On Faculty: Geologist Marsh Prefers His Research On Ice


Emil Venere
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Homewood News and Information

     For the last four years geologist Bruce Marsh and his
graduate students have trekked to Antarctica, braving extreme
conditions and shouldering rock-laden backpacks.

     They can tell you about the strange arid cold and ultra
clear blue skies, the 24 hours of sunlight and the howling winds.
But, by far the most poignant feature is the lack of stimuli: an
absolute withdrawal from the familiar sights and sounds of
nature, said Marsh, a professor of earth and planetary sciences 
who recently returned from his latest visit to the frozen
continent.

     "When the helicopter pulls away, after all this preparation,
and grinds off into the distance, all you hear is the wind,
nothing else. There are no birds; there is nothing that you are
used to hearing, or seeing or smelling. Nothing," he said. "You
are sitting there with your equipment, piles of equipment to set
up camp. You start looking around, and it's absolutely soul
wrenching.

     "The sensations of total isolation are unbelievable."

     Marsh spent most of January in Antarctica, just as he has
done since 1993, chipping rock specimens from the bare formations
of solidified magma, or molten rock. Returning each year to the
McMurdo Sound region, a windblown place 800 miles from the South
Pole, he and his graduate students are quietly making history.

     The barren cliffs of Antarctica offer the only good view of
a process at the very heart of planetary evolution. By carefully
examining the naked remnants of ancient molten rock flows, Marsh
has discovered major flaws in conventional beliefs about the
process that formed and shaped the continents.

     His goal is to understand the physics and chemistry of
molten rock; specifically, where does it come from and how is it
brought to the surface?

     While sophisticated experiments and complex theory are
essential to Marsh's research, concrete evidence gathered in the
field is still the lynch pin that ties everything together.
Getting dirty remains a vital component of geology.

     "The rocks are the final court of appeal," said the
49-year-old geologist.

     But reaching those rocks is no Sunday drive in the country.
It's an eight-hour flight in a C-130 Hercules military transport,
equipped with skis. Antarctica is a magnet for scientists, who
travel there to study everything from atmospheric chemistry to 
subatomic particles from space. The huge aircraft, carrying
various teams of scientists, touches down on a gigantic glacier
called the Ross Ice Shelf, located about 20 miles from a
scientific outpost known as McMurdo Station.


McMurdo
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     It is summer now in Antarctica, and the research community
swells to as many as 1,000 residents.

     At McMurdo, the geologists receive all the tools they will
need, and they are schooled in survival training to learn skills
such as choosing a proper campsite and pitching a tent on frozen
ground, a sign that this will be no ordinary fieldwork. As
further proof of that, they are taught how to collect all their
bodily wastes, something that, as distasteful as it might seem,
is required by international treaty to preserve the pristine
environment. Scientists collect their waste in large urine jugs
and Teflon containers, which are brought back to the station for
incineration.

     After several days of training, Marsh and his students were
taken by helicopter to a desolate rocky desert pass where they
pitched their three small tents and set up camp. This place,
called the Dry Valleys, is a region marked by large canyons and
valleys 50 miles long.

     Antarctica, which is nearly the size of North America, is
the most severe desert on Earth, averaging an inch of
precipitation annually. Yet, 98 percent of it is covered with
snow and ice.

     It's the other 2 percent Marsh is interested in; bare ground
is a requirement for geological study.

     Despite the foreboding images conjured up by the name Dry
Valleys, the moniker is inviting to geologists: this is one of
those rare spots where no snow covers the towering cliffs and
ranging desert. 

     For two weeks the Hopkins geologists lived in the frigid,
windy desert, being ferried by helicopter to various sites,
hammering rock samples from the cliffs.

     "The terrain was incredible," said Jon Philipp, one of the
graduate students. "The whole place was incredible."

     Sometimes the work could be dangerous, like the day Marsh
and his students hunted for rock samples along the side of a
cliff 2,000 feet high. They were dropped by helicopter to the
sloping site, located a few miles from their tents.

     The next several hours proved how adventurous science can
be, as the geologists negotiated a 45-degree terrain, balancing
themselves while toting backpacks heavy with rocks.

     "It was not a fun day," Philipp said. Still, he added, the
expedition was safe and as routine as you could expect,
considering the venue.

     "I got the impression that we had a pretty tame year," he
said. "We never got stranded anywhere, which is a definite
possibility."

     Besides, the payoffs are well worth the risks. Not many
geology students have the chance to work with a scientist of
Marsh's stature in a place so rich with opportunity.

     Only the bare formations of Antarctica offer an ideal view
of what happened millions of years ago. The once-molten deposits
are commonly found on the Earth's surface, but they've either
been covered with vegetation and debris or badly weathered. For
example, Little Roundtop, the strategic hill at Gettysburg that
helped turn the tide of the Civil War, contains such solidified
magma deposits, Marsh said.


Ancient magma
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     Frozen in time throughout the spectacular Antarctic cliffs
are bands of magma, called sills, because similar material once
was used to make window and door sills. It was deposited there
175 million years ago, around the time that a supercontinent
called Gondwana broke up to form South America, Africa,
Antarctica and Australia.

     After analyzing how the largest crystals of rock are
distributed in these sills, Marsh has learned that geologists
have been profoundly wrong in their assumptions about the way
that magma behaves on its way to the Earth's surface.

     Geologists had long adhered to the idea that the magma was
injected, as if with a syringe, from its deep source to the
Earth's surface. But Marsh has found that the mushy magma is not
injected to the surface; it actually is pushed up through a
series of chambers, picking up crystals of various sizes along
the way and depositing those crystals in pools that solidify as
magma sills. Geologists have known that these crystals were a
vital component in the formation of continents. They settled to
the floors of the molten deposits, distilling and enriching the
magma and allowing it to form the material from which the
continents are eventually produced. The larger the crystals, the
more the magma was enriched.


Tiny crystals
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     But geologists have been wrong about where those pea-size
crystals came from. The conventional view was that they grew and
collected, as a sort of precipitate, in the cooling magma. But
Marsh's findings have led him to a much different explanation.

     "This model ... has been applied for a hundred years, and
it's wrong," he said. "It's very much wrong."

     Only extremely small crystals, those about the diameter of a
hair, grew in the magma. The larger crystals, which actually
spurred the creation of the continents, were transported from
great depths by the columns of molten slurry, Marsh has
concluded.

     He likens the siphoning of crystals to domestic plumbing.

     "If somebody is working on the pipes of your house and you
turn on the faucet hard, you get sand, junk," Marsh said. "If you
turn on the faucet just a little bit, you don't get any of that
junk."

     One piece of evidence supporting his theory is that some
sills contain no large crystals. All their crystals were born and
grew after the magma came to rest, and all those crystals were
too small to settle and enrich the magma enough for it to become
continental material.

     Like the slow-moving water in the domestic-plumbing analogy,
magma often does not flow with enough force to drag rocky debris
to the surface. After discovering the new detail about the origin
of the crystals, Marsh was able to use the stones as tracers, for
the first time tracking the chemical and physical path the magma
took as it flowed to the surface. 

     Some of his findings were detailed in February's issue of
Mineralogical Magazine, published by the Mineralogical Society of
Great Britain and Ireland.

     Although these findings might sound prosaic to
non-scientists, they're poetry to the ears of geologists.

     Marsh was scheduled to give a 45-minute presentation about
his research last September at the American Museum of Natural
History in New York.

     "But people kept saying, 'Tell us more, tell us more.' I
talked for four hours straight, and people loved it."

     And Marsh isn't through yet. He plans at least one more
expedition to Antarctica.