[meteorite-list] Extraterrestrial Impact Likely Source of Sudden Ice Age Extinctions

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 25 Sep 2007 16:53:53 -0700 (PDT)
Message-ID: <200709252353.QAA09891_at_zagami.jpl.nasa.gov>

http://www.brown.edu/Administration/News_Bureau/2007-08/07-040.html

September 24, 2007
Contact: Wendy Lawton <mailto:Media_Relations at brown.edu>
(401) 863-2476

Extraterrestrial Impact Likely Source of Sudden Ice Age Extinctions

What killed the wooly mammoths? An international team of scientists,
including Peter Schultz of Brown University, suggests that a comet or
meteorite exploded over the planet roughly 12,900 years ago, causing the
abrupt climate changes that led to the extinction of the wooly mammoth
and other giant prehistoric beasts. Their theory is published in the
Proceedings of the National Academy of Sciences.

------------------------------------------------------------------------

PROVIDENCE, R.I. [Brown University] - At the end of the Pleistocene era,
wooly mammoths roamed North America along with a cast of fantastic
creatures - giant sloths, saber-toothed cats, camels, lions, tapirs and
the incredible teratorn, a condor with a 16-foot wingspan.

About 12,900 years ago, these megafauna disappeared from the fossil
record, as did evidence of human remains. The cause of the mass
extinction and the human migration is a mystery. Now a team of
scientists, including Brown University planetary geologist Peter
Schultz, provides evidence that an asteroid impact likely caused the
sudden climate changes that killed off the mammoths and other majestic
beasts of prehistory.

In the Proceedings of the National Academy of Sciences, the
international team lays out its theory that the mass extinctions in
North America were caused by one or more extraterrestrial objects -
comets or meteorites - that exploded over the Earth or slammed into it,
triggering catastrophic climate change.

The scientists believe that evidence for these extraterrestrial impacts
is hidden in a dark layer of dirt sometimes called a black mat. Found in
more than 50 sites around North America, this puzzling slice of
geological history is a mere three centimeters deep and filled with
carbon, which lends the layer its dark color. This black mat has been
found in archaeological digs in Canada and California, Arizona and South
Carolina - even in a research site in Belgium.

The formation of this layer dates back 12,900 years and coincides with
the abrupt cooling of the Younger Dryas period, sometimes called the
"Big Freeze." This coincidence intrigued the researchers, led by Richard
Firestone of Lawrence Berkeley National Laboratory, who thought that the
black mat might be related to the mass extinctions.

So the researchers studied black mat sediment samples from 10
archaeological sites dating back to the Clovis people, the first human
inhabitants of the New World. Researchers conducted geochemical analysis
of the samples to determine their makeup and also ran carbon dating
tests to determine the age of the samples.

Directly beneath the black mat, researchers found high concentrations of
magnetic grains containing iridium, charcoal, soot, carbon spherules,
glass-like carbon containing nanodiamonds and fullerenes packed with
extraterrestrial helium - all of which are evidence for an
extraterrestrial impact and the raging wildfires that might have followed.

Schultz, professor of geological sciences at Brown and an impact
specialist, said the most provocative evidence for an extraterrestrial
impact was the discovery of nanodiamonds, microscopic bits of diamond
formed only from the kind of intense pressure you'd get from a comet or
meteorite slamming into the Earth.

"We don't have a smoking gun for our theory, but we sure have a lot of
shell casings," Schultz said. "Taken together, the markers found in the
samples offer intriguing evidence that North America had a major impact
event about 12,900 years ago."

Schultz admits that there is little decisive evidence about the actual
details about the impact and its effects. Scientists suspect that a
carbon-rich asteroid or comets were the culprits. The objects would have
exploded over North America or slammed into it, or both, shattering and
melting ice sheets, sparking extreme wildfires, and fueling
hurricane-force winds - all of which could have contributed to changes
in climate that led to the cooling of the Younger Dryas period.

"Our theory isn't a slam dunk," Schultz said. "We need to study a lot
more sediments to get a lot more evidence. But what is sobering about
this theory of ours is that this impact would be so recent. Not so long
ago, something may have fallen from the sky and profoundly changed our
climate and our culture."

The U.S. Department of Energy and the National Science Foundation funded
the work.

Editors: Brown University has a fiber link television studio available
for domestic and international live and taped interviews and maintains
an ISDN line for radio interviews. For more information, call the Office
of Media Relations at (401) 863-2476.

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Received on Tue 25 Sep 2007 07:53:53 PM PDT