Ohio State University scientists said the 483-kilometer-wide (300-mile-wide) crater is now hidden more than 1.6 kilometers (one mile) beneath the East Antarctic Ice Sheet.
"Gravity measurements that reveal its existence suggest that it could date back about 250 million years -- the time of the Permian-Triassic extinction, when almost all animal life on Earth died out," the university said in a statement Thursday.
"Its size and location -- in the Wilkes Land region of East Antarctica, south of Australia -- also suggest that it could have begun the breakup of the Gondwana supercontinent by creating the tectonic rift that pushed Australia northward," they added.
Scientists believe that the Permian-Triassic extinction paved the way for the dinosaurs to rise to prominence.
The Wilkes Land crater is more than twice the size of the Chicxulub crater in Mexico's Yucatan peninsula, which marks the impact that may have ultimately killed the dinosaurs 65 million years ago.
The Chicxulub meteor is thought to have been 9.6 kilometers (six miles) wide, while the Wilkes Land meteor could have been up to 48.3 kilometers (30 miles) wide -- four or five times wider.
"This Wilkes Land impact is much bigger than the impact that killed the dinosaurs, and probably would have caused catastrophic damage at the time," said Ralph von Frese, a professor of geological sciences at Ohio State.
He and Laramie Potts, a postdoctoral researcher in geological sciences, led the team that discovered the crater. They collaborated with other Ohio State and NASA scientists, as well as partners from Russia and South Korea. They reported their preliminary results in a recent American Geophysical Union Joint Assembly meeting in Baltimore, Maryland.
Some 100 million years ago, Australia split from the ancient Gondwana supercontinent and began drifting north, pushed away by expansion of a rift valley into the eastern Indian Ocean. The rift cuts directly through the crater, so the impact may have helped the rift to form, von Frese said.
The more immediate effects of the impact, however, would have devastated life on Earth. "All the environmental changes that would have resulted from the impact would have created a highly caustic environment that was really hard to endure. So it makes sense that a lot of life went extinct at that time," he said."