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Mega-crater linked to mass extinction before dinosaurs

June 4, 2006
Courtesy Ohio State University
and World Science staff

Scientists say they have found the Earth’s biggest known crater, and have linked it to the planet’s worst mass extinction. If they are right, the crater comes from to a meteor impact far more violent than one thought to have killed off the dinosaurs later.

A combined image of gravity fluctuations and airborne radar in the Wilkes Land region of East Antarctica . The edges of the crater are colored red and blue; a concentration of mantle material is colored orange (center). Image courtesy of Ohio State University.

The researchers reported finding the crater, 300 miles (482 km) wide, hidden beneath East Antarctic ice.

They said it may date back some 250 million years to the so-called Permian-Triassic extinction, when almost all animals died out. The event is thought to have cleared the way for the dinosaurs’ rise.

The crater is more than twice the size of the Yucatan peninsula’s Chicxulub crater, tied to an impact that may have killed off the great reptiles 65 million years ago. 

The bigger crater is estimated to be the result of a striking object some 30 miles (48 km) wide, compared to 6 miles (10 km) for the Chicxulub case.

Ralph von Frese and Laramie Potts of Ohio State University led a scientific team that identified the crater in East Antarctica’s Wilkes Land region, south of Australia. They reported the finding at the American Geophysical Union Joint Assembly meeting in Baltimore, Md. late last month.

They used NASA satellites to peer beneath Antarctic ice based on gravity measurements. The study found a huge plug of material from the Earth’s mantle, the layer of Earth between the crust and the core, which had risen up into the crust, in a formation about 200 miles (322 km) wide.

Such formations, called mass concentrations or “mascons,” are planetary equivalents of bumps on the head. They form when large objects hit, and the denser mantle bounces up into the crust above.

The scientists overlaid an image resulting from gravity measurements with airborne radar images of the ground beneath the ice. They found the mascon was centered in a circular ridge some 300 miles wide, enclosing a space larger than Ohio.

The ridge alone wouldn’t prove anything. But the addition of the mascon signaled “impact” to von Frese, who has studied moon craters for years. Such signals are open to interpretation, he admitted. But “we compared two completely different data sets taken under different conditions, and they matched.”

To date the impact, the scientists took a hint from the fact that the mascon is still visible. The Earth’s active geology normally scrubs away such formations eventually.

Based on the region’s known geologic history, “this Wilkes Land mascon formed recently by geologic standards—probably about 250 million years ago,” von Frese said. In another half-billion years, it will probably vanish, he added.

Its immediate effects would have devastated life, he said. “All the environmental changes that would have resulted from the impact would have created a highly caustic environment that was really hard to endure,” he said.

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