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Land of the Lost
Underwater vents may hold clues to what early Earth was like
By Katherine Bourzac

In spring 2003, Alex Bradley descended hundreds of meters into the Atlantic Ocean to explore the mysterious Lost City hydrothermal fields, near the Mid-Atlantic Ridge. At Lost City, feathery limestone chimneys up to 60 meters tall stand on rocks forced up from the earth's mantle, venting gases and minerals dissolved in 90 °C seawater. At this depth, Bradley--an earth, atmospheric, and planetary sciences graduate student--could see only as far as the submarine's lights could reach. "It's like doing science in a car at night with the headlights on," he says. Using a robotic arm, he and his colleagues collected pieces of the chimneys in order to study the microbes living inside--which could, Bradley says, yield insights into what early Earth was like.

Bradley was part of the team of scientists from MIT, the University of Washington, and the Woods Hole, MA-based Woods Hole Oceanographic Institution that performed the first major study of the recently discovered Lost City vent system. He and the project's other MIT collaborator, Roger Summons--a professor of earth, atmospheric, and planetary sciences--are geobiologists. "We study the interdependence of life and earth processes in order to understand the history of the earth," explains Summons. An article presenting the expedition's results appeared in Science in March, and in it, Summons and Bradley describe the microbial communities living in the vents and how their metabolism differs from that of microbes in other vent systems.

At Lost City, life forms must compete for scarce sources of "edible" carbon. At other hydrothermal fields, the crucial element is hydrogen, which the organisms "breathe." Lost City's conditions--oxygen is scarce, but methane and hydrogen are abundant--are created by reactions between mantle rocks and seawater and make for an environment that resembles that of early Earth. Astrobiologists suspect that similar conditions may exist on Saturn's moon Titan, which has been the object of two recent expeditions. "Discovering this [vent] system at the same time as the exploration of Titan is going on" is a fortunate coincidence, Summons says.

The 2003 expedition to Lost City was only the beginning. This summer, a robotic sub will return to the vents, allowing Bradley and his colleagues to continue exploring their unique chemistry and life.