[lbo-talk] Apropos climate change and the megafauna mass extinctions

Michael Pollak mpollak at panix.com
Thu Jan 1 22:46:29 PST 2009


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.

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Full at: http://www.nytimes.com/2009/01/02/science/02impact.html

Michael



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