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Re: P/T extinction linked to global warming



 Wasn't there a recent report of Lystrosaurus
surviving into the early Triasic?

--- GUY LEAHY <xrciseguy@prodigy.net> wrote:

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> Extinction Tied to Global Warming 
> Greenhouse Effect Cited in Mass Decline 250 Million
> Years Ago 
> By Guy Gugliotta
> Washington Post Staff Writer
> Friday, January 21, 2005; Page A03 
> 
> Scientists call it "the Great Dying," a 250
> million-year-old catastrophe that wiped out 90
> percent of ocean species and 70 percent of land
> species in the biggest mass extinction in Earth's
> geologic history.
> 
> The cause of this cataclysm is a matter of great
> dispute among paleontologists, but research released
> yesterday offers new evidence that global warming
> caused by massive and prolonged volcanic activity
> may have been the chief culprit.
> 
> Huge amounts of carbon dioxide were released into
> the air from open volcanic fissures known to
> geologists as the "Siberian Traps," researchers
> said, triggering a greenhouse effect that warmed the
> earth and depleted oxygen from the atmosphere,
> causing environmental deterioration and finally
> collapse.
> 
> A second set of findings suggested that the warming
> also crippled the oceans' ability to refresh their
> oxygen supply, causing the seas to go sterile,
> destroying marine life and allowing anaerobic
> bacteria (which do not require oxygen) to release
> poisonous hydrogen sulfide "swamp" gas into the air.
> 
> The two reports, prepared independently, both cast
> doubt on another theory -- that the Great Dying was
> caused by the impact of an asteroid or comet such as
> the one that triggered the extinction of the
> dinosaurs 65 million years ago. Both studies were
> published yesterday by Science Express, the online
> version of the journal Science.
> 
> "This is not a world that is happy and then goes
> 'Bang!' " said University of Washington
> paleontologist Peter D. Ward, leader of one of the
> two new studies. "This is a world that's in trouble
> for a long time, and then it gets in even worse
> trouble."
> 
> Ward led a team of scientists in a seven-year
> project to chronicle 126 fossil skulls in a
> 1,000-foot-thick deposit of sedimentary rock in
> southeastern South Africa's Karoo Basin. He said in
> a telephone interview that the samples included
> reptiles and some amphibians, ranging from dog-size
> animals to predatory gorgonopsians, which he
> described as "a hideous cross between a lion and a
> particularly nasty lizard."
> 
> Ward said the team's excavations showed a steady
> decline in the number of species over 10 million
> years, followed by a sudden plunge 250 million years
> ago at the boundary between the Permian and Triassic
> periods of geologic time. The interval corresponds
> to a period of prolonged volcanic activity over
> one-third of modern-day Siberia.
> 
> Temperatures climbed globally as carbon dioxide
> poured into the atmosphere and oxygen levels fell,
> forcing gasping animals to gather at sea level, he
> said. "And the plants are not dealing well with the
> heat" either, he added. "Eventually the imbalance
> reaches a critical point, and everything dies."
> 
> The warming also meant that polar oceans were not
> cooled as much as they are today, and the convection
> cycle that circulates cold, oxygen- and
> nutrient-rich water between the poles and the
> tropics was slowed and even stopped, according to
> the second paper by a team of researchers led by
> Kliti Grice of the Curtin University of Technology
> in Perth, Australia.
> 
> "This has devastating effects on the marine
> organisms that rely on oxygen and nutrients to
> survive," the team said in an e-mail. "In the
> worst-case . . . a major part of the water column
> above the sea floor is devoid of oxygen."
> 
> Analyzing sulfur and carbon isotopes from core
> samples taken from the ocean bed off the coast of
> northwestern Australia, the team detected molecular
> traces from green sulfur bacteria, known as
> Chlorobiaceae, at the time of the Great Dying.
> 
> "The beauty of these [bacteria] is that they require
> sunlight and an anoxic [oxygen-free] environment,"
> said team member Steven Turgeon, an Oak Ridge
> National Laboratory geochemist. "Because they live
> so close to the surface, we're pretty sure that
> what's beneath is anoxic."
> 
> This combination of factors, which has also been
> detected in waters off southern China, indicates
> that large swatches of ocean below a depth of 300
> feet -- the deepest that significant light can
> penetrate -- became sterile, and that the entire
> ocean may have been oxygen-free.
> 
> Just as important, the bacteria derive energy from
> sulfate compounds in seawater and vent poisonous
> hydrogen sulfide gas into the air, Turgeon noted in
> a telephone interview.
> 
> The Grice team did not address the cause of the
> lethal warming, but Ward said his team found no
> evidence of the residue that would have fallen after
> a comet or asteroid impact threw tons of dust into
> the air to trigger a sudden and catastrophic
> greenhouse effect.
> 
> Still, University of Rochester earth scientist
> Robert Poreda, a proponent of the impact theory,
> noted that the "absence of evidence" at Karoo Basin
> "does not constitute evidence of absence."
> 
> "We propose there was preexisting volcanism" that
> became much worse because of the seismic energy
> released by the asteroid or comet impact, he said.
> "Some people have thought it feasible, while others
> have been adamantly opposed."
> 
> 



                
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