Australia's meteoric rise from Gondwana
A METEOR believed to have caused the biggest mass extinction in Earth's history, long before dinosaurs roamed the planet, may have also spawned the Australian continent, US scientists have revealed.
A geological team from Ohio State University, which collaborated with NASA, said it was likely the impact of the meteor about 250 million years ago jump-started the break-up of the Gondwana supercontinent that led to the creation of modern Australia.
Australia separated from Gondwana about 100 million years ago and began drifting northward, pushed away by the expansion of a rift valley into the eastern Indian Ocean.
"Its size and location — (of the impact) in the Wilkes Land region of East Antarctica, south of Australia — suggest that it could have begun the break-up of Gondwana supercontinent by creating the tectonic rift that pushed Australia northward," the team's leader Ralph von Frese said in a statement.
"The rift cuts directly through the crater, so the impact may have helped the rift to form."
The crater, which is about 483 kilometres wide and hidden more than 1.6 kilometres beneath the East Antarctic ice sheet, is twice the size of the Chicxulub crater in Mexico's Yucatan peninsula that marks the impact that scientists say may have ultimately killed the dinosaurs 65 million years ago.
"The Wilkes Land impact is much bigger than the impact that killed the dinosaurs, and probably would have caused catastrophic damage at the time," Professor von Frese said.
The scientists presented their preliminary findings at a recent American Geophysical Union Joint Assembly meeting. They used gravity fluctuations measured by NASA's satellites to peer beneath Antarctica's icy surface, finding a 321-kilometre-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 centred inside a circular ridge some 483 kilometres wide — large enough to hold Tasmania.
Taken alone, the ridge structure wouldn't prove anything. But to Professor von Frese, the addition of the mascon means "impact".
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