[meteorite-list] Permian-Triassic Mass Extinction Cause: 'Sick Earth'

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri Oct 20 16:52:40 2006
Message-ID: <200610202052.NAA06312_at_zagami.jpl.nasa.gov>

http://www.eurekalert.org/pub_releases/2006-10/uosc-mec102006.php

Public release date: 20-Oct-2006

Contact: Carl Marziali
marziali_at_usc.edu
213-740-4751
University of Southern California

Mass extinction's cause: 'Sick Earth'

USC earth scientists turn up clues to explain disappearance of 90
percent of ancient species

What really caused the largest mass extinction in Earth's history?

USC earth scientists will reveal new clues at the annual meeting of the
Geological Society of America in Philadelphia Oct. 22-25.

The Permian-Triassic extinction, as it is called, is not the one that
wiped out the dinosaurs. Nor does the cause appear to have been a
meteorite strike, as in that famous event.

The most likely explanation for the disappearance of up to 90 percent of
species 250 million years ago, said David Bottjer, is that "the earth
got sick."

Bottjer, professor of earth sciences in the USC College of Letters, Arts
and Sciences, leads a research group presenting several new pieces of
the P-T extinction puzzle.

Matthew Clapham, a recent Ph.D. graduate of Bottjer's laboratory, has
found that species diversity and environmental changes were "decoupled"
long before the extinction. Conditions on the planet were deteriorating
long before species began to die off, Bottjer said, casting doubt on the
meteorite strike theory.

"People in the past used to think this big mass extinction was like a
car hitting a wall," he said. Instead, Clapham's interpretation of the
geological record shows "millions of years of environmental stress."

Pedro Marenco, a doctoral student in Bottjer's lab, has been testing a
leading theory for the P-T extinction: that a warming of the earth and a
slowdown in ocean circulation made it harder to replace the oxygen
sucked out of the water by marine organisms. According to the theory,
microbes would have saturated the water with hydrogen sulfide, a highly
toxic chemical.

For a mass extinction "you really needed a good killer, and it [hydrogen
sulfide] is really nasty stuff," Bottjer said.

Marenco has measured large changes in the concentration of sulfur
isotopes that support the hydrogen sulfide theory.

###

Bottjer is slated to chair a symposium on the P-T extinction and, in a
related presentation, to propose the Moenkopi geological formation in
the American Southwest as a promising candidate for studying the
extinction through analysis of the different stresses on land and sea
during that period.

Bottjer's symposium, as well as his and Marenco's presentations, take
place Oct. 24. Clapham presents his results Oct. 22.
 
Received on Fri 20 Oct 2006 04:52:35 PM PDT