[FPSPACE] new evidence of meteorite strikes on North America 13, 000 ybp..from the New York Times

[Peter Pesavento]

EP Grondine should enjoy this..it seems they are finding stuff all over the
place

 

http://www.nytimes.com/2009/01/02/science/02impact.html?hp=
<http://www.nytimes.com/2009/01/02/science/02impact.html?hp=&pagewanted=prin
t> &pagewanted=print

 

January 2, 2009


New Evidence of Meteor Bombardment 


By KENNETH CHANG
<http://topics.nytimes.com/top/reference/timestopics/people/c/kenneth_chang/
index.html?inline=nyt-per> 

At least once in Earth
<http://topics.nytimes.com/top/news/science/topics/earth_planet/index.html?i
nline=nyt-classifier> ’s history, global warming
<http://topics.nytimes.com/top/news/science/topics/globalwarming/index.html?
inline=nyt-classifier>  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.

At each site the scientists looked at, the diamond layer in the rocks
correlates to the date of the hypothesized impact. Within the layer, the
scientists report finding a multitude of diamond particles, all encased
within carbon spheres. “We’ve yet to find a single diamond above it,” Dr.
West said. “We’ve yet to find a single diamond below it.” 

Perhaps more telling, the scientists reported last month at a meeting of the
American Geophysical Union in San Francisco, the carbon atoms inside some of
the diamonds are lined up in a hexagonal crystal pattern instead of the
usual cubic structure. The hexagonal diamonds, formed by extraordinary heat
and pressure, have been found only at impact craters and within meteorites
and cannot be formed in forest fires or volcanic eruptions, Dr. West said.

Last year the scientists presented other evidence of an impact, including
elevated levels of the element iridium.

At least some skeptics are not convinced. “The whole thing still does not
make sense, and there are lots of contradictions,” said Christian Koeberl, a
professor of geological sciences at the University of Vienna in Austria.

His chief reservation: there’s no crater. “A body of this size does not just
blow up without a trace in the atmosphere,” Dr. Koeberl said. “Physics won’t
have it.”

Proponents have suggested that the meteor hit an ice sheet a couple of miles
thick or that there were a series of smaller objects that exploded in the
air. But Dr. Koeberl said something hitting an ice sheet would still
generate a hole in the ground underneath, and he questioned whether smaller
impacts or air explosions would produce the shock waves needed to make
diamonds.

An impact should also have left remnants of melted rocks and shocked
minerals, he said.

But if true, the hypothesis could explain the disappearance of Ice Age
mammals like mammoths and argue against the alternative idea that the
animals were hunted to extinction by humans.

It might also help explain the disappearance of the Clovis people, a culture
named after a distinctive arrow point discovered in a mammoth skeleton in
Clovis, N.M., who are believed to have arrived in the Americas more than
13,000 years ago.

Douglas J. Kennett, a University of Oregon
<http://topics.nytimes.com/top/reference/timestopics/organizations/u/univers
ity_of_oregon/index.html?inline=nyt-org>  archaeologist who is the lead
author of the Science paper, said no Clovis points or bones of the extinct
animals had been found above the diamond layer. “It seems those two things
synchronously end,” he said.

Dr. Kennett said there also appeared to be a gap of several centuries
between the disappearance of the Clovis and the resettlement by other
people.

Gary Huss, a scientist at the University of Hawaii
<http://topics.nytimes.com/top/reference/timestopics/organizations/u/univers
ity_of_hawaii/index.html?inline=nyt-org> , Manoa, who was one of the early
reviewers of the Science paper, said that while the scientists had not
proved their case, they had offered enough evidence that the idea warranted
a closer look by others.

“They have a hypothesis that explains several things that hard to explain
any other way,” he said. “Diamonds are less convincing by themselves, but
they strengthen their case considerably.”

 

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