* Astronomy

New scientific findings suggest that a large comet may have exploded over North America 12,900 years ago, explaining riddles that scientists have wrestled with for decades, including an abrupt cooling of much of the planet and the extinction of large mammals.
The discovery was made by scientists from the University of California at Santa Barbara and their colleagues. James Kennett, a paleoceanographer at the university, said that the discovery may explain some of the highly debated geologic controversies of recent decades.
The period in question is called the Younger Dryas, an interval of abrupt cooling that lasted for about 1,000 years and occurred at the beginning of an inter-glacial warm period. Evidence for the temperature change is recorded in marine sediments and ice cores.

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Some 12,900 years ago disaster struck the North American continent. The Earth's climate, which had been getting steadily warmer at the tail end of the retreating Ice Age, suddenly dropped catastrophically. The megafauna, such as camels and mammoth died out. And the first people to populate the American landscape saw their numbers drop by an estimated 75%. A number of explanations have been offered for why this happened. One of the latest is that cataclysmic event thought to have caused several other upheavals in the Earth's history, an impact from outer space.

While they have been unable to point to any central impact crater, this could be explained by the bolide disintegrating in the air, and the principal strike zone being covered by glaciation. They also point to four large trenches below the present Great Lakes as possible testaments to the impact. The so called Carolina bays, located in line with the lakes, as well as thousands of smaller features along the Atlantic coast, might also have been a result of the impact. But some geologists protest that there are other, and far more plausible explanations for these features.
The researchers think they have found chemical traces of the impact in geological strata on 25 different locations, 9 of which are Clovis sites. They also claim to have found traces as far away as Belgium. In a thin layer of soil, they have found minute spheres of glass and carbon (nano-diamonds), which are related to meteor impacts. They've also found high levels of Iridium, and other materials more common in space debris than here on Earth.
In addition they've found a layer of ash, across the whole continent, as if a gigantic fires had raged across the landscape. The ash is laid down just below the Younger Dryas, according to their studies. Did the Clovis people, and the giant mammals perish in horrific fires, followed by darkness and a long cold period? All we know for sure is that the number of arrowheads, and probably the number of people, fall by 75% following this period. The America that emerged from the catastrophe, would be totally different from the one that had once been.

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Mammoth-Killer Impact Gets Mixed Reception From Earth Scientists
A headline-grabbing proposal that an exploding comet wreaked havoc on man and beast 13,000 years ago got its first full scientific airing at a meeting here last week. But geoscientists are not dashing off to rewrite the textbooks yet.

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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.
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.

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