* Astronomy

Blobrana · L

RE: Younger Dryas Impact

Blobrana · L

Did a Comet Cause a North American Die-Off around 13,000 Years Ago?
Researchers have found shock-synthesized hexagonal diamonds on one of California's Channel Islands, which they say is the strongest evidence yet that a comet exploded in the atmosphere above North America, causing widespread extinctions there around 12,900 years ago. Skeptics, however, say the debate is far from over.

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Blobrana · L

Its just a theory, but its an interesting one.
David Ollen may have found evidence of a massive impact crater just south of Kitscoty, but it doesnt look anything like what you might expect.
Instead of a huge hole in the ground, its a circular plateau about 30 kilometres in diameter, with an inner circle about12 kilometres in diameter.
If it is evidence of an impact, it may have happened during the last ice age, when the area around Lloydminster was under a huge mass of ice.

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Beware Earth-shattering headlines
Few editors can resist a disaster story, even one that happened in the distant past. So it is little wonder that the press jumped all over claims by a team of 25 researchers in 2007 that a mysterious impact on the North American ice sheet 12,900 years ago wiped out the continent's Pleistocene megafauna and the Clovis culture of the early settlers, and wreaked havoc on the global climate.

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Title: Wildfire responses to abrupt climate change in North America
Authors: J. R. Marlona,1, P. J. Bartleina, M. K. Walsha, S. P. Harrisonb, K. J. Brownc, M. E. Edwardse, P. E. Higuerag, M. J. Powerh, R. S. Andersoni, C. Brilesg, A. Brunelleh, C. Carcailletj, M. Danielsk, F. S. Hul, M. Lavoiem, C. Longn, T. Minckleyo, P. J. H. Richardp, A. C. Scottq, D. S. Shaferr, W. Tinners, C. E. Umbanhowar, Jr. and C. Whitlockg

It is widely accepted, based on data from the last few decades and on model simulations, that anthropogenic climate change will cause increased fire activity. However, less attention has been paid to the relationship between abrupt climate changes and heightened fire activity in the paleorecord. We use 35 charcoal and pollen records to assess how fire regimes in North America changed during the last glacial-interglacial transition (15 to 10 ka), a time of large and rapid climate changes. We also test the hypothesis that a comet impact initiated continental-scale wildfires at 12.9 ka; the data do not support this idea, nor are continent-wide fires indicated at any time during deglaciation. There are, however, clear links between large climate changes and fire activity. Biomass burning gradually increased from the glacial period to the beginning of the Younger Dryas. Although there are changes in biomass burning during the Younger Dryas, there is no systematic trend. There is a further increase in biomass burning after the Younger Dryas. Intervals of rapid climate change at 13.9, 13.2, and 11.7 ka are marked by large increases in fire activity. The timing of changes in fire is not coincident with changes in human population density or the timing of the extinction of the megafauna. Although these factors could have contributed to fire-regime changes at individual sites or at specific times, the charcoal data indicate an important role for climate, and particularly rapid climate change, in determining broad-scale levels of fire activity.

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Comet impact theory disproved
New data, published today, disproves the recent theory that a large comet exploded over North America 12,900 years ago, causing a shock wave that travelled 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.

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Blobrana · L

Nano-diamonds (or nano-sized diamonds) are thought to have been created out of the carbon by exposure to shock. Cubic diamonds - the kind you buy from the jewellery store - form under high temperatures and pressures, temperatures that surely would have killed everything and everybody; nano-diamonds formed under a lesser shock.

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Nanodiamonds that have been discovered in ancient sediment provide new support for a divisive theory that a giant space rock wiped out humans and animals thousands of years ago.
The 'Clovis' culture, which thrived in North America on a diet of mammoth, bison and horse, disappeared suddenly 13,000 years ago. While several theories have been offered to explain this perplexing vanishing act, some two dozen scientists controversially proposed in May 2007 that these people and the beasts they hunted were killed by space rocks that exploded on or above North America, changing the climate. With the discovery of fresh evidence, reported in Science, the debate looks set to continue.

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Diamonds show comet struck North America
The impact caused an ice age that killed some mammal species and many humans 12,900 years ago, researchers report. They say the discovery of tiny heat-formed diamonds is proof of the catastrophe.

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Abundant tiny particles of diamond dust exist in sediments dating to 12,900 years ago at six North American sites, adding strong evidence for Earths impact with a rare swarm of carbon-and-water-rich comets or carbonaceous chondrites, reports a nine-member scientific team.
These nanodiamonds, which are produced under high-temperature, high-pressure conditions created by cosmic impacts and have been found in meteorites, are concentrated in similarly aged sediments at Murray Springs, Ariz., Bull Creek, Okla., Gainey, Mich., and Topper, S.C., as well as Lake Hind, Manitoba, and Chobot, Alberta, in Canada. Nanodiamonds can be produced on Earth, but only through high-explosive detonations or chemical vaporisation.
Last year a 26-member team from 16 institutions proposed that a cosmic impact event, possibly by multiple airbursts of comets, set off a 1,300-year-long cold spell known as the Younger Dryas, fragmented the prehistoric Clovis culture and led to the extinction of a large range of animals, including mammoths, across North America. The team's paper was published in the Oct. 9, 2007, issue of the Proceedings of the National Academy of Sciences.

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