June 16, 2006 at 8:39 pm #14824
Planetary scientists have found evidence of a meteor impact much larger and earlier than the one that killed the dinosaurs–an impact they believe caused the biggest mass extinction in Earth’s history.
The 300-mile-wide crater lies hidden more than a mile beneath the East Antarctic Ice Sheet. The 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.
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. The image above shows the thickness of the Earth’s crust across Antarctica with thicker crust colored in red. The location of the Wilkes Land crater is circled (below right of center).
The gargantuan crater is more than twice as large as the crater in the Yucatan peninsula formed by the meteor that is thought to have killed the dinosaurs some 65 million years ago. “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 The Ohio State University in Columbus, who along with a team from NASA and international partners in Russia and Korea, discovered the crater.
How did they find the crater when it’s covered by ice and snow? The scientists used gravity fluctuations measured by NASA’s GRACE satellites to peer beneath Antarctica’s icy surface and discovered a 200-mile-wide plug of mantle material–a mass concentration, or “mascon” in geological parlance–that had risen up into the Earth’s crust. Mascons are the planetary equivalent of a bump on the head. They form where large objects slam into a planet’s surface. Upon impact, the denser mantle layer bounces up into the overlying crust, which holds it in place beneath the crater. When the scientists overlaid their gravity image with airborne radar images of the ground beneath the ice, they found the mascon perfectly centered inside a circular ridge some 300 miles wide–a crater easily large enough to hold the state of Ohio.
But out of death comes life. The impact would have utterly 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,” said von Frese. Still, scientists believe that the cataclysmic extinction caused by the meteor smashing into Antarctica paved the way for the dinosaurs to rise to prominence.
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