‘Great Dying’ linked to
climate changes
Two teams of scientists point to volcanic
eruptions rather than asteroid as cause of
the Permian mass extinction 250 million
years ago
There has been recent evidence that a big
asteroid or meteor hit the Earth and
triggered the catastrophe, but researchers
say they now have evidence that something
much more long-term was the culprit.
Kliti Grice of Curtin University of
Technology in Perth, Australia, and
colleagues studied sediment cores drilled
off the coasts of Australia and China and
found evidence that the ocean was lacking
oxygen and full of sulfur-loving bacteria at
that time.
This finding would be consistent with an
atmosphere low in oxygen and poisoned by
hot, sulfurous, volcanic emissions, they
wrote in a report published in the journal
Science.
Gradual die-off
A second team, led by Peter Ward at the
University of Washington, looked at fossil
evidence in South Africa — they found little
evidence of a sudden catastrophe but
instead saw signs of a gradual die-off.
Roger Smith of the South African Museum and Peter
Ward of the University of Washington show off the
fossil of a gorgonopsid, a predator that disappeared
about 250 million years ago in the Permian -Triassic
mass extinction. The fossil was discovered in the
Karoo region of South Africa.
MSNBC staff and news service reports
Updated: 2:20 p.m. ET Jan. 20, 2005
Atmospheric changes related to volcanic
eruptions, and not a giant asteroid, were
probably the main factors behind Earth's
biggest die-off about 250 million years ago,
according to two separate teams of
scientists working at sites around the globe.
The mass extinction, known as the “Great
Dying,” extinguished 90 percent of sea life
and nearly three-quarters of land-based
plants and animals.
They examined 126 reptile and amphibian
skulls from the Karoo Basin in South Africa,
where there is an exposed piece of dried
sediment from the end of the Permian Era
and the beginning of the Triassic, 250
million years ago.
They found two patterns, one showing
gradual extinction over about 10 million
years leading up to the time of the
extinction, and then a spike in extinction
rates that lasted another 5 million years,
Ward’s team reported.
“Animals and plants both on land and in the
sea were dying at the same time, and
apparently from the same causes — too
much heat and too little oxygen,” Ward said
in a statement.
Ward believes mass volcanic eruptions may
have pumped greenhouse gases into the
air, which would have trapped heat in the
atmosphere and raised temperatures.
'Double-whammy' at work
“I think temperatures rose to a critical
point. It got hotter and hotter until it
reached a critical point and everything
died,” Ward said. “It was a double-whammy
of warmer temperatures and low oxygen,
and most life couldn’t deal with it.”
according to Ward, lower sea levels,
perhaps caused by plate tectonics, exposed
wide stretches of sea sediment to the air.
The resulting chemical reaction between
oxygen in the atmosphere and carbon in
the sediments produced carbon dioxide and
used up oxygen.
"When that stuff hit the air, it started
sucking the oxygen out," Ward said. That
"suck-down" of oxygen had a suffocating
effect on land animals, he said.
What about an asteroid?
Last May, researchers said they found
evidence of a giant asteroid striking Earth
off the coast of what is now Australia 251
million years ago, and suggested that the
impact may have played a role in the
Permian-Triassic extinction. Others have
disputed their conclusions however, and no
one has been able to confirm their results.
The Permian-Triassic extinction opened the
way for the rise of dinosaurs — which
themselves fell victim to another mass dieoff 65 million years ago. Most experts agree
that the catastrophic impact of a massive
asteroid or crater played the primary role in
that extinction, at the boundary between
the Cretaceous and Tertiary geologic
periods. The blast is thought to have
formed the Chicxulub crater off Mexico’s
Yucatan Peninsula.
This report includes information from
Reuters and The Associated Press as well as
from MSNBC's Alan Boyle.
© 2005 MSNBC Interactive
After reading this article, prepare a
homework paper and answer the following
questions. Be sure to copy or restate the
question as part of your answer!
1. What was the largest mass extinction in
Earth’s history?
2. What percentage of species died out?
3. Where were researchers Peter Ward and
Roger Smith studying fossils to learn
about this extinction? What patterns in
the extinction did they discover?
4. What do researchers Ward and Smith
believe caused this?
5. What is thought to have caused this mass
extinction? What geological events may
have triggered it?
6. Could humans survive events like those
that may have caused this mass
extinction? If so, how?
7. What other theory has been proposed to
explain this event? Would this other
cause produce a pattern of extinction like
the one discovered by Ward and Smith?