posted 05-14-2007 01:44 PM            

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A comet or some other extraterrestrial object appears to have slammed into northern Canada 12,900 years ago and triggered an abrupt and catastrophic climate change that wiped out the mammoths and many other prehistoric creatures, according to a team of U.S. scientists.
<snip>
Geophysicist Jerry Mitrovica at the University of Toronto is also skeptical. "I'll wait to see the published papers," <my emphasis>

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Did comet start deadly cold snap?

Edit - My url became unwound.

posted 05-14-2007 06:02 PM            

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Originally posted by KGB:
So we don't see a crater because the comet hit kilometers-thick ice? That doesn't sound implausible, but I'm guessing there would still be shatter cones and coesite formation from the shock wave propagating through the ice into rock. If they find recent shatter cones somewhere where there isn't a crater, I'll be convinced.

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I tend to agee. Kilometers of ice doesn't really mean very much to an object travelling 30 kilometers a secon. IIRC an impactor vaporizes about 10 times its diamater worth of rock and liquifies about 20 times its diameter.

You also have the interesting problem of faunal selectivity. Most animals that went extinct at the close of the Pleistocene were megafauna: mammals with a body weight of greater than 40 kilograms. Squirrels, rabbits, mice, etc. all survive; it think there's one species of skunk that departs but that's about it. (There are a number of extinct Pleistocene birds, but they all seems to be carrion feeders. OTOH most of the bird faunal record comes from the La Brea tar pits, where carrion feeders would be favored).

posted 05-15-2007 10:20 AM            

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Originally posted by setnahkt:
You would also have to explain why the hypothetical comet killed of around 75% of the North and South American megafauna, but only about 15% of the Old World megafauna (15% is about the nuber that would normally go extinct in an equivalent time.)

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That's easy. Peoples in Asia saw this big fireball god thing fly across the sky towards the east. They crossed the Bearing land bridge in an effort to find what the gods wanted them to see. They entered a promised land that was unpeopled and full of large game. As they prospered, many large mammals were hunted to the point of extinction.