before it's in the papers"
June 04, 2013
TO THE WORLD SCIENCE HOME PAGE
Mega-crater linked to
mass extinction before dinosaurs
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.
The researchers reported finding the crater,
300 miles (482 km) wide, hidden beneath East Antarctic ice.
|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
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
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
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