>From CBC:
http://www.cbc.ca/technology/story/2007/09/25/carbon-clovis.html
Extra-terrestrial impact did in mammoths: scientists
Last Updated: Tuesday, September 25, 2007 | 1:10 PM ET
CBC News
A thin layer of carbon and debris laid down 12,900 years ago supports the
theory that the extinction of mammoths and other large mammals was caused by an
"extra-terrestrial" event, researchers reported Tuesday.
The cause of the sudden disappearance of 35 kinds of mammal â including
mastodons, ground sloths, horses and camels â from North America is a matter
of continuing controversy, with human overhunting being the main alternative
theory to sudden cooling.
[Photograph of a Mammoth]
The skeleton of a 15,000-year-old mammoth. The giant animals might have
become extinct after an object from space hit the Earth's atmosphere, changing
the climate, researchers suggested. The skeleton of a 15,000-year-old mammoth.
The giant animals might have become extinct after an object from space hit the
Earth's atmosphere, changing the climate, researchers suggested.
(Francois Mori/Associated Press)
The 26 authors of Tuesday's paper, published in the Proceedings of the National
Academy of Sciences, come down on the side of sudden cooling, based on studies
of 10 North American sites from the Clovis Period, an era when humans hunted
mastodons. It ended suddenly about the same time the carbon appeared.
They suggest that "multiple ET airbursts along with surface impacts" â
possibly by an asteroid, comet or meteorite â and the massive wildfires that
followed laid down a three-centimetre carbon-rich "black layer" with elements
of soot, charcoal and glass-like carbon over the Clovis sites.
The base of the layer coincides with the beginning of the Younger Dryas cooling
period, a 1,000-year ice age that began about the same time that Clovis culture
ended.
The researchers said there were Clovis tools and "megafauna" bones under the
layer, but none in or on top of it.
"We don't have a smoking gun for our theory, but we sure have a lot of shell
casings," Brown University planetary geologist Peter Schultz said in a
statement. "Taken together, the markers found in the samples offer intriguing
evidence that North America had a major impact event about 12,900 years ago."
He was one of the researchers, led by Richard Firestone of Lawrence Berkeley
National Laboratory in Berkeley, Calif.
The Clovis culture had spears capable of piercing a mammoth and might have
lived by following herds of the giant animals. The Clovis population declined
as the animals disappeared, to be replaced by Folsom culture, which arose as
the continent warmed after the Younger Dryas period.
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