The 300-mile-wide crater lies hidden more than a mile beneath a sheet of ice and was discovered by scientists using satellite data, Ohio State University geologist Ralph von Frese said.
Von Frese said the satellite data suggests the crater could date back about 250 million years to the time of the Permian-Triassic extinction, when almost all animal life on Earth died out, paving the way for dinosaurs to rise to prominence.
The crater was found in what's known as the Wilkes Land region of the East Antarctic Ice Sheet.
"This is a strong candidate for the cause of the extinction," von Frese told The Associated Press in a telephone interview from Ohio.
"This Wilkes Land impact is much bigger than the impact that killed the dinosaurs, and probably would have caused catastrophic damage at the time," he said.
Similar claims were made in 2004 when a team led by Luann Becker of the University of California reported that a crater off the northwest coast of Australia showed evidence of a large meteor impact at the time of the early extinction.
That team relied heavily on core samples provided by an oil company drilling in the region as evidence for its findings.
The prevailing theory holds that the Permian-Triassic extinction was caused by 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 the Earth's climate.
Von Frese — who announced his findings last month at an American Geophysical Union meeting in Baltimore — acknowledged his discovery lacks such hard evidence. He said he wanted to visit Antarctica to hunt for rocks at the base of the ice along the coast that could be dated.
"There is skepticism and people are asking where is the other evidence and where are the rocks," he said. "You do want to have other evidence. The strongest evidence would be rocks from the event, including meteorite fragments."
Von Frese's findings so far rely on data from a NASA satellite that can measure fluctuations in gravity fields beneath the ice.
The data revealed a 200-mile-wide area where the Earth's denser mantle layer bounced up into the planet's crust. This is what would happen in reaction to such a big impact, in the planetary equivalent of a bump on the head, von Frese said.
When the scientists overlaid their gravity image with airborne radar images of the ground beneath the ice, they discovered imprints of lumps and ridges from the meteor that indicated impact. Von Frese has spent years studying similar impacts on the moon.
"There are at least 20 impact craters this size or larger on the moon, so it is not surprising to find one here," he said. "The active geology of the Earth likely scrubbed its surface clean of many more."
The crater's size and location, von Frese said, also indicated that it could have begun the breakup of the Gondwana supercontinent by creating a tectonic rift that pushed Australia northward.
Approximately 100 million years ago, Australia split from Gondwana and began drifting north away from what is now Antarctica, pushed by the expansion of a rift valley into the eastern Indian Ocean, von Frese said. The rift cuts directly through the crater, so the impact of the meteor may have helped the rift to form, he said.
By Michael Casey