Stories tagged astroid

Jun
04
2006


Meteor Crater near Winslow, AZ: This crater formed when a meteor collided with Earth about 50,000 years ago. It is approximately 3/4 mile in diameter and 650 feet deep.
Courtesy Mark Ryan

A 300 mile wide crater (bigger than Ohio) has been detected beneath a half-mile of ice in Anartica. This crater is twice as big as the one thought to have killed the dinosaurs. Reseachers believe the impact may have broken up the Gondwana supercontinent, pushing what is now Australia northward.

Two separate data sets were combined to understand more about this impact. Radar to detect a crater, and gravity measurements to detect a mass concentration, or "mascon" in the same place. When a large mass slams into the earth, there is a rebound of mantle material up into the earth's crust creating a bump or mascon..

"On the moon, you can look at craters, and the mascons are still there," von Frese said. "But on Earth, it's unusual to find mascons, because the planet is geologically active. The interior eventually recovers and the mascon goes away." He cited the very large and much older Vredefort crater in South Africa that must have once had a mascon, but no evidence of it can be seen now.
"Based on what we know about the geologic history of the region, this Wilkes Land mascon formed recently by geologic standards -- probably about 250 million years ago," he said. "In another half a billion years, the Wilkes Land mascon will probably disappear, too." Ralph von Frese, a professor of geological sciences at Ohio State University

The Permian-Triassic extinction about 250 million years ago, when almost all animal life on Earth died out, may have resulted from this impact.

Not all scientists agree, however

Scientists contacted by [email protected] say they are sceptical, as no signs of such an enormous impact have been found in other, well-studied areas of Antarctica. Jane Francis, a geologist at the University of Leeds says, "That sequence has been worked on before, and no one has found evidence to support a massive impact like this," Paul Wignall, a palaeontologist at the University of Leeds, UK, who studies mass-extinction events says that few scientists will be convinced by the hypothesis until the team can precisely date their crater directly, and find rocks there that have been altered by the searing heat of the explosion.

Most think that the extinction started when a vast volcanic eruption released huge amounts of gas, including sulphur dioxide and carbon dioxide, into the atmosphere, causing acid rain and greenhouse warming. Von Frese notes that the explanations aren't mutually exclusive: the shockwaves from a huge impact could have travelled through the planet to trigger the eruptions in Siberia, delivering a devastating combination of disasters.

Too much ice covers the putative crater for a drilling expedition. But Von Frese hopes to make a research trip to Antarctica to look for rocks at the base of the ice sheet along the continent's coast that could attest to an impact.

Sources:
NatureNews
physorg
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