[meteorite-list] Dinosaurs rocked!

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Thu, 04 Mar 2010 20:01:19 -0500
Message-ID: <csl0p51ghllnltgehv7ovm6m9kve8r0kvm_at_4ax.com>

Unless they were iced...

http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2010/03/04/BAFS1CADDJ.DTL

Settled: Dinosaurs done in by asteroid

David Perlman, Chronicle Science Editor

Thursday, March 4, 2010

(03-04) 15:09 PST SAN FRANCISCO -- What killed off all the dinosaurs?

Thirty years ago, UC Berkeley geologist Walter Alvarez offered his revolutionary
answer to that question and incited one of the liveliest controversies in modern
science.

Now an international team of scientists will report Friday that the issue is
settled: Alvarez was right.

In 1980, Alvarez and his colleagues at Berkeley theorized that a monstrous
asteroid 10 miles wide slammed into Mexico's Yucatan Peninsula and dug a crater
60 miles wide and 15 miles deep. The impact sent up a huge cloud of ash, soot,
pulverized rock and sulfurous steam that darkened the skies for years like a
nuclear winter, dooming more than half the world's life on land and in the
oceans - microorganisms, plants and animals.

The dinosaurs, those iconic beasts that had ruled the world for 160 million
years, also vanished in that long-lasting cataclysm, the Alvarez team
maintained.

They found worldwide layers of clay containing the rare metallic element iridium
that was scattered by the crashing asteroid; they found the crater caused by the
asteroid impact just off the Yucatan Peninsula at Chicxulub (pronounced
Chic-shoo-loob); and they found tiny spherules of shocked quartz both inside the
crater and far beyond the crash site, from Australia to Europe.

Scores of other scientists have found supporting evidence over the past three
decades and estimated that the asteroid impact set off earthquakes with
magnitudes as high as 11 -inconceivably greater than the quakes that have hit
Chile and Haiti.
The volcano theory

But there are disbelievers among other respected scientists who insist that
violent volcanic eruptions, not asteroids, caused what was one of the worst mass
extinctions in the world's history. Huge layers of volcanic rocks a mile thick
and covering nearly 200,000 square miles are still evidence of those eruptions
in an area of India known as the Deccan Traps, they say.

In Friday's report in the journal Science 41 noted scientists from a wide array
of disciplines declare that those espousing the volcano theory are wrong;
Alvarez and his team were right, they say.

The scientists work in every known discipline - geophysics, paleontology,
climatology, geochemistry, microbiology, zoology, botany and more. They have
re-worked the Alvarez team's findings, gathered new evidence and agree on their
conclusions.

In an e-mail interview Thursday, the leader of the group, Peter Shulte, said the
Chicxulub crater and its global distribution of shocked quartz form the
"fingerprint" backing the asteroid theory, and that the Deccan volcanism
actually started 700,000 before the mass extinction occurred.

The asteroid, he said, struck a sulfate-rich area that released masses of deadly
sulfur aerosols "leading to rapid darkness and cooling of the Earth."

"We conclude that a single impact was the ultimate cause for the mass
extinctions," said Shulte, a geophysicist at the University of
Erlangen-Nurnberg.

Kirk Johnson, a paleobotanist at the Denver Museum of Nature and Science who was
one of the journal authors, said of Alvarez and his many colleagues: "They got
it right; it was an inspired body of work."
Scientist unconvinced

But Gerta Keller, a Princeton paleontologist and geochemist who is a leading
expert on global catastrophes and mass extinctions and a supporter of the Deccan
Traps theory, is not convinced.

She argued in an interview this week that her team's evidence shows that the
Chicxulub impact occurred at least 300,000 years before the start of the mass
extinction; that the scientists responsible for Friday's Science article ignored
and misrepresented her group's evidence about the timing and effect of the
Deccan volcanism.

Those volcanoes, she said, emitted 30 times more global life-killing sulfur
fumes than any asteroid impact could; that 30 pulses of eruptions and lava flows
caused the mass extinction; and that the asteroid impact, whenever it happened,
caused no extinctions at all nor any change in the world's climate or
environment.

The real evidence for the mass extinction and the death of the dinosaurs still
lies in the vast basalts of the Deccan volcanoes, Keller insisted.

Now Alvarez has moved on to bigger things since he and his team published their
theories and added more details to support it. But Friday's report pleases him
greatly, he said.

"It's wonderful to see that our work is vindicated by such a large collection of
the very top people in all those fields," he said in an interview. "It's
gratifying indeed, but I've moved away from my love of geology these days, and
I'm interested in what we call Big History now - the entire history of the
cosmos, Earth, life and humanity. What a wonderful class to teach!"
Received on Thu 04 Mar 2010 08:01:19 PM PST