New Scientific Paper on Younger Dryas Impact Event

From the MYTimes article...

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.

And 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 one 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 Science paper say it was meteors.

Link: NYTimes Article (New Evidence of Meteor Bombardment, Kenneth Chang, January 1, 2009)

Link: Younger Dryas impact event (Wikipedia)

Link: Science Article (Nanodiamonds in the Younger Dryas Boundary Sediment Layer, D. J. Kennett, et al, Science 2 January 2009: Vol. 323. no. 5910, p. 94).