In just a few days, David Marchant and a group of Boston University students will journey up into the frigid mountains of Antarctica. It will be their home for the next few months, at the height of what passes for summer on the frozen continent.
Living in tents, under a nearly ever-present sun, the College of Arts and Sciences associate professor of earth sciences and his students will probe ice and sediment in a region known as the McMurdo Dry Valleys, as Marchant does every year. Millions of years of cold, arid conditions have left a uniquely pristine geologic record to investigate. And Marchant’s exploration of it, as evidenced by two papers he coauthored this summer, provides clues about planetary climate change, on Earth and on Mars — which has a climate similar to Antarctica’s and where such insights are key in the search for evidence of extraterrestrial life.
“You’re looking at possibly the oldest landscape on Earth, and you’re trying to derive from that landscape current information about our planet and clues for interplanetary exploration,” says Sean MacKay (GRS’13), an earth sciences doctoral student who will accompany Marchant. “It’s worth getting cold for.”
One of the recent discoveries to emerge from this remote region provides a rare window into the relatively brief period of geologic time, when a more temperate Antarctica went cold for good. The ice sheets that now cover about 98 percent of the continent started forming about 34 million years ago. But until about 14 million years ago, much of the Antarctic interior was filled with living tundra and alpine lakes. That all came to an end in a relatively sudden cooling that pushed the continent into an icebound state from which it has never emerged.
The exact timing and cause of that dramatic change is something of a mystery. But in examining the sediment of the McMurdo region recently, Marchant and fellow researchers found an important clue — they discovered fossils of mosses, insects, and crustaceans representing the last days of the Antarctic tundra. It was all contained in a thin black line of sediment that Marchant says “represents probably the greatest thermal change in Antarctica in 34 million years” — an estimated drop of about 14 degrees Fahrenheit in mean summer temperatures over a scant 200,000 years, between 14.1 and 13.9 million years ago. The speed of the change is evidenced by how well the leaves, mosses, and beetles are preserved.
“They are not decomposed or eroded; they’re freeze-dried,” Marchant says. “These things are so fresh they look like museum specimens.”
The findings, reported in the August 4, 2008, Proceedings of the National Academy of Sciences, support the theory that the advance of ice in Antarctica happened suddenly and in response to a global cooling initiated elsewhere. Marchant says that getting to the bottom of past episodes of global temperature changes resulting from natural causes allows for a better understanding of current and future changes in the planet’s climate.
“Humans are contributing to global warming,” he says. “But at the same time, climate change on Earth is almost inevitable, and the geologic record tells us that the changes can be abrupt and dramatic.”
The McMurdo Dry Valleys, for instance, went from an environment close to what exists today in Patagonia, South America’s southernmost tip, to a cold desert that’s not unlike Mars. Indeed, the similarities to Mars have led Marchant to link his work in Antarctica to investigations of the Red Planet’s climatic history, information that’s critical to the ongoing search for evidence of Martian life.
“Ultimately, NASA’s mission is to follow the water on Mars,” says Marchant, in particular those places where liquid water most recently existed. “It’s the first place you would want to look for life.”
Marchant’s understanding of how buried ice deforms the Earth’s surface in Antarctica helped NASA scientists guide the Phoenix Mars Lander to the sample of Martian ice that it scooped up this summer. In addition, Marchant and researchers from Brown University and the University of California, Santa Cruz, compared images of Martian craters with photos of the McMurdo Dry Valleys and found similar features. Writing about their resemblance in the August 25, 2008, Proceedings of the National Academy of Sciences, they concluded that Mars craters showed evidence of glaciers and meltwater that had formed gullies as recently as a few hundred thousand years ago.
Still, the flow of discovery isn’t just from Antarctica to Mars, says Marchant; after all, Mars is an entire planet of landforms shaped by the kind of climate conditions prevalent in the McMurdo Dry Valleys. “There’s a lot more to look at on Mars,” he says, particularly with the incredibly high-resolution images of the planet available from NASA. “So, by studying Mars, I’m learning more about Antarctica, and it’s actually come full circle.”
Chris Berdik can be reached at firstname.lastname@example.org.