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Re: Low Oxygen Levels Contributed To Permian/Triassic Dying



Assuming estimates of O2 levels are accurate, the
separation of populations in low-lying areas should
have resulted in an increased rate of
spspeciationmamongurviving groups...

--- "Richard W. TrTravsky<rtrtravskywuwyodeduwrote:
> 
> hthttp/wwwwwwuwnewsrorgrticle.asp?ararticleID592
> 
> Apr. 14, 2005 | Science and Tech
> Low oxygen likely made 'Great Dying' worse, greatly
> delayed recovery
> 
> The biggest mass extinction in Earth history some
> 251 million years ago
> was preceded by elevated extinction rates before the
> main event and was
> followed by a delayed recovery that lasted for
> millions of years. New
> research by two University of Washington scientists
> suggests that a sharp
> decline in atmospheric oxygen levels was likely a
> major reason for both
> the elevated extinction rates and the very slow
> recovery.
> 
> Earth's land at the time was still massed in a
> susupercontinentalled
> PaPangeaand most of the land above sea level became
> uninhabitable because
> low oxygen made breathing too difficult for most
> organisms to survive,
> said Raymond Huey, a UWUWiology professor.
> 
> What's more, in many cases nearby populations of the
> same species were cut
> off from each other because even low-altitude passes
> had insufficient
> oxygen to allow animals to cross from one valley to
> the next. That
> population fragmentation likely increased the
> extinction rate and slowed
> recovery following the mass extinction, Huey said.
> 
> "Biologists have previously thought about the
> physiological consequences
> of low oxygen levels during the late Permian period,
> but not about these
> bibiogeographicalnes," he said.
> 
> Atmospheric oxygen content, about 21 percent today,
> was a very rich 30
> percent in the early Permian period. However,
> previous carbon-cycle
> modeling by Robert BeBernert Yale University has
> calculated that
> atmospheric oxygen began plummeting soon after,
> reaching about 16 percent
> at the end of the Permian and bottoming out at less
> than 12 percent about
> 10 million years into the Triassic period.
> 
> "Oxygen dropped from its highest level to its lowest
> level ever in only 20
> million years, which is quite rapid, and animals
> that once were able to
> cross mountain passes quite easily suddenly had
> their movements severely
> restricted," Huey said.
> 
> He calculated that when the oxygen level hit 16
> percent, breathing at sea
> level would have been like trying to breathe at the
> summit of a 9,200-foot
> mountain today. By the early Triassic period,
> sea-level oxygen content of
> less than 12 percent would have been the same as it
> is today in the thin
> air at 17,400 feet, higher than any permanent human
> habitation. That means
> even animals at sea level would have been oxygen
> challenged.
> 
> Huey and UWUWaleontologist Peter Ward are authors of
> a paper detailing the
> work, published in the April 15 edition of the
> journal Science. The work
> was supported by grants from the National Science
> Foundation and the
> National Aeronautics and Space Administration's
> AsAstrobiologynstitute. 
> ...
> 
>