[meteorite-list] Chesapeake Bay Impact Crater (Part 7 of 7)
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:43:28 2004
By DIANE TENNANT
June 30, 2001
Part 7 of 7
A small red or brown dwarf star may travel an elongated path that brings it
around our sun about every 26 million years. This star would travel a path
that takes it 2.4 light years away -- far, far beyond Pluto -- then back to
within half a light year, still a little past Pluto.
The orbit would take it through the Oort cloud, a region outside our solar
system filled with rocks and icy balls, thought to give birth to comets. As
it passes through, the star's gravitational pull might bump comets loose,
setting them on a collision course with Earth.
Although this star never has been observed, the outer planets sometimes
stray from their predicted orbits, as though tugged by an invisible string.
And spurts of comet or meteorite impacts over millions of years have
coincided with Nemesis' closest approach.
Early reptiles and marine life were wiped out 198 million years ago. The
dinosaurs died around 65 million years ago. The Chesapeake Bay crater was
formed about 35 million years ago.
If Nemesis is out there, we're due.
''How deep are you?'' David Powars shouts over the noise of the
truck-mounted drill rig.
``Six-'' the driller pauses for mental arithmetic. ``Ninety-five.''
``Ooooooooh!'' Powars exclaims, rubbing his hands together, and not just for
warmth. The core hole is 695 feet deep. The top of the tortured rubble that
fills the crater -- jagged granite, shocked quartz, plasticized clay -- is
nearly in reach.
``One of my greatest joys is watching that come up,'' Powars exclaims,
waving his arms and rising on his toes for emphasis. He bounds away as
though the drill has just penetrated a high-voltage electrical line.
On the first day of spring, March 21, 2001, the U.S. Geological Survey
begins its second year of crater research, drilling a core hole into a
commuter parking lot on Va. 14 in Mathews County. A second core hole is now
being drilled in the county, this one on the edge of the Bay in Shadow.
Powars looks around for a razor blade, settles for a 12-inch knife, trims a
sliver of mud off a core sample, misplaces his glasses, shoots a whole roll
of film, reloads his camera, shoots another roll and inhales. Scott Bruce
looks up from his logbooks and field notes, thoughtfully watches the
performance for a minute, then silently rescues the glasses from boot-soled
They have worked together for 15 years. The scene is repeated endlessly, but
it never gets old: Another core comes out of the hole, slimy with drilling
mud, is cradled in plastic tubing, handled with surgical care to avoid
contamination with younger dirt. It is washed, measured, scratched,
microscoped, labeled, photographed, sliced and stored.
Every sample makes its case for what Powars humbly calls the greatest
catastrophe that ever occurred on the East Coast since the origin of the
Discover magazine, in October, listed 20 ways that the Earth might end.
Topping the list was collision with a giant comet, asteroid or meteor.
``I think, eventually, just because it's a matter of time, there will be a
large massive object that will hit the earth,'' says Joel Levine,
atmospheric scientist at NASA's Langley Research Center.
USGS scientist C. Wylie Poag estimates that one house-sized object per month
disintegrates in Earth's upper atmosphere. Estimates are that between one
and a dozen marble-sized or smaller meteorites land in Virginia each year,
where they masquerade as ordinary rocks.
Others are large enough to attract attention. In 1991, '92 and '94,
brilliant fireballs over Hampton Roads prompted many frantic calls to police
about burning airliners. In 1972, a large fireball was filmed skimming the
western United States and Canada. It rose into the air until it disappeared,
presumably escaping Earth's gravity.
Others don't. Something exploded in the air above Tunguska, Siberia, in
1908, leaving trees flattened for several miles around. In January 2000, a
220-ton meteorite shattered over British Columbia, splattering a frozen lake
No one was injured.
But large craters on Earth, on the moon, on Mars and on asteroids prove that
impacts do occur, and some folks are starting to worry. About five years
ago, NASA started searching the skies for objects like asteroids and comets
that could threaten Earth, Levine says. Astronomers find them, catalog them
and assess the risk of collision. By early May, 307 potentially hazardous
asteroids had been identified, but none poses significant danger.
``I think that if anything is coming toward us that's big enough to cause
damage, we'll know about it several days in advance,'' he says.
Although a few days sounds like precious short notice, that may be all
that's needed for a well-prepared world to detonate a nuclear warhead close
enough to the invader to nudge it away from Earth without shattering it into
millions of pummeling meteorites.
If we see it coming.
``Well, it depends on how big it is, it depends on what direction it's
coming from,'' Levine says. ``If, for example, it's coming from the sun's
direction, you won't be able to detect it because the sun is too bright. But
if it came from the opposite direction, you could see it at night.''
If the Chesapeake Bay meteorite hit today, in exactly the same location, it
would destroy most of the major East Coast cities, says Poag in his book,
The millions of people who live there would be dead in a matter of minutes.
Assuming that doesn't happen in the next three years, research will continue
on the existing crater.
It's important, Levine says, to understand the effect on the Earth as a
``The atmosphere affects the ocean, the ocean affects the atmosphere, the
atmosphere is affected by land, life is affected by the atmosphere, the
ocean is affected by land -- they're all interconnected,'' he says.
The meteorite, or comet, or asteroid seared its path through the sea with
heat and light born of friction. Faster than instantly, seawater exploded
Sunlight broke apart the airborne water molecules, creating hydrogen atoms
and hydroxyl radicals, which combine one oxygen and one hydrogen atom. It
converted salt -- sodium chloride -- into chlorine. All are efficient
destroyers of ozone.
In a matter of minutes or days, a hole had opened in Earth's protective
ozone layer, larger than the one over Antarctica today. No one knows how
long it lasted.
``I think this will be some world-class science coming out of this, and
world-class science is going to impact not only the people in this community
but the people in the entire world,'' Levine says. ``We're going to learn
more about impact phenomena from this crater than from any other crater.''
Powars -- a biologist in college, a geologist in career -- has been studying
physics of late.
``I'm finding out that when the thing hits, all of a sudden it can start
moving the target rocks as fast as the impactor was traveling,'' he says,
his right hand smacking the palm of his left. ``The rock it hits actually
starts traveling that fast or faster, that's how they can escape. When you
get these rocks that you find on our planet from Mars or from the moon, they
actually have escape velocity. It hits and then it gets blown out of the
crater and can fly right out of gravity. Zoop! I'm getting more and more
impressed as I get into the mechanics of stuff.
``Now, instead of just describing that we had a hole, we're starting to get
into the placements, the timing and the mechanics. We're at the beginning of
He has been busy this spring, giving talks at the Lunar and Planetary
Conference, the Geological Society of America, the Carnegie Institute of
Washington, the Virginia Air and Space Museum. The seismic reflections from
the NASA core hole have just been processed and are ready for him to study.
The Mathews cores are coming up. The work must be repeated in different
locations. Time is in short supply.
He takes a minute of it to look over his paperwork on the Kiptopeke core
hole. ``It was pretty cool that the story really built on (John)
Cederstrom's stuff,'' he says.
``They'd talked him out of his interpretations in the '50s and got him to
rescind on them: No, it wasn't so deep and this is contaminated and you
can't use this information. That was one of the main arguments against me,
that I was using data that you couldn't count on. It was not poor quality
data. Cederstrom was talked out of it, but I kept saying no, I have a trend
Cederstrom lost his job because of it and was rehired. Powars lost his job,
too, and was rehired as a temporary. That job is about to end, and he may
soon be out of work again. He is not bitter.
``Oh, yeah, it was worth it,'' he says. ``It was worth it because I like
doing puzzles as much as anything, and this is a puzzle still unfolding.
``Who cares who thought what when, to be honest. I care about what are we
going to do with it now, and what are we going to do tomorrow with it? I'd
rather spend the little bit of time I have on the planet working another
So he stands in the mud on a cold spring morning in a parking lot near
Mathews, watching, waiting, hoping for the drill bit to penetrate the scar
of an ancient crater, a ravaged pit where death appeared 35 million years
ago, on the day the sky fell and the heavens rained fire and brimstone.
Reach Diane Tennant at 446-2478 or dianet_at_pilotonline.com
Received on Sun 01 Jul 2001 04:35:59 PM PDT