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.

[JimRed]

Weathering quickly (in geological terms, over hundreds of thousands of years) erases evidence of all but the largest of impact craters.

[Robert A Cook PE]

I have long been suspicious of the curiously-circular edges of Lakes Michigan-Huron, with the Michigan peninsula showing up as the rebounding central mountain range typical of craters.

[eyeamok]

Yet, only a dozen or so impact craters have been found from the ancient bombardment 470 million years ago

Evidence destroyed by Climate Change/s

[frithguild]

Saginaw Impact hypothesis http://cintos.org/SaginawManifold/Saginaw_Bay/index.html

[CPT Clay]

Geology ping
It is in the tagline

[Cold Heart]

“I have long been suspicious of the curiously-circular edges of Lakes Michigan-Huron,..”

Educational program on TV about salt mining under the great lakes. The salt mine deposit is circular under the area you describe. It is immense. No mention of the cause for that in the program.

[Don Corleone]

Erosion, global warming and of course Bush’s fault caused the craters to disappear.

[Pete from Shawnee Mission]

Diane! Its like holes in swiss cheese!

http://www.homefacts.com/earthquakes/Wisconsin/Door-County/Brussels.html (Good news! no earthquakes in Brussels WI!)

I think its located around Lovers lane and Gravel Pit Road in Brussels. The circular forested area might be it, but there are cliffs near gravel pit road!

[jmacusa]

The Earths atmosphere and natural erosion tends to remove craters where the Moons lack of an atmosphere preserves them.

[Robert A Cook PE]

Good find. Interesting, well-developed hypothesis!

(Particularly since I’m working INSIDE the Saginaw Crater right now at Bay City, Saginaw, and Midland. But there are extensive oil fields right here, and across lake Huron in Canada. Would not a meteor impact that recent have destroyed those fields?)

[frithguild]

The hypothesis is that the impact was highly oblique, sat five degrees. Think about what the bow of s boat does throwing material off to either side. Thus the Carolina Bay geology

[Diana in Wisconsin]

This can’t be possible, as the Earth is only about 4,000 years old. *SMIRK*

This stuff is amazingly interesting! Thanks for the PING, Pete! :)

[uglybiker]

Not to mention plate tectonics.

[Paladin2]

THIS is hugh:

[jmacusa]

“Not to mention plate tectonics’’. Yup. But as to impact craters I remember reading somewhere that a good part of what is now southern Florida particularly in the Everglades is the remains of a large impact crater. Who knows, maybe the chunk of rock that hit the Yucatan sixty-five million years ago might have had something traveling with it or debris thrown upward hit southern Florida.... fascinating stuff.

[jmacusa]

Of course! Bush’s fault! Thank you Don Corleone for reminding us of that. It’s been a little too long that ol’ G.W hasn’t been being properly held to account.

[jmacusa]

Smarty pants, everyone knows the Earth is 5,000 years old. :-)

[uglybiker]

True, but the craters mentioned in the article are supposedly 470myo. A lot has happened since then. Oceans have advanced and receded. Mountain ranges rised and weathered away. Most of western N. America didn’t even exist yet.

[jmacusa]

Indeed. Like I say, fascinating stuff. Astronomy is a hobby of mine.