WASHINGTON — Millions of years before the dinosaurs vanished, an even bigger mass extinction wiped out more than 90 percent of the species on Earth. Now scientists think they may have evidence of an impact crater that contributed to the “Great Dying.”
The Permian-Triassic extinction took place 250 million years ago in a vastly different world from today's. Scientists have debated its cause for years.
The end of the dinosaurs 65 million years ago is widely thought to have been caused by a meteor impact off Mexico’s Yucatan Peninsula.
A team led by Luann Becker of the University of California, Santa Barbara, reported in Friday’s issue of the journal Science that a crater off the northwest coast of Australia shows evidence of a large meteor impact at the time of the early extinction.
They call it Bedout Crater (pronounced Beh-doo).
Vital to their conclusion was the discovery that core samples had been drilled in the region in the search for oil.
She said her team was “flabbergasted” when they looked at the never-before-studied cores, which contained meteorite fragments, “shocked” quartz and other impact evidence.
In addition, quartz and other minerals blasted out by the impact have been found in Australia, Antarctica and possibly India, said Kevin Pope of Geo Eco Arc Research, a private geological research company in Aquasco, Md.
The impact occurred at the right time, so it is a good candidate for the cause of the extinction, said Robert Poreda of the University of Rochester, N.Y.
The prevailing theory about the cause of this extinction had blamed a series of volcanic eruptions over thousands of years that buried what is now Siberia in molten rock and released tons of toxic gases into the atmosphere, changing Earth’s climate.
The new find provides “suggestive ... but perhaps not yet compelling evidence” that an impact was involved, said Douglas H. Erwin, a senior paleobiologist at the Smithsonian’s National Museum of Natural History.
This mass extinction was a fundamental transition in the history of life on Earth, Erwin said. He said further study will be done to try to confirm the new theory.
One difficulty, he said, is that there was a complex set of events occurring at the same time, including the eruptions in Siberia.
Perhaps more than one factor was involved, Becker said. “We think that mass extinctions may be defined by catastrophes like impact and volcanism occurring synchronously in time,” Becker said.
Other scientists are skeptical.
“It’s not yet persuasive that it’s even a crater,” said Peter D. Ward, a professor of geological sciences at the University of Washington in Seattle who has long studied impact craters and mass extinctions.
Intensive study is required to join the list of the world’s proven impact craters. Most have been eroded by rain, wind and earthquakes over millions of years. This possible new site is poorly preserved and deeply buried.
Even if it is an impact crater, size must be proved, Ward said. “It’s got to be a big hit” to cause global repercussions, he said. “There’s going to have to be a tremendous amount of more work” done on the site.
Becker’s team was funded by NASA and the National Science Foundation.
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