[meteorite-list] Researchers Plan to Drill Under Chesapeake Bay Crater

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Jul 18 12:20:09 2005
Message-ID: <200507181619.j6IGJJM10237_at_zagami.jpl.nasa.gov>

http://www.baltimoresun.com/news/nationworld/bal-te.crater18jul18,1,4797084.story

Digging back 35 million years in crater

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

By Dennis O'Brien
Baltimore Sun
July 18, 2005

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.

Researchers hope to tap into the remnants of untouched pockets of salty
water from the original ocean, areas sealed off by clay sediments that
washed into the crater after the impact. Previous drilling projects
turned up some of the salty water, but it has never been recovered in
sufficient quantities to study it.

"This water is definitely different than anything above it or below it,"
said Mary Voytek, a USGS expert on microscopic life.

The rocks could also yield clues. The meteor strike is believed to have
heated up, smashed and sterilized subterranean rocks, creating habitats
for thermophiles and halophiles, types of bacteria that might have
evolved in the crater's superheated rocks and salty water. They could
still be living down there, experts say.

Cockell says meteorites shatter rocks in unique ways, creating tiny
fissures that make ideal habitats for rarely seen microscopic organisms.
He's optimistic that researchers will find them in the crater.

"We should keep in mind how impact events have created environments for
life; they haven't just destroyed life," Cockell said.

Such life has been found in the unlikeliest of places, including impact
craters, deep-sea thermal vents and arctic ice shelves.

There's little chance that any types of bacteria discovered will be a
threat to the health of plants, people or animals, according to Voytek,
Cockell and other experts.

Toxic micro-organisms must evolve along with hosts to develop an ability
to attack them, scientists say. The myriad bacteria found living on
volcanic slopes, deep ocean vents, polar outcrops and subterranean
habitats have shown no such capability, they say.

The ubiquitous nature of microscopic life has researchers encouraged
about what they might find in the bay crater.

"Basically, the research shows that we've found bacteria in just about
every environment where we've looked," Voytek said.
Received on Mon 18 Jul 2005 12:19:19 PM PDT