THE VIRGINIAN-PILOT
Copyright (c) 1994, Landmark Communications, Inc.
DATE: Saturday, August 27, 1994 TAG: 9408270226
SECTION: FRONT PAGE: A16 EDITION: FINAL
SOURCE: BY JAMES SCHULTZ, STAFF WRITER
LENGTH: Long : 111 lines
A meteorite the size of a small mountain slammed into what's now Virginia some 35 million years ago, helping to form the Chesapeake Bay, scientists from the U.S. Geological Survey have concluded in a just-released study.
Examining drilling samples and other geologic evidence from around the Bay, the scientists found evidence of a meteor crater that would be the largest discovered in the United States, the sixth-largest in the world. Their findings are published in this month's edition of the journal Geology.
The meteorite, a mile in diameter and traveling between 6 and 12 miles per second, would have landed just west of present-day Cape Charles, gouging an impact crater 1 1/2 times the size of Rhode Island.
``Every once in a while I sit back and try to imagine what it would have been like,'' said the leader of the scientific team, geologist J. Wylie Poag. ``It's such an abnormal thing in terms of human experience - an object that large slamming into the Earth and digging a hole 50 miles across. It's really astonishing.''
A large, shallow inland sea then covered most of what is now eastern Virginia. The collision would have sent enormous tidal waves, perhaps as high as 1,600 feet, racing to tear at the coastline located west of what is now Richmond, in the foothills of the Appalachians. The cosmic crash would have sent debris hurtling through the atmosphere as far north as New Jersey, as far south as Barbados, and as far west as Texas, covering an area of nine million square miles.
Rocks would have melted and minerals fused in the extremely high temperatures and pressures created at ground zero of the blast. A blanket of silt, sediment and fractured boulders would have been thrown up and away from the immediate crater, draping itself over hundreds of square miles around the crater's edge.
Many of the creatures languishing in the sea near today's Eastern Shore - ancestors of fish, sharks, lobsters, crabs, and clams - would have perished instantly.
Poag and his colleagues first realized that they might be on to something when, several years ago, samples that they drilled in southern Virginia revealed unusually jumbled sediments and boulders. Subsequent seismic studies of rocks beneath the Chesapeake Bay revealed fault lines that corresponded to those that were produced by the impact of a large meteorite.
``Meteor'' is the word for any object - rock, metal or ice - that passes from space through air. ``Meteorite'' is reserved for any chunk that reaches Earth in one piece.
Fragments of comets, asteroids and debris left over from the formation of the solar system rain down on Earth continually. On average, 20 tons of heavenly junk daily fall through, and burn up in, the upper reaches of the atmosphere.
Only the really big meteors survive most of the passage, and nearly all of those disintegrate before they reach the ground. Those that do survive the fiery descent can mortally wound planetary plant and animal life.
``This is substantiation that the Earth continues to be hit by meteors,'' said Gerald H. Johnson, a William and Mary geology professor. ``Some of them are pretty darn big.''
The biggest so far appears to be a 6-mile-wide asteroid or comet (scientists still haven't decided which) that has been implicated in the mass extinction of the dinosaurs 65 million years ago. The rocky object hit near the present-day Yucatan Peninsula in Mexico with an estimated force of 100 million tons of TNT, sending a shock wave that is believed to have leveled anything standing within a 150-mile radius.
The resulting crater - the outlines of which have yet to be completely mapped - is thought to measure 180 miles in diameter.
Scientists believe two-thirds of the species then living, plant and animal, died when dust thrown up from the mega-explosion obscured the sun, preventing photosynthesis and dramatically cooling planetary temperatures.
In 1908, 700 square miles of virgin timber was leveled in Siberia when an asteroid or comet exploded five miles above the ground. Animals were killed more than a dozen miles from the blast, and one man reported that his clothes caught fire even though he was 60 miles away.
Worldwide, there are about 140 meteorite impact craters that attest to the power of the skies to determine destinies on the ground. Researchers believe they may find more such scars, as ground radars and scanning technologies improve.
Not all scientists are convinced Poag and company are right. Needed to sway any skeptics is hard evidence, in the form of ``shocked'' minerals that display characteristic patterns obtained only in the presence of a very powerful explosion. Another sign of a meteorite is a higher-than-normal concentration of the metallic element iridium.
When Johnson of William and Mary learned of the finding, he headed out to the field for experimental verification. He and his students will be studying the alleged edge of the meteorite impact field, focusing on an area from James City County to Chuckatuck, just south of Smithfield. Professor and pupils will examine sediments and boulder fields for definitive proof of the astral impact.
``This is a nice little pothole,'' Johnson said. ``It explains some of the things we (geologists) have had problems with. It's a very good hypothesis. Right now I'd be willing to accept (the impact) as a probable event. ILLUSTRATION: Staff color graphic
THE BIG SPLASH
35 million years ago, a meterorite a mile in diameter splashed down
just west of what is now Cape Charles, four scientists say in a
newly published study. The 50-mile-wide crater - encompassing much
of the Bay and the Eastern Shore - would be the largest discovered
in the United States.
Source: C. Wylie Poag, U.S. Geological Survey
[This appeared on Page A1.]
[Includes map]
For copy of graphic, see microfilm
KEYWORDS: CHESAPEAKE BAY METEORITE
by CNB