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Posted on 06/03/2006 3:23:27 PM PDT by NormsRevenge
WASHINGTON (AFP) - A meteor's roaring crash into Antarctica -- larger and earlier than the impact that killed the dinosaurs -- caused the biggest mass extinction in Earth's history and likely spawned the Australian continent, scientists said.
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.
Collaborators included Stuart Wells and Orlando Hernandez, graduate students in geological sciences at Ohio State; Luis Gaya-Pique and Hyung Rae Kim, both of NASA's Goddard Space Flight Center; Alexander Golynsky of the All-Russia Research Institute for Geology and Mineral Resources of the World Ocean; and Jeong Woo Kim and Jong Sun Hwang, both of Sejong University in South Korea.
They don't but oceanic magnetic stripes do (a recording by the solidifying rock at midocean ridges that records the magnetic field at time of extruding magma solifiying--since the magnetic field flips occasionally, they can be used to tell time). If this crater hit 250 million years ago along the plate boundary, there should be remnants 250 million years along the direction that the plates have moved, in both directions. This means that if you take a measurement of oceanic magnetic stripes you should be 250 million years to the plate boundary from the location of the current crater near Antarctica and another 250 million years to the plate boundary from other debris near Australia.
I agree. It was probably a "doublet" impact, that is, multiple, nearly simultaneous impacts from a large body torn apart by an earlier encounter, or by reaching its Roche point during terminal descent, or even more likely, by never having been a single body in the first place, a la TVF. :')
An Asteroid, Cobbled Together
ScienceNOW Daily News | 2 June 2006 | Phil Berardelli
Posted on 06/03/2006 3:34:15 AM EDT by neverdem
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