[meteorite-list] Chesapeake Bay Impact Crater (Part 6 of 7)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:44:15 2004
Message-ID: <200106291528.IAA28152_at_zagami.jpl.nasa.gov>

http://www.pilotonline.com/special/meteor/part6.html

NASA's hunt for ancient air
By DIANE TENNANT
The Virginian-Pilot
June 29, 2001

Part 6 of 7

A spacecraft landed in February on an asteroid.

Five years after launch, the Near-Earth Asteroid Rendezvous craft settled
gently onto the space rock and phoned home. NEAR transmitted information for
seven days from the surface of the asteroid to the surface of Earth.
Listening scientists were ecstatic.

NEAR was designed only to circle Eros, a potato-shaped rock about 21 miles
long and 196 million miles away. When the craft's yearlong mission was over,
scientists decided what the heck, why not try landing it on the asteroid?
They figured the odds of success at less than 1 percent.

It worked.

Against the same odds, another researcher is trying for his own space-rock
breakthrough: He's seeking prehistoric air in the Chesapeake Bay impact
crater.

An atmospheric scientist has to do no more than inhale deeply to find his
subject matter, but modern-day air is so common. Joel Levine has a passion
for age.

He has searched for 17th century air in lead coffins from St. Mary's City,
Md. Pinhole leaks frustrated him there. He has looked in sealed chambers in
Ethiopia. They weren't sealed tightly enough. Then David Powars called.

We have a buried impact crater, 35 million years old, Powars said. We'd like
to set up a drill rig at NASA Langley Research Center to take some core
samples in 2000. Would you be interested in collaborating?

Levine is principal investigator on Langley's proposal to fly an
``airplane'' over Mars in 2007 to examine surface features and search for
signs of life. He had been working on ways to study the impact craters that
pock the Red Planet. Here was a crater conveniently located in a
metropolitan area with good highway access. The work would be close to home,
in fact, right outside his office door.

But where, under more than a thousand feet of sediment and rock, would he
find air?

The Rosetta Stone is a piece of black basalt, a volcanic rock found in 1799
by Napoleon's troops in Egypt. Before its discovery, researchers had puzzled
over the hieroglyphs that lined walls and monuments and manuscripts. The
stone was an Egyptian-Greek dictionary of sorts, the key that helped
translate pictures into words.

``Finding a sample of old air is the Rosetta Stone of the atmosphere,''
Levine says. ``It will provide unambiguous evidence of what we, the human
race, have been doing to the atmosphere.''

Carbon dioxide is a major gas associated with global warming. Since 1958,
Levine says, carbon dioxide has increased and the ozone layer has decreased.
But that short period doesn't reveal whether the changes are caused by a
natural cycle or by man. Old air -- really old air -- could provide a base
line.

Air trapped in ice cores from the North and South poles has been dated to
400,000 years ago, but some of the data is questionable, Levine says.

``So for 95 percent of the Earth's history we have no record of what the
atmosphere was like.''

As the drill cored deeper and deeper under NASA Langley, everybody wanted a
piece of the action. Paleontologists wanted to comb portions of the sample
for fossils. Hydrologists wanted to squeeze sections for water. Geochemists
wanted bits to analyze for composition and geologists wanted the cores left
whole to look at. If he were to find air, Levine would need his own pieces
to destroy.

Levine wanted samples from the breccia, the loose clutter of rocks and
sediment that was flung into the air by the impact, then dropped into the
crater or washed back by tsunamis. And he needed them quickly, before old
air could escape the core or new air could percolate in. He and his
colleagues practiced their recovery technique in the laboratory until they
had it down to a science.

As the core came up, 4-inch segments were sliced out from varying depths.
Within two minutes of clearing the ground, they had been washed and scraped
clean of drilling mud, wrapped in aluminum foil and dropped into liquid
nitrogen for flash freezing.

Liquid nitrogen is so cold that it can nearly stop the movement of molecules
in a solid. Hypothetically, any trapped air could not leak out of the core
because its particles would be almost motionless. No gas could get out, none
could get in.

At least, in theory.

With the cores frozen harder than solid, the problem becomes releasing the
trapped air. NASA Langley has on its grounds a laboratory where various
materials are tested for strength. It has a vacuum chamber where tons of
pressure can be applied. Researchers are seeking materials 10 times stronger
than steel, and about that much lighter, so they crush things all the time.

Except dirt.

Frozen core samples, smashed in a vacuum chamber, could fling crumbs of dust
and dirt everywhere, potentially contaminating or damaging the equipment.

A special box had to be made to surround the cores inside the vacuum
chamber. The box itself then had to be tested to be sure no gas molecules
were coming from its walls to skew the test results.

Suspect results are useless.

Levine hopes to crush his samples sometime this summer.

``The first thing we have to do is look for gases that are not chemically
active,'' he says. ``Probably the most interesting gas is carbon dioxide.
We're also interested in argon, we're interested in neon, we're interested
in helium. And those four gases are very inert, chemically, so that if 35
million years ago -- and that's a big if -- if they were trapped in this
core, they would still be there.''

A shallow sea covered all of eastern Virginia then, and the meteorite landed
on the sea floor. The rock and sediment that was blasted from the crater
would have dropped back into water. Even if the four gases were trapped in
the loose breccia, they could have dissolved.

``It's a long shot, but the payoff is very high,'' Levine says. ``It would
be very derelict if we didn't try this.''

Perhaps they'd better hurry.

Reach Diane Tennant at 446-2478 or dianet_at_pilotonline.com
Received on Fri 29 Jun 2001 11:28:44 AM PDT