Chain of Craters

Saturday, August 01, 1998
While visiting France a few years back, geologist John Spray of the University of New Brunswick in Canada chiseled some rock samples from the ancient Rochechouart crater in west-central France. Geologists had debated the crater's age for some time, and Spray wanted to use a new dating technique to settle the issue. His resultoan age of 214 million yearsoreminded him that the Manicouagan crater in Quebec was about that old. Intrigued, he did some more sleuthing and found three more craters of a similar age: Saint Martin, in Manitoba; Obolon, in the Ukraine; and tiny Red Wing, in North Dakota. Could all five craters have been created simultaneously? If so, it could explain a mass extinction of that age. David Rowley, a geophysicist at the University of Chicago who specializes in charting Earth's drifting tectonic plates, helped Spray determine where the craters would have been 214 million years ago. He found a remarkable pattern. As the map above shows, three of the craters line up in a neat row at latitude 22.8 degrees. Red Wing and Obolon fall slightly off that path. The likely explanation, says Spray, is that an asteroid broke up in space before hitting Earth. "It's highly unlikely," says Spray, "that the arrangement is coincidental."
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