Unearthing Clues to a Cataclysm

"It was a very volatile impact," Powars said. Another big marine impact crater in the Barents Sea off the northern coast of Norway is named Mjolnir, for the legendary hammer of the Scandinavian god Thor. There, geologists believe, the impact temporarily ignited sediments on the bottom of the ocean.

The Chesapeake crater, which geologists describe as shaped like an upside-down broad-brimmed hat, is centered near Cape Charles and extends north along the Delmarva Peninsula to about Wachapreague, Va. It goes west across the bay into Gloucester County, south to Norfolk and east into the ocean.

Powars said he first suspected the crater after routine geological drilling in the area found disorganized sediments underground. It was revealed after oil company explorations showed the outline of a crater. The impact object, probably an asteroid, disintegrated, the geologists said, but traces of it might be found if the drilling reaches deep enough.

The crater has been extremely well preserved because it is buried under land and sea sediment, the geologists said. But it is accessible via land and could become among the most-studied in the world.

"I often say how much I would love to see [an impact like] this happen," Powars said, "as long as I was on something that keeps me alive."

Two years ago, a pair of California scholars, Steven N. Ward and Erik Asphaug, published a paper about the potential impact of an asteroid that scientists think has a minute possibility of striking Earth in 2880.

The asteroid, called 1950 DA, is about a half-mile in diameter. The two men calculated that if it struck the sea at 40,000 mph, 370 miles off the East Coast, it would blow an 11-mile hole in the sea floor and within two hours would send 300-foot tsunamis crashing against the coast from Cape Cod, Mass., to Cape Hatteras, N.C.

The chances of impact are highly remote, and their paper was just "a focus of thought," the authors wrote. "Humanity lives with a calculus of infinite devastation times infinitesimal probability."