On Faculty: Geologist Marsh Prefers His Research On Ice Emil Venere ----------------------------------- 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 ----------------------------------------------------------------- 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 ----------------------------------------------------------------- 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 ----------------------------------------------------------------- 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.
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