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Scientists Round up New Suspect In Case of Vanishing Mammoths
(From the November/December 2007 issue of StarDate magazine)
When scientists look for the cause of mass extinctions, comets and asteroids top the list of "usual suspects." An example is the demise of mammoths, the big, wooly creatures with enormous tusks featured in "Ice Age" and caveman movies.
In May, a team of scientists led by Allen West of Geoscience Consulting in Dewey, Arizona, suggested that a comet or asteroid exploded over Canada 12,900 years ago, triggering an environmental catastrophe that killed the mammoths and decimated the prehistoric Clovis culture.
The scientists examined layers of sediment at 26 locations across North America. A charred layer deposited almost 13,000 years ago contains small, glasslike beads of carbon, which could have been created when a blast wave hit the surface, melting material and throwing it high into the atmosphere; carbon spherules created under high pressure; and magnetic grains that are rich in iridium, an element that is rare on Earth but more common in comets and asteroids.
The layers beneath this sooty deposit contain mammoth fossils and the artifacts of the Clovis culture, while layers above it are bereft of these items, the scientists reported.
They suggested that the explosion melted large parts of the Canadian ice sheet, pumping freshwater into the North Atlantic. It also triggered widespread fires that filled the air with smoke and debris, cooling the climate by almost 20 degrees Fahrenheit.
Not all scientists agree with the interpretation, though. Some say the chemistry doesn't match across the entire continent, for example. Others had already proposed that an exploding star could have killed the mammoths.
So while some evidence points to a comet or asteroid as the culprit, the case of the disappearing mammoths is not yet ready to go to the jury. — Damond Benningfield
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