* Astronomy

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Younger Dryas

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RE: Younger Dryas Impact

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Evidence found for planet-cooling asteroid

The dust refuses to settle on a debate about whether asteroid impacts caused one of Earth's most famous cold snaps 12,900 years ago.
The latest evidence in the contentious discussion comes in the form of pieces of bedrock from Quebec, Canada, that seem to have been blasted out as far as Pennsylvania. "I'd say there's evidence of an impact happening, for sure," says Mukul Sharma, an isotope geochemist at Dartmouth College in Hanover, New Hampshire, and co-author of a study published this week in Proceedings of the National Academy of Sciences.
Between 11,600 and 12,900 years ago, the planet's climate changed rapidly: in northern climes such as Greenland, temperatures dropped by several degrees in less than a century. No one knows what caused the deep freeze, known as the Younger Dryas.
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Ice core data supports ancient space impact idea

New data from Greenland ice cores suggest North America may have suffered a large cosmic impact about 12,890 years ago.
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Scientists Challenge Theory of Massive Comet or Meteorite Hit to Wipe out Mammoth

A 16-member research team from the United States, Britain and Belgium has challenged the hotly disputed theory that a massive comet or meteorite struck a glacier-encased Hudson Bay about 13,000 years ago.
The theory suggested that the impact was so strong that it wiped out the mammoths and other Ice Age megafauna. Moreover, it destroyed the first major wave of human migration in the new world.
The research team published their major study in February and said that there us a lack of clear evidence to prove that a four-kilometer-wide comet exploded across the Laurentide Ice Sheet that covered ancient Canada.
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The Mammoth's Lament: UC Research Shows How Cosmic Impact Sparked Devastating Climate Change

Herds of wooly mammoths once shook the earth beneath their feet, sending humans scurrying across the landscape of prehistoric Ohio. But then something much larger shook the Earth itself, and at that point these mega mammals' days were numbered.
Something - global-scale combustion caused by a comet scraping our planet's atmosphere or a meteorite slamming into its surface - scorched the air, melted bedrock and altered the course of Earth's history. Exactly what it was is unclear, but this event jump-started what Kenneth Tankersley, an assistant professor of anthropology and geology at the University of Cincinnati, calls the last gasp of the last ice age.
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Prehistoric Americans not wiped out by comet - researchers

Comet explosions did not end the prehistoric human culture, known as Clovis, in North America 13,000 years ago, according to research published in the journal, Geophysical Monograph Series.
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Title: Independent evaluation of conflicting microspherule results from different investigations of the Younger Dryas impact hypothesis
Authors: Malcolm A. LeCompte, Albert C. Goodyear, Mark N. Demitroff, Dale Batchelor, Edward K. Vogel, Charles Mooney, Barrett N. Rock, and Alfred W. Seidel

Firestone et al. sampled sedimentary sequences at many sites across North America, Europe, and Asia [Firestone RB, et al. (2007) Proc Natl Acad Sci USA 106:16016-16021]. In sediments dated to the Younger Dryas onset or Boundary (YDB) approximately 12,900 calendar years ago, Firestone et al. reported discovery of markers, including nanodiamonds, aciniform soot, high-temperature melt-glass, and magnetic microspherules attributed to cosmic impacts/airbursts. The microspherules were explained as either cosmic material ablation or terrestrial ejecta from a hypothesised North American impact that initiated the abrupt Younger Dryas cooling, contributed to megafaunal extinctions, and triggered human cultural shifts and population declines. A number of independent groups have confirmed the presence of YDB spherules, but two have not. One of them [Surovell TA, et al. (2009) Proc Natl Acad Sci USA 104:18155-18158] collected and analysed samples from seven YDB sites, purportedly using the same protocol as Firestone et al., but did not find a single spherule in YDB sediments at two previously reported sites. To examine this discrepancy, we conducted an independent blind investigation of two sites common to both studies, and a third site investigated only by Surovell et al. We found abundant YDB microspherules at all three widely separated sites consistent with the results of Firestone et al. and conclude that the analytical protocol employed by Surovell et al. deviated significantly from that of Firestone et al. Morphological and geochemical analyses of YDB spherules suggest they are not cosmic, volcanic, authigenic, or anthropogenic in origin. Instead, they appear to have formed from abrupt melting and quenching of terrestrial materials.

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Ed ~ Proof? No. And, even if the microspherules turn out to be of impact origin; we know that small impacts occur quite frequently (eg Tunguska) and can seed localised areas with microspherules.

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New evidence that extraterrestrial impact killed off the mammoths

Melted glass buried deep within the Earth at sites around the world confirms the theory that a comet or meteor struck the planet nearly 13,000 years ago, triggering the Younger Dryas Ice Age, killing off the mammoths and other megafauna in North America, and perhaps even causing the disappearance of the Clovis culture of early Native Americans. The cause of the Younger Dryas cooling period has been very controversial. Some researchers have proposed an extraterrestrial impact and have produced evidence of the event, but others claim that the results have not been replicated. The new findings, reported this week in the Proceedings of the National Academy of Sciences, appear to provide that needed replication.
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Younger Dryas Impact