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Giant crater may lie under Antarctic ice

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Adam Hawthorne
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« on: June 02, 2007, 09:06:33 pm »

Giant crater may lie under Antarctic ice
18:50 02 June 2006
NewScientist.com news service
Damian Carrington


A huge potential crater has been discovered in Antarctica via gravity measurements from space. The find has led geologists to speculate that the huge meteorite that may have caused it prompted the biggest mass extinction in the Earth's history and caused the break up of an early supercontinent, spawning Australia.

The gravity measurements were obtained by the GRACE satellites and show a 300-mile-wide (483km) structure that is now hidden more than one mile (1.6 km) beneath the East Antarctic Ice Sheet (see diagram).

Ralph von Frese, at Ohio State University in the US, and colleagues say the Wilkes Land crater is more than twice the size of the Chicxulub crater in Mexico's Yucatan peninsula, which marks the impact that is thought to have killed off the dinosaurs 65 million years ago.

While the meteorite that created the Chicxulub crater is thought to have been six miles (9.6 km) wide, the Antarctic meteorite could have been up to 30 miles wide (48.3 km). But while von Frese is hopeful, the Antarctic structure is not necessarily the result of an impact - it could have been caused by normal volcanic activity. Only rocks samples from the area showing evidence of an impact will resolve the issue.

Softened bruises
Determining when the structure formed is difficult, but the researchers have put rough bounds on the date. The crater is cut by the rift which opened to form the Indian Ocean, meaning it must be older than 100 million years.

And von Frese told New Scientist that impact craters older than the start of the Cambrian geological period 543 million years ago no longer have gravity anomalies. "They are like bruises big in the beginning but they get smaller with time", he says, as the crust erodes and creeps to fill in the depression.

In between those two dates, 250 million years ago, the end of the Permian period marked the greatest die-off of species ever seen. Von Frese thinks the discovery of the massive crater that could have been created at the right time is suggestive, but admits there is no proof. Other researchers have suggested a structure off the Australian coast could be an impact crater linked to the Permian mass extinction.

He would like to visit Antarctica to perform gravity and magnetic surveys using a long-range aircraft. Such an expedition would also allow geologists to see whether glaciers draining the basins over the crater have eroded and carried rock samples to the coast.

Big hit
Von Frese also thinks it is possible that the impact actually prompted the break up of the supercontinent Gondwanaland, which created Australia, Africa and India. And he notes that the Siberian traps, a series of huge volcanic eruptions is on exactly the opposite side of the globe from the Antarctic crater.

But he acknowledges that this idea is controversial (see a previous New Scientist story) and that geologists are far from agreement: "It's a poorly studied phenomenon."

They research was reported at a recent American Geophysical Union Joint Assembly meeting in Baltimore, Mary

http://space.newscientist.com/article/dn9268

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Adam Hawthorne
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« Reply #1 on: June 02, 2007, 09:07:40 pm »



Gravity data from the GRACE satellites (denser regions in red) show the location of the Wilkes Land crater (above centre) (Image: Ohio State University)
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Adam Hawthorne
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« Reply #2 on: June 02, 2007, 09:08:57 pm »



This map of the thickness of the Earth's crust across Antarctica (thicker crust in red) also shows the Wilkes Land crater (below right of centre) (Image: Ohio State University)
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