Friday, April 2, 2010

Comet fragments 'strafed' Canada

Massive comet striking Canada may have triggered prehistoric extinctions
Vancouver Sun: A British astronomer has published new evidence that North America was strafed by thousands of fragments from a massive comet about 12,900 years ago, a theory he says is the best explanation yet for why the planet was plunged into a 1,000-year cooling period and dozens of Ice Age mammals went extinct at that time.

Many scientists have argued in recent years that a meteorite impact centred around Hudson Bay smashed the retreating Laurentide glacier and triggered a distinctly frigid period of global climate change known as the Younger Dryas. But that hypothesis has been controversial, argues Cardiff University astronomer Bill Napier, because even though an extraterrestrial event is likely to have occurred around 12,000 BC, conclusive proof of 'a large single collision' has been lacking.

The answer, he contends... is a scenario in which the Earth is rocked by an hour-long series of comet blasts across a wide swath of Canada and the United States, sparking continent-wide forest fires and other fallout that doomed many large species, disrupted early settlement of the Americas and launched a new mini-ice age...

One of the clues... is a 'nanodiamond'-rich Canadian meteorite that crashed into frozen Tagish Lake along the Yukon-BC border in January 2000. The impact left a precious scattering of uncontaminated rock believed to be more than 4.5 billion years old. Researchers have also documented a thin layer of microscopic 'shocked' diamonds at various North American sites consistent with some kind of extraterrestrial impact about 12,900 years ago...

'A large comet has been disintegrating in the near-Earth environment for the past 20,000 to 30,000 years, and running into thousands of fragments from this comet is a much more likely event than a single large collision,' Napier states in the summary. 'It gives a convincing match to the major geophysical features at this boundary.' He argues that the culprit comet still exists today as part of an assemblage of meteor streams and asteroids called the Taurid Complex.
Image source here.