[meteorite-list] Low Oxygen Likely Made 'Great Dying' Worse, Greatly Delayed Recovery

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Apr 19 16:27:09 2005
Message-ID: <200504192012.j3JKCLV15357_at_zagami.jpl.nasa.gov>

http://www.uwnews.org/article.asp?articleID=9592

Low oxygen likely made 'Great Dying' worse, greatly delayed recovery
University of Washington
April 14, 2005

CONTACT: Vince Stricherz
vinces_at_u.washington.edu
206-543-2580

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 supercontinent called
Pangea, and 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 UW biology 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
biogeographical ones," 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 Berner at 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 UW paleontologist 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 Astrobiology
Institute.

Not only was atmospheric oxygen content dropping at the end of the
Permian, the scientists said, but carbon dioxide levels were rising,
leading to global climate warming.

"Declining oxygen and warming temperatures would have been doubly
stressful for late Permian animals," Huey said. "As the climate warms,
body temperatures and metabolic rates go up. That means oxygen demand is
going up, so animals would face an increased oxygen demand and a reduced
supply. It would be like forcing athletes to exercise more but giving
them less food. They'd be in trouble."

Ward was lead author of a paper published in Science earlier this year
presenting evidence that extinction rates of land vertebrates were
elevated throughout the late Permian, likely because of climate change,
and culminated in a mass extinction at the end of the Permian. The
event, often called "the Great Dying," was the greatest mass extinction
in Earth's history, killing 90 percent of all marine life and nearly
three-quarters of land plants and animals.

Ward said paleontologists had previously assumed that Pangea was not
just a supercontinent but also a "superhighway" on which species would
have encountered few roadblocks while moving from one place to another.

However, it appears the greatly reduced oxygen actually created
impassable barriers that affected the ability of animals to move and
survive, he said.

"If this is true, then I think we have to go back and look at oxygen and
its role in evolution and how different species developed," Ward said.
"You can go without food for a couple of weeks. You can go without water
for a few days. How long can you go without oxygen, a couple of minutes?
There's nothing with a greater evolutionary effect than oxygen."

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Received on Tue 19 Apr 2005 04:12:21 PM PDT