By POH SI TENG
Published in The Columbus Dispatch
June 27, 2006
Shaped like a giant sombrero and buried beneath as much as 2 miles of ice in eastern Antarctica, this is the type of crater geophysicists dream about.
And this whopper belongs to Ralph von Frese, a geological sciences professor at Ohio State University.
Von Frese thinks the crater was caused by a meteor strike 250 million years ago that wiped out nearly all terrestrial life on Earth, setting the stage for the next big step in our planet’s evolutionary story: dinosaurs. Von Frese and colleagues say the impact was so big that it could have also been responsible for separating Australia from the Gondwana supercontinent.
“It may be the biggest impact crater found on Earth. It sort of puts our evolution into perspective,” said von Frese, who collaborated with geophysicists from Russia, Colombia, South Korea and Italy.
Located in Wilkes Land, Antarctica, the 312-mile-wide crater is twice the size of the Chicxulub crater in Yucatan, Mexico. The meteor that caused the Mexico impact is thought to have ended the dinosaurs’ reign 65 million years ago.
Despite the Antarctica crater’s immense size — scientists think the meteor that created it was as big as 30 miles wide — nobody knew it existed until von Frese found it.
But recent talk within the scientific community about a possible impact crater in Antarctica caught von Frese’s attention.
He began to search for an indentation in the icy continent in January 2005. Von Frese scouted for gravitational patterns similar to those of impact craters on the moon and Mars using twin NASA satellites called GRACE (Gravity Recovery and Climate Experiment).
After three months, von Frese and OSU postdoctoral researcher Laramie Potts found a candidate.
“I got Laramie to check things out, to see that I wasn’t imagining things,” von Frese said.
Using the GRACE satellites, they discovered something called mascons, concentrated masses beneath the Earth’s crust, said John LaBrecque, who directs NASA’s Earth Surface and Interior Focus Area.
Mascons form where large objects slam into a planet’s surface and the denser mantle layer is forced up into the overlying crust, which holds it in place beneath the crater.
Mascons resemble little mountains, Potts said.
The OSU research team said the crater in Wilkes Land might be linked to volcanic eruptions in the Siberian Traps lava planes. The eruptions, scientists think, were caused by the impact.
The fallout from the volcanic explosions is thought to have caused the Permian-Triassic extinction, also known as the “great dying.”
But some paleontologists say it is too early to connect the meteor that hit Wilkes Land to poisonous gases released on the other side of the globe.
“It is very speculative at this state,” said Jennifer McElwain, a paleobotany curator at the Field Museum in Chicago and a councilor for the Paleontological Society.
She said more ground-level studies are needed. Researchers first must confirm the age of the crater by analyzing rocks in the crust or along the Antarctic coastline, McElwain said.
Von Frese said he would like to work with other researchers and conduct more studies in Antarctica.
Australia split from Gondwana about 100 million years ago, drifting north into the eastern Indian Ocean after being pushed away by the expansion of a rift valley. The rift cuts directly through the crater, von Frese said, making the impact a prime suspect for helping the rift form.
The Wilkes Land discovery is crucial in understanding Earth’s history, said Thomas Wagner, director of the Antarctic Geology and Geophysics program for the National Science Foundation. The foundation and NASA funded the research.
“It’s the most exciting find under the ice in a few years,” Wagner said.