New! Sign up for our free email newsletter.
Science News
from research organizations

Mass Extinction's Cause: 'Sick Earth'

October 21, 2006
University of Southern California
The Permian-Triassic extinction is the largest recorded, more disastrous for life forms than the extinction that killed the dinosaurs. Its cause continues to be debated. USC earth scientists say their latest research points to gradual deterioration in the environment due in part to ocean warming.

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.

Story Source:

Materials provided by University of Southern California. Note: Content may be edited for style and length.

Cite This Page:

University of Southern California. "Mass Extinction's Cause: 'Sick Earth'." ScienceDaily. ScienceDaily, 21 October 2006. <>.
University of Southern California. (2006, October 21). Mass Extinction's Cause: 'Sick Earth'. ScienceDaily. Retrieved May 20, 2024 from
University of Southern California. "Mass Extinction's Cause: 'Sick Earth'." ScienceDaily. (accessed May 20, 2024).

Explore More

from ScienceDaily