and has important effects on climate through the global carbon cycle and changing atmospheric chemistry. This has triggered an interest in knowing how fire has changed in the past, and particularly how fire regimes respond to periods of major warming.

The end of the Younger Dryas, about 11,700 years ago, was an interval when the temperature of Greenland warmed by over 5 degrees C in less than a few decades. The team used 35 records of charcoal accumulation in lake sediments from sites across North America to see whether fire regimes across the continent showed any response to such rapid warming.

They found clear changes in biomass burning and fire frequency whenever climate changed abruptly, and most particularly when temperatures increased at the end of the Younger Dryas cold phase. The results published, January 26, in the Proceedings of the National Academy of Science.

Understanding whether rapid changes in climate have caused wild fires in the past will help understand whether current changes in global temperatures will cause more frequent fires at the present time. Such fires have a major impact on the economy and health of the population, as well as feeding into the increase in global warming.

http://www.spacedaily.com/reports/Comet ... d_999.html
 
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Lake Sediments Cast More Doubt That a Comet Caused Ice Age Extinctions

Overhunting by Clovis people over centuries, not a catastrophic impact, may have wiped out North American mammoths and other megafauna, researchers say
By Brendan Borrell

ALBUQUERQUE—After combing through layers of ancient lake sediments, paleoecologist Jacquelyn Gill of the University of Wisconsin–Madison says her team has found no evidence to support a controversial comet theory for an ice age extinction event.

"There's no physical trend to suggest that there was an impact event," Gill said Tuesday at the Ecological Society of America meeting held here this week. "If there was an impact event...it's not having the ecological effects [previously] suggested."

In 2007 Richard Firestone at the Lawrence Berkeley National Laboratory and colleagues published evidence suggesting that a comet exploding in the atmosphere 12,900 years ago near the Great Lakes set off massive fires in North America. These fires supposedly led to the rapid disappearance of the continent's Clovis culture as well as megafauna including mammoths, ground sloths and 33 other large mammal genera.

But skeptics point to the fact that no associated impact craters have been found, and evidence for continental forest fires and a rapid decline in human populations is sketchy. Besides, if such an episode had occurred, small mammals and birds somehow survived. (Another recent study has called into question the likelihood of comet impacts being responsible for more than one extinction event during Earth's history.)

Gill and her team decided to look for hints of the comet's impact not on land but in three lakes in Indiana and Ohio, where pollen and minerals have settled daily, creating an ecological record dating back millennia. She scoured core samples for evidence of ash, charcoal, magnetic grains, tiny silicate spheres, and elements such as titanium and chromium that could be associated with impact events. She did not look for rare earth minerals like iridium, which other researchers rely on as a signature of impacts.

The team failed to find a consistent signal that would indicate that a single catastrophe occurred around 12,900 years ago. At one lake, titanium actually decreased at the same time charcoal was increasing. "It's clearly not an impact event," Gill said.

Gill also questioned the view that animals died off right at the time of the proposed impact event.

Fungal spores called Sporormiella, associated with the dung of large mammals, actually begin to decline 14,600 years ago, soon after the end of the last ice age. The spores wink out of the record at one lake 13,600 years ago and only recover in the past few centuries with the rise in cattle grazing. At the same time, pollen from the plants that megafauna munched on—ash, ironwood and hop hornbeam—starts piling up, suggesting the plants' growth was no longer being kept in check by leaf-loving large mammals.

More recent megafauna fossils, dated between 13,600 and 12,900 years ago, were likely the last hangers-on as the Clovis people decimated species with their characteristic spears, Gill says.

But Firestone was not swayed by the new study, which he says "adds nothing to the argument." He says that he would not expect to find much evidence in lake sites because magnetic material would rust away, while the tiny spheres float and would not collect on the lake bottom. For him, the data still points toward an extraterrestrial impact. "As far as I'm concerned the debate is settled," he said.

http://www.scientificamerican.com/artic ... met-doubts
 
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North America comet theory questioned

No evidence of an extraterrestrial impact 13,000 years ago, studies say.

Rex Dalton

An independent study has cast more doubt on a controversial theory that a comet exploded over icy North America nearly 13,000 years ago, wiping out the Clovis people and many of the continent's large animals.


Sediments at the San Jon site, in eastern New Mexico, contained very low abundances of magnetic spherules said to be evidence of an impact.Vance HollidayArchaeologists have examined sediments at seven Clovis-age sites across the United States, and did not find enough magnetic cosmic debris to confirm that an extraterrestrial impact happened at that time, says the report in the Proceedings of the National Academy of Sciences (PNAS)1. It is the latest of several studies unable to support aspects of the impact hypothesis.

In 2007, a team led by Californian researchers announced a theory2 that a comet or asteroid had exploded over the North American ice sheet, creating widespread fire and an atmospheric soot burst followed by a cooling period known as the Younger Dryas. Sometime after this, the Clovis people, sophisticated large-animal hunters known for their spear points, mysteriously disappeared; the team linked their vanishing to the environmental effects of the proposed impact.

Key evidence came in the form of magnetic microspherules discovered in sediments at 25 locations, including eight Clovis-age sites. Richard Firestone, of Lawrence Berkeley National Laboratory in California, and his colleagues argued that the microspherules were remnants of cosmic debris from an explosion.

But in more than 18 months of sedimentary analysis, a team led by Todd Surovell, an archaeologist at the University of Wyoming in Laramie, was unable to detect microspherule peaks. Two of the seven sites the group studied were places where Firestone's team identified spherule peaks.

"I spent hundreds of hours at the microscope examining sediment samples," says Surovell, "and I didn't find any physical evidence to support their theory."

Standing firm
The other team isn't backing down. "Their study doesn't negate our hypothesis," says James Kennett, a palaeoceanographer at the University of California at Santa Barbara and one of Firestone's co-authors. Another co-author, avocational geophysicist Allen West of Prescott, Arizona, says that Surovell's group didn't use the correct technique to extract, identify and quantify the microspherules.

Several other groups have been unable to support important aspects of the comet theory.

In a PNAS article published in February3, Jennifer Marlon, a doctoral geography student at the University of Oregon in Eugene, and her colleagues found no systematic burning of biomass — as would have occurred if continent-wide fires had happened — at the time of the Younger Dryas in pollen and charcoal records at 35 sites. And at the Ecological Society of America meeting in Albuquerque, New Mexico, in August, Jacquelyn Gill, a palaeoecology doctoral student at the University of Wisconsin-Madison, reported finding no evidence of massive burning in sediment cores taken from lake beds in Ohio and Indiana. ...

Kennett, however, calls these studies "flawed". In August, his team published a report4 saying they had found nanometre-sized diamonds, purportedly created during an impact, and soot in sediments dated to the Younger Dryas on Santa Rosa Island, off the coast of California.

More studies of the theory — both critical and supportive — are in the publishing pipelines at other journals.

Surovell's co-author Vance Holliday, an archaeologist at the University of Arizona in Tucson, and his colleagues have an article in press at Current Anthropology that says the archaeological and geochronological records don't support a collapse of Clovis people at the time of the purported impact.

References
Surovell, T. A. et al. Proc. Natl Acad. Sci. USA advance online publication doi:10.1073/pnas.0907857106 (2009).
Firestone, R. B. et al. Proc. Natl Acad. Sci. USA 104, 16016-16021 (2007). | Article | PubMed
Marlon, J. R. et al. Proc. Natl Acad. Sci. USA 106, 2519-2524 (2009). | Article | PubMed
Kennett, D. J. et al. Proc. Natl Acad. Sci. USA 106, 12623-12628 (2009). | Article | PubMed

http://www.nature.com/news/2009/091012/ ... 9.997.html
 
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Yet more on the non-comet.

Was there a Stone Age apocalypse or not?
http://www.newscientist.com/article/dn1 ... r-not.html
19:00 19 November 2009 by Jeff Hecht

Was there a Stone Age apocalypse or not? One narrative has it that about 13,000 years ago a comet blasted North America, wiping out the continent's megafauna – as well as its early settlers.

It's a compelling story, offering a simple explanation to the mystery of why mammoths, mastodons, and Clovis humans vanished. But it's a controversial theory, and new research suggests the impact was far too small to have done any serious damage.

Doubts centre on the speed of extinctions, the fate of the Clovis culture, and the presence of supposed impact signatures. But advocates of the comet-blast theory say they will present their own new data at the American Geophysical Union (AGU) meeting in San Francisco, where they will share the stage with sceptics.

"Nothing special happened at 12,900 years ago," says John Williams of the University of Wisconsin-Madison. His data, reported in Science this week, suggest that large mammals were already rare well before the purported impact.

Scraping the bottom
Williams and his colleagues searched layered lake-bottom deposits in Indiana and New York State for the spores of the fungus Sporormiella found in the dung of large plant-eating mammals such as mammoths and horses.

From a decline in the spore counts, they conclude that the megafauna population dropped steadily between 14,800 and 13,700 years ago, making them rare 800 years before any comet strike. Williams says the data rule out a sudden, impact-driven extinction.

However, geologist and impact-advocate James Kennett at the University of California, Santa Barbara, calls that "a classic case of over-interpretation" because the data comes from only a small area and not from different sites across the whole of North America.

Cultural development
Some anthropologists are also unhappy and with the sudden extinction theory, taking issue with claims that an impact wiped out the Clovis people.

It's true that distinctive Clovis-style artefacts disappear and sites were abandoned at the start of a dramatic cooling event which began about 13,000 years ago called the Younger Dryas. But the people didn't die, says Vance Holliday of the University of Arizona in Tucson. "An artefact style was replaced by another style. You see that all over the world." Moreover, early North Americans were highly mobile hunter-gatherers who occupied sites only briefly before moving on.

What's more, the geological layer representing the Younger Dryas is missing the sort of extraterrestrial material that was a hallmark of the impact that wiped out the dinosaurs.

Comet conundrum
Isotope geochemist Mukul Sharma of Dartmouth College in Hanover, New Hampshire, says he has been unable to find any significant amount of platinum-group elements with the distinctive isotopic signature showing that they came from space. Sharma will detail his findings at the AGU meeting.

Yet something did crash into the Pacific Ocean around the period in question. In a separate AGU paper, Sharma will report finding traces of extraterrestrial osmium on the floor of the mid-Pacific dating from between 16,000 and 8000 years ago.

Some Younger Dryas deposits do contain residues similar to those from the 1908 Tunguska explosion over Siberia, says Adrian Melott of the University of Kansas, Lawrence. He reckons the North American event was "something maybe a couple of orders of magnitude bigger than Tunguska" – but still perhaps only one-hundredth the scale of the proposed comet blast.

Journal reference: Science, DOI: 10.1126/science.1179504
 
No Evidence for Clovis Comet Catastrophe, Archaeologists Say

These are Clovis Points. (Credit: David Meltzer)

ScienceDaily (Oct. 1, 2010) — New research challenges the controversial theory that an ancient comet impact devastated the Clovis people, one of the earliest known cultures to inhabit North America.

Writing in the October issue of Current Anthropology, archaeologists Vance Holliday (University of Arizona) and David Meltzer (Southern Methodist University) argue that there is nothing in the archaeological record to suggest an abrupt collapse of Clovis populations. "Whether or not the proposed extraterrestrial impact occurred is a matter for empirical testing in the geological record," the researchers write. "Insofar as concerns the archaeological record, an extraterrestrial impact is an unnecessary solution for an archaeological problem that does not exist."

The comet theory first emerged in 2007 when a team of scientists announced evidence of a large extraterrestrial impact that occurred about 12,900 years ago. The impact was said to have caused a sudden cooling of the North American climate, killing off mammoths and other megafauna. It could also explain the apparent disappearance of the Clovis people, whose characteristic spear points vanish from the archaeological record shortly after the supposed impact.

As evidence for the rapid Clovis depopulation, comet theorists point out that very few Clovis archaeological sites show evidence of human occupation after the Clovis. At the few sites that do, Clovis and post-Clovis artifacts are separated by archaeologically sterile layers of sediments, indicating a time gap between the civilizations. In fact, comet theorists argue, there seems to be a dead zone in the human archaeological record in North America beginning with the comet impact and lasting about 500 years.

But Holliday and Meltzer dispute those claims. They argue that a lack of later human occupation at Clovis sites is no reason to assume a population collapse. "Single-occupation Paleoindian sites -- Clovis or post-Clovis -- are the norm," Holliday said. That's because many Paleoindian sites are hunting kill sites, and it would be highly unlikely for kills to be made repeatedly in the exact same spot.

"So there is nothing surprising about a Clovis occupation with no other Paleoindian zone above it, and it is no reason to infer a disaster," Holliday said.

In addition, Holliday and Meltzer compiled radiocarbon dates of 44 archaeological sites from across the U.S. and found no evidence of a post-comet gap. "Chronological gaps appear in the sequence only if one ignores standard deviations (a statistically inappropriate procedure), and doing so creates gaps not just around [12,900 years ago] but also at many later points in time," they write.

Sterile layers separating occupation zones at some sites are easily explained by shifting settlement patterns and local geological processes, the researchers say. The separation should not be taken as evidence of an actual time gap between Clovis and post-Clovis cultures.

Holliday and Meltzer believe that the disappearance of Clovis spear points is more likely the result of a cultural choice rather than a population collapse. "There is no compelling data to indicate that North American Paleoindians had to cope with or were affected by a catastrophe, extraterrestrial or otherwise, in the terminal Pleistocene," they conclude.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by University of Chicago Press Journals, via EurekAlert!, a service of AAAS.

http://www.sciencedaily.com/releases/20 ... 171815.htm
 
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So maybe it was a comet strike after all ...

Study supports theory of extraterrestrial impact

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

http://www.physorg.com/news/2012-03-the ... mpact.html
 
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Or maybe it wasn't...

No Love for Comet Wipeout

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."

http://news.sciencemag.org/sciencenow/2 ... tml?ref=hp
 
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And a new report says it was an extraterrestrial impact.

New evidence supporting theory of extraterrestrial impact found

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

http://phys.org/news/2012-06-evidence-t ... mpact.html
 
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... ice-age paleo-climate change is potentially full of all sorts of unknown variables. Including meteor strikes.

http://www.sciencedaily.com/releases/2007/09/070924172959.htm

Extraterrestrial Impact Likely Source Of Sudden Ice Age Extinctions

ScienceDaily (Sep. 24, 2007) — At the end of the Pleistocene era, woolly mammoths roamed North America along with a cast of fantastic creatures – giant sloths, saber-toothed cats, camels, lions, tapirs and the incredible teratorn, a condor with a 16-foot wingspan.

About 12,900 years ago, these megafauna disappeared from the fossil record, as did evidence of human remains. The cause of the mass extinction and the human migration is a mystery. Now a team of scientists, including Brown University planetary geologist Peter Schultz, provides evidence that an asteroid impact likely caused the sudden climate changes that killed off the mammoths and other majestic beasts of prehistory.

In the Proceedings of the National Academy of Sciences, the international team lays out its theory that the mass extinctions in North America were caused by one or more extraterrestrial objects – comets or meteorites – that exploded over the Earth or slammed into it, triggering catastrophic climate change.

The scientists believe that evidence for these extraterrestrial impacts is hidden in a dark layer of dirt sometimes called a black mat. Found in more than 50 sites around North America, this puzzling slice of geological history is a mere three centimeters deep and filled with carbon, which lends the layer its dark color. This black mat has been found in archaeological digs in Canada and California, Arizona and South Carolina – even in a research site in Belgium.

The formation of this layer dates back 12,900 years and coincides with the abrupt cooling of the Younger Dryas period, sometimes called the “Big Freeze.” This coincidence intrigued the researchers, led by Richard Firestone of Lawrence Berkeley National Laboratory, who thought that the black mat might be related to the mass extinctions.

So the researchers studied black mat sediment samples from 10 archaeological sites dating back to the Clovis people, the first human inhabitants of the New World. Researchers conducted geochemical analysis of the samples to determine their makeup and also ran carbon dating tests to determine the age of the samples.

Directly beneath the black mat, researchers found high concentrations of magnetic grains containing iridium, charcoal, soot, carbon spherules, glass-like carbon containing nanodiamonds and fullerenes packed with extraterrestrial helium – all of which are evidence for an extraterrestrial impact and the raging wildfires that might have followed.

Schultz, professor of geological sciences at Brown and an impact specialist, said the most provocative evidence for an extraterrestrial impact was the discovery of nanodiamonds, microscopic bits of diamond formed only from the kind of intense pressure you’d get from a comet or meteorite slamming into the Earth.

“We don’t have a smoking gun for our theory, but we sure have a lot of shell casings,” Schultz said. “Taken together, the markers found in the samples offer intriguing evidence that North America had a major impact event about 12,900 years ago.”

Schultz admits that there is little decisive evidence about the actual details about the impact and its effects. Scientists suspect that a carbon-rich asteroid or comets were the culprits. The objects would have exploded over North America or slammed into it, or both, shattering and melting ice sheets, sparking extreme wildfires, and fueling hurricane-force winds – all of which could have contributed to changes in climate that led to the cooling of the Younger Dryas period.

“Our theory isn’t a slam dunk,” Schultz said. “We need to study a lot more sediments to get a lot more evidence. But what is sobering about this theory of ours is that this impact would be so recent. Not so long ago, something may have fallen from the sky and profoundly changed our climate and our culture.”

The U.S. Department of Energy and the National Science Foundation funded the work.
 
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Or maybe it did.

Case Closed? Comet Crash Killed Ice Age Beasts

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.

http://www.space.com/17676-comet-crash-ice-age.html
 
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Or maybe it didn't. Really ping pong this.

Study Rebuts Hypothesis That Comet Attacks Ended 9,000-Year-Old Clovis Culture

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

http://www.sciencedaily.com/releases/20 ... 095314.htm
 
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Not a near miss, but not that far back in time either.

Ice core data supports ancient space impact idea
By Simon Redfern, Reporter, BBC News

New data from Greenland ice cores suggest North America may have suffered a large cosmic impact about 12,900 years ago.
A layer of platinum is seen in ice of the same age as a known abrupt climate transition, US scientists report.
The climate flip has previously been linked to the demise of the North American "Clovis" people.

The data seem to back the idea that an impact tipped the climate into a colder phase, a point of current debate.
Rapid climate change occurred 12,900 years ago, and it is proposed that this is associated with the extinction of large mammals such as the mammoth, widespread wildfires, and rapid changes in atmospheric and ocean circulation.

All of these have previously been linked to a cosmic impact, but the theory has been hotly disputed due to lack of clear evidence.
New platinum measurements were made on ice cores that allow conditions 13,000 years ago to be determined at a time resolution of better than five years, report Michail Petaev and colleagues from Harvard University. Their results are published in the journal Proceedings of the National Academy of Sciences.

A 100-fold spike in platinum concentration occurs in ice that is around 12,890 years old, at just the same moment that rapid cooling of the climate is indicated from oxygen isotope measurements, at the start of a climatic period called the "Younger Dryas".
The Younger Dryas started and finished abruptly, and is one of a number of shorter periods of climate change that appear to have occurred since the last glacial maximum of 20,000 years ago.

Each end of the Younger Dryas period may have involved very rapid changes in temperature as the climate system reached a tipping point, with suggestions that dramatic changes in temperature occurred over as short as timescale as a decade or so.

The observations lend credence to earlier, disputed, reports that finds of microscopic grains of diamond and a mineral called lonsdaleite in lake sediments dated to the same time were identified with a possible meteorite impact.
Those measurements resemble the most recent observations of remnants of the Tunguska meteorite impact in Siberia, reported last month.

Sphere-shaped particles have also been identified at many localities in sediments dating to this event, most recently reported this month by a team led from Canada in the Journal of Geology. Such particles are characteristic of the rapidly heated and cooled splatter of material thrown up when meteorites hit Earth.

While the platinum data and the spherical particles add to evidence for an impact event, doubters have pointed out that, as yet, no impact site has been identified.

It has been suggested that debris thrown into the atmosphere in an impact tipped the Earth into global cooling at a rate as rapid as the global changes in climate in the reverse direction seen in the last century.

Such rapid climate change makes it difficult for ecologies and societies to adjust: It is the fluctuation that has been invoked as the cause of the extinction of massive mammals (megafauna) like the mammoth, and native cultures such as the Clovis people in North America.

The possible role of cosmic impacts in causing huge changes to life on Earth is receiving increased attention. The mass extinction 66 million years ago that wiped out the dinosaurs is generally believed to be linked to a space strike in southern Mexico's Yucatan Peninsula.
Recently, a group of scientists led by Eric Tohver at the University of Western Australia reported that the biggest extinction of all, which occurred 252.3 million years ago at the end of the Permian period, could be explained by an asteroid impact in Brazil.

Nasa is now focusing resources towards detection of future Earth-threatening asteroids, receiving over 400 responses to their recent request for ideas to feed into their Asteroid Grand Challenge, in which they hope to redirect a space rock and send humans to study it.

http://www.bbc.co.uk/news/science-environment-23536567
 
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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Ancient stone carvings confirm how comet struck Earth in 10,950BC, sparking the rise of civilisations
Sarah Knapton, Science Editor
21 April 2017 • 11:25am

Ancient stone carvings confirm that a comet struck the Earth around 11,000BC, a devastating event which wiped out woolly mammoths and sparked the rise of civilisations.

Experts at the University of Edinburgh analysed mysterious symbols carved onto stone pillars at Gobekli Tepe in southern Turkey, to find out if they could be linked to constellations.
The markings suggest that a swarm of comet fragments hit Earth at the exact same time that a mini-ice age struck, changing the entire course of human history.
Scientists have speculated for decades that a comet could be behind the sudden fall in temperature during a period known as the Younger Dryas. But recently the theory appeared to have been debunked by new dating of meteor craters in North America where the comet is thought to have struck.

However, when engineers studied animal carvings made on a pillar – known as the vulture stone – at Gobekli Tepe they discovered that the creatures were actually astronomical symbols which represented constellations and the comet.
The idea had been originally put forward by author Graham Hancock in his book Magicians of the Gods.

Using a computer programme to show where the constellations would have appeared above Turkey thousands of years ago, they were able to pinpoint the comet strike to 10,950BC, the exact time the Younger Dryas begins according to ice core data from Greenland.
The Younger Dryas is viewed as a crucial period for humanity, as it roughly coincides with the emergence of agriculture and the first Neolithic civilisations.

Before the strike, vast areas of wild wheat and barley had allowed nomadic hunters in the Middle East to establish permanent base camps. But the difficult climate conditions following the impact forced communities to come together and work out new ways of maintaining the crops, through watering and selective breeding. Thus farming began, allowing the rise of the first towns.

Edinburgh researchers said the carvings appear to have remained important to the people of Gobekli Tepe for millennia, suggesting that the event and cold climate that followed likely had a very serious impact.

etc...

http://www.telegraph.co.uk/science/...gs-confirm-comet-struck-earth-10950bc-wiping/

The astronomers Clube and Napier wrote two books on this ancient comet strike. I've posted about it a few times, somewhere on FTMB! eg,
http://forum.forteantimes.com/index.php?threads/comets.2782/page-3#post-968989
 
Two chemical engineers?
Looking at the paper doesn't build confidence either. It looks loke they started with their conclusion and worked at it until they made things fit, cranes are more present than snakes, but no mention is made of them, and most of their conclusions of the symbols are their own invention.
To say nothing of them using a much more recent set of constellations and forcing tgem onto a much more ancient structure.
 
Also they are off by 5 to 6 thousand years on their extinction idea. Did they even do basic research before coming up with this BS?
 
Ancient stone carvings confirm how comet struck Earth in 10,950BC, sparking the rise of civilisations
Sarah Knapton, Science Editor
21 April 2017 • 11:25am

Ancient stone carvings confirm that a comet struck the Earth around 11,000BC, a devastating event which wiped out woolly mammoths and sparked the rise of civilisations.

Experts at the University of Edinburgh analysed mysterious symbols carved onto stone pillars at Gobekli Tepe in southern Turkey, to find out if they could be linked to constellations.
The markings suggest that a swarm of comet fragments hit Earth at the exact same time that a mini-ice age struck, changing the entire course of human history.
Scientists have speculated for decades that a comet could be behind the sudden fall in temperature during a period known as the Younger Dryas. But recently the theory appeared to have been debunked by new dating of meteor craters in North America where the comet is thought to have struck.

However, when engineers studied animal carvings made on a pillar – known as the vulture stone – at Gobekli Tepe they discovered that the creatures were actually astronomical symbols which represented constellations and the comet.
The idea had been originally put forward by author Graham Hancock in his book Magicians of the Gods.

Using a computer programme to show where the constellations would have appeared above Turkey thousands of years ago, they were able to pinpoint the comet strike to 10,950BC, the exact time the Younger Dryas begins according to ice core data from Greenland.
The Younger Dryas is viewed as a crucial period for humanity, as it roughly coincides with the emergence of agriculture and the first Neolithic civilisations.

Before the strike, vast areas of wild wheat and barley had allowed nomadic hunters in the Middle East to establish permanent base camps. But the difficult climate conditions following the impact forced communities to come together and work out new ways of maintaining the crops, through watering and selective breeding. Thus farming began, allowing the rise of the first towns.

Edinburgh researchers said the carvings appear to have remained important to the people of Gobekli Tepe for millennia, suggesting that the event and cold climate that followed likely had a very serious impact.

etc...

http://www.telegraph.co.uk/science/...gs-confirm-comet-struck-earth-10950bc-wiping/

The astronomers Clube and Napier wrote two books on this ancient comet strike. I've posted about it a few times, somewhere on FTMB! eg,
http://forum.forteantimes.com/index.php?threads/comets.2782/page-3#post-968989

Graham Hancock right again ... imagine how much history was lost back then what with comets hitting and an ice age all going on at once ... followed of course in quick succession by the ice caps melting again as the atmosphere cleared from all the airborne dust.
 
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
 
Graham Hancock right again ... imagine how much history was lost back then what with comets hitting and an ice age all going on at once ... followed of course in quick succession by the ice caps melting again as the atmosphere cleared from all the airborne dust.

The problem with Graham Hancock is that he can be to presumptuous and not entirely scientific.
 
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
 
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
 
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
 
Researchers find evidence of a cosmic impact that caused destruction of one of the world's earliest human settlements

Source: phys.org
Date: 7 March, 2020

Before the Taqba Dam impounded the Euphrates River in northern Syria in the 1970s, an archaeological site named Abu Hureyra bore witness to the moment ancient nomadic people first settled down and started cultivating crops. A large mound marks the settlement, which now lies under Lake Assad.

But before the lake formed, archaeologists were able to carefully extract and describe much material, including parts of houses, food and tools—an abundance of evidence that allowed them to identify the transition to agriculture nearly 12,800 years ago. It was one of the most significant events in our Earth's cultural and environmental history.

Abu Hureyra, it turns out, has another story to tell. Found among the cereals and grains and splashed on early building material and animal bones was meltglass, some features of which suggest it was formed at extremely high temperatures—far higher than what humans could achieve at the time—or that could be attributed to fire, lighting or volcanism.

https://m.phys.org/news/2020-03-evidence-cosmic-impact-destruction-world.html
 
Before the Taqba Dam impounded the Euphrates River in northern Syria in the 1970s, an archaeological site named Abu Hureyra bore witness to the moment ancient nomadic people first settled down and started cultivating crops. A large mound marks the settlement, which now lies under Lake Assad.

18-researchersf.jpg


But before the lake formed, archaeologists were able to carefully extract and describe much material, including parts of houses, food and tools—an abundance of evidence that allowed them to identify the transition to agriculture nearly 12,800 years ago. It was one of the most significant events in our Earth's cultural and environmental history.

Abu Hureyra, it turns out, has another story to tell. Found among the cereals and grains and splashed on early building material and animal bones was meltglass, some features of which suggest it was formed at extremely high temperatures—far higher than what humans could achieve at the time—or that could be attributed to fire, lighting or volcanism.

"To help with perspective, such high temperatures would completely melt an automobile in less than a minute," said James Kennett, a UC Santa Barbara emeritus professor of geology. Such intensity, he added, could only have resulted from an extremely violent, high-energy, high-velocity phenomenon, something on the order of a cosmic impact.

Based on materials collected before the site was flooded, Kennett and his colleagues contend Abu Hureyra is the first site to document the direct effects of a fragmented comet on a human settlement. These fragments are all part of the same comet that likely slammed into Earth and exploded in the atmosphere at the end of the Pleistocene epoch, according to Kennett. This impact contributed to the extinction of most large animals, including mammoths, and American horses and camels; the disappearance of the North American Clovis culture; and to the abrupt onset of the end-glacial Younger Dryas cooling episode.

The team's findings are highlighted in a paper published in the Nature journal Scientific Reports.

https://phys.org/news/2020-03-evidence-cosmic-impact-destruction-world.html

maximus otter
 
The published paper on the Abu Hureyra discoveries and analyses is now available at:

https://www.nature.com/articles/s41598-020-60867-w
Abstract
At Abu Hureyra (AH), Syria, the 12,800-year-old Younger Dryas boundary layer (YDB) contains peak abundances in meltglass, nanodiamonds, microspherules, and charcoal. AH meltglass comprises 1.6 wt.% of bulk sediment, and crossed polarizers indicate that the meltglass is isotropic. High YDB concentrations of iridium, platinum, nickel, and cobalt suggest mixing of melted local sediment with small quantities of meteoritic material. Approximately 40% of AH glass display carbon-infused, siliceous plant imprints that laboratory experiments show formed at a minimum of 1200°–1300 °C; however, reflectance-inferred temperatures for the encapsulated carbon were lower by up to 1000 °C. Alternately, melted grains of quartz, chromferide, and magnetite in AH glass suggest exposure to minimum temperatures of 1720 °C ranging to >2200 °C. This argues against formation of AH meltglass in thatched hut fires at 1100°–1200 °C, and low values of remanent magnetism indicate the meltglass was not created by lightning. Low meltglass water content (0.02–0.05% H2O) is consistent with a formation process similar to that of tektites and inconsistent with volcanism and anthropogenesis. The wide range of evidence supports the hypothesis that a cosmic event occurred at Abu Hureyra ~12,800 years ago, coeval with impacts that deposited high-temperature meltglass, melted microspherules, and/or platinum at other YDB sites on four continents.
 
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