Digging back 35 million years in crater

Impact: Researchers plan to drill under the bay to look for pockets of a prehistoric ocean.

July 18, 2005|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

About 35 million years ago, a meteorite smashed into what is now the lower Chesapeake Bay with so much force that debris flew for thousands of miles.

This fall, scientists will try to figure out what else it did.

Researchers plan to drill more than a mile under the bay in Virginia to search for watery pockets of a prehistoric ocean, bacteria that thrive in boiling heat and clues about the meteorite that left a Rhode Island-sized dent in Earth's surface.

"Whatever we find is going to be interesting," said Charles Cockell, a professor of geomicrobiology at England's Open University.

Cockell, who met with U.S. scientists last month to discuss the drilling project, is coordinating the search for microscopic life amid the rocks and sediment that rushed into the crater in the moments after the impact.

Scientists believe that the mile-wide meteorite that splashed into the sea millions of years ago created a tsunami, shattered rocks and incinerated everything in its path as it plunged a mile below the surface.

"Material as big as houses flooded into the impact area," said Gregory S. Gohn, a U.S. Geological Survey geologist who is one of the scientists overseeing the project.

Since the bay impact crater was discovered in 1993, scientists have drilled at least 12 holes. But previous drilling projects were mainly designed to assess the crater's effect on groundwater supplies.

By going deeper and studying the microfossils, rocks and sediment they dig up, scientists hope to better determine how fast the meteorite was traveling, its size, its effect on surrounding rocks and whether it was an asteroid or comet.

More than 40 researchers from the United States, Austria, South Africa and Japan will also study the sediments and rocks to learn more about East Coast geology and Earth's climatic past. "It can tell us things about what sea levels and ice formations were like thousands of years ago and essentially how the climate has changed," said Kenneth Miller, chairman of geological sciences at Rutgers. He will examine rocks and sediment to look for patterns in Earth's climate history.

The $1.3 million drilling effort is being funded by the U.S. Geological Survey and the International Continental Scientific Drilling Program, a consortium of scientists that funds drilling projects at fault lines, volcanoes and craters around the world. Scientists will probably spend an additional $3 million conducting their own studies of the rocks and sediment dug up.

Beginning in September, crews will use a drill to dig 7,200 feet, deeper than they've gone before. They'll work about five miles north of the Cape Charles, Va., site where drillers reached a depth of 2,900 feet last year.

"We're hoping to get the best look yet at the impact the crater had on the environment back then and, really, the impact it still has today," said J. Wright Horton Jr., a USGS geologist.

The impact carved out geological rifts instrumental in creating the Chesapeake Bay. It also left a basin of sediment and seawater, which disrupts the flow of fresh water to aquifers, forcing nearby communities to build desalinization plants to treat their well water.

Researchers will dig through the crater into a region known as the "moat," which surrounds the crater's central core. By drilling there, they hope to hit pockets of ancient seawater left over from the impact and a mother lode of rocks and sediment.

"That's where the action is. That's where the most evidence is of alterations caused by the impact," said C. Wylie Poag, one of the USGS scientists credited with discovering the crater.

In 1983, Poag and others began to suspect that a huge meteorite had struck somewhere on the Eastern Seaboard. Microfossils and tiny stones collected by a drilling rig 90 miles off Atlantic City, N.J., matched material found at drill sites in the Gulf of Mexico and the Caribbean.

But the crater's location wasn't pinpointed until the 1990s, when sediment core samples taken near the mouth of the bay could be compared to marine seismic data pried out of Texaco and Exxon files by David Powars, a USGS geologist.

"I had to beg them for four years," Powars said.

The meteorite was probably vaporized on impact, Poag said. But researchers will look for trace elements of metals such as nickel and chromium that are common to asteroids. They will also study the size and shape of the shattered stones, calculating the amount of energy that pulverized them and, they hope, determining whether a comet or asteroid hit them. Comets generally travel faster than asteroids and can make a more substantial impact when they strike, Poag said.

The bay crater in Virginia is the largest in the United States and the sixth-largest of 170 known impact craters in the world. A number of factors make it an ideal place for exploration.

Because the meteorite struck in an ocean and remains covered by water, the site is better preserved than most impact craters. Also, the Eastern Shore location makes it accessible.

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