Scientists drilling into Chesapeake meteor's crater

Cores produce wealth of information on supply of fresh water

September 09, 2001|By Robert S. Boyd | Robert S. Boyd,KNIGHT RIDDER/TRIBUNE

BAVON, Va. - It is so peaceful here, a flat green marsh bordering calm bay waters, lanky reeds, scrubby pines, gulls circling a distant lighthouse.

Only the clatter of a drilling rig breaks the spell, as scientists poke deep below the ground in search of traces of one of the greatest catastrophes ever to hit Earth.

Near this spot 35 million years ago, an enormous ball of ice or rock screeched down from outer space in a blinding flash of light and blasted a crater 56 miles across and almost a mile deep.

The meteor, the largest ever to strike what is now the United States, hurled fragments as far as Antarctica and gouged out a depression that lies under Chesapeake Bay, one of the East Coast's scenic wonders.

Today, a rough circle of low ridges in Virginia's coastal plain, near historic Williamsburg and Jamestown, marks the outer rim of the ancient crater, which is buried under thousands of feet of sand, silt and clay.

Effect on water supply

Other signs of the collision remain: Two million nearby residents face a shortage of fresh water, because the searing heat of the long-ago impact vaporized huge quantities of seawater, leaving the basin still filled with undrinkable salty water that threatens their freshwater aquifers. Nearby rivers make a peculiar sharp bend as they are diverted toward the sunken crater.

This summer, researchers from the U.S. Geological Survey havedrilled holes in and around the Chesapeake Bay Impact Crater, as it is known. They are trying to understand what happened when the meteor hit and what it means for people now and in the future.

Wylie Poag, a senior USGS scientist, pointed out that our planet is constantly pummeled by extraterrestrial objects, around 25,000 of them each year. Most are small and harmless. A little one bonked a boy on the head in Uganda in 1992, injuring him slightly; another bashed in a car fender in Peekskill, N.Y., the same year.

But it's only a matter of time, experts say, before another "big one" strikes, like the monster that rammed Earth off the coast of Mexico 65 million years ago.

Scientists think the long-lasting global climate change that followed that collision wiped out the dinosaurs and thousands of other species.

Speaking above the roar of the drill, Poag, who found and identified the Chesapeake crater in 1994, shows off a box of cylindrical cores pulled up from 2,000 feet below the ground. The muddy cylinders, each about the size and shape of a child's baseball bat, show rock that was twisted, jumbled and squeezed by the battering it endured long ago.

The hole here on the shore of the bay at Bavon is the latest of seven that researchers have punched into the ground so far. It lies between the inner and outer rings of rubble thrown up by the impact. Before quitting for the season this month, the crew plans to drill into the granite "basement" of the crater, a half-mile below the surface.

Scientists aren't certain whether the meteor was a comet, made mostly of ice, or an asteroid, a lump of stone or iron. At two to three miles in diameter, it was only a third the size of the Mexican dinosaur-killer. But when it crashed into the ocean here at 60,000 mph, it did awesome damage.

The splashdown caused a vast tidal wave that surged far inland into the Appalachian foothills. Such a wave, known as a super-tsunami, can tower more than a thousand feet, Poag said, as it roars into shallow water near the shore.

In addition, a hail of white-hot debris flung outward by the impact turned the Eastern United States into a wasteland. A cloud of dust encircled the globe, darkening the sky for months. The world's climate rapidly warmed and then cooled, perhaps contributing to a mass extinction of sea creatures a million years later.

Scale of annihilation

"Life on Earth would have been shocked, vaporized, pulverized, barbecued, blinded, irradiated, acidified, drowned, starved and frozen," Poag wrote in his book, Chesapeake Invader. "A similar strike in Chesapeake Bay today would wipe out all the major East Coast cities, killing tens of millions. . . . The scale of annihilation is appalling to contemplate."

Although the meteor rammed into the southern end of what is now Chesapeake Bay, it didn't directly create the magnificent estuary. The bay came into being only about 10,000 years ago, after the end of the last Ice Age.

That happened, Poag said, when water from melting ice sheets poured across the North American coastal plain, carving rivers through Pennsylvania, Maryland and Virginia on their way to the Atlantic. These rivers naturally converged on the lowest land they could find, which happened to be the basin created by the meteor millions of years earlier.

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