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Ice age impact? More evidence vanishes.

It sounded good at the time. But the theory that a comet hit North America 12,900 years ago, causing widespread fires and climate cooling that killed off" the mammoths, saber-toothed cats, and other great mammals (S&T: September 2009 cover story), continues to crumble.

Proponents of the theory have offered carbonaceous spherules and "nanodiamonds" formed by intense heat as evidence of an impact. But a new study finds that these are merely fossilized bits of fungus, charcoal, and other organic matter. Moreover, they date from times spanning thousands of years before and after the start of the Younger Dryas cool period, not from a timespan of less than a century as originally reported--ruling out an impact origin. "There just isn't the evidence to support it," says Andrew C. Scott (University of London, England), who led the study. His group's findings will appear in Geophysical Research Letters.

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Title Annotation:News Notes
Publication:Sky & Telescope
Article Type:Brief article
Geographic Code:4EUUK
Date:Sep 1, 2010
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