http://www.nytimes.com/2009/01/02/science/02impact.html
The New York Times
January 2, 2009
New Evidence of Meteor Bombardment
By KENNETH CHANG
At least once in Earth's history, global warming ended quickly, and
scientists have long wondered why.
Now researchers are reporting that the abrupt cooling -- which took
place about 12,900 years ago, just as the planet was emerging from an
ice age -- may have been caused by one or more meteors that slammed
into North America.
That could explain the extinction of mammoths, saber-tooth tigers and
maybe even the first human inhabitants of the Americas, the scientists
report in Friday's issue of the journal Science.
The hypothesis has been regarded skeptically, but its advocates now
report perhaps more convincing residue of impact: a thin layer of
microscopic diamonds found in rocks across America and in Europe.
"We're up over 30 sites, as far west as offshore California, as far
east as Germany," said Allen West, a retired geology consultant who is
one of the scientists working on the research.
The meteors would have been smaller than the six-mile-wide meteor that
struck the Yucatán peninsula 65 million years ago and led to the mass
extinctions of the dinosaurs. The killing effects of the hypothesized
bombardment 12,900 years ago would have been more subtle.
Climatologists believe that the direct cause of the 1,300-year cold
spell, known as the Younger Dryas, was a sudden rush of fresh water
from a giant lake in central Canada to the North Atlantic.
Usually a surface current of warm water flows northward in the Atlantic
toward Greenland and Europe, then cools and sinks, returning south in
the deep ocean. But the fresh water, which is less dense, blocked the
sinking of the cold, salty water in the North Atlantic, disrupting the
currents.
That sudden change in plumbing has long been known, but what caused it
has never been satisfactorily explained.
The authors of the paper in Science say it was meteors.
<end excerpt>
Full at: http://www.nytimes.com/2009/01/02/science/02impact.html
Michael