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Extraterrestrial
Impact Likely Source Of Sudden Ice Age Extinctions Date: September 25, 2007 Source: Brown University Summary: What killed the woolly mammoths? Scientists
now 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 woolly mammoth and other giant prehistoric beasts. Share:
FULL STORY
A colorized scanning
electron microscope image of a glassy carbon sphere that contains evidence of
extraterrestrial impact. The sphere measures about .012 inches in width. Credit: SEM imaging
by Jim Wittke At the end of the
Pleistocene era, woolly 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. Story Source: Materials provided
by Brown
University. Note: Content may be edited for style and
length. Cite This Page: ·
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Chicago Brown University. "Extraterrestrial Impact Likely Source Of Sudden Ice Age Extinctions." ScienceDaily. ScienceDaily,
25 September 2007.
<www.sciencedaily.com/releases/2007/09/070924172959.htm>. |
