Crater Hunters Find New Clues to Ancient Impact Storm

livescience.com ^ | October 31, 2014 01:55pm ET | Becky Oskin, Senior Writer |

[BenLurkin]

Back when Wisconsin and western Russia once shared an address south of the equator, a violent collision in the asteroid belt blasted Earth with meteorites.

The space rock smashup showered Earth with up to 100 times more meteorites than today's rate (a rock the size of a football field hits the planet about every 10,000 years). Yet, only a dozen or so impact craters have been found from the ancient bombardment 470 million years ago, during the Ordovician Period. Most are in North America, Sweden and western Russia. There are only about 185 known impact craters on Earth of any age, while the moon has more than 100,000.

But the number of Ordovician craters may soon take off. That's because it's easier and cheaper than ever to hunt down evidence that confirms an impact. The clinchers include shocked minerals, deformed rocks and structural features that match other craters.

"Google Earth images are not good enough to identify an impact structure," noted planetary geologist Christian Köeberl on Oct. 22, at the Geological Society of America's annual meeting in Vancouver, British Columbia. During the Vancouver meeting, researchers presented new clues that bring suspected craters in Wisconsin, Kentucky and Tennessee closer to official listings as Ordovician impact craters.

The three enigmatic structures retain their circular shape, but have lost most of their original features through erosion. In the last century, quarrying has also slowly dismantled the Wisconsin crater. Only the central uplift seems to persist. When a meteorite hits, the impact's force causes the underlying rock to rebound upward, leaving a topographic high in the center of the crater.

[frithguild]

I was stuned!

Mush of what it threw was ice, because it hit in a glacier. Much of the “bow wake” that fell back to earth would have been slushy and not so rocky. To the west, much of what fell landed ontop of glaciers, so the evidence is minimal.

Cintos is non-academic, so this theory is very unpopular, which to me makes it even more interesting.

[SunkenCiv]

Thanks Robert A. Cook, PE. This is the best straight-up catastrophism topic in a while!

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[SunkenCiv]

I *thought* I’d felt something...

Thanks, nice graphic!

[JSteff]

“Most of western N. America didn’t even exist yet.”

That only makes sense silly.. Columbus had not even discovered America yet......