At the top of the world in the late summer of 2001, the U.S. Coast Guard's icebreaker Healy carved a slow path through the ice-covered Arctic Ocean. On board, marine geologist Henry Dick sent dredge after dredge through the ice to the seafloor, searching for telltale rocks that would help shed light on how Earth's crust forms. "People said, 'You'll never get a single rock off the seafloor,'" Dick says. "They said, 'You can't dredge in the ice.'" But in fact, Dick's team collected more than 200 rocks—many of which turned out to be pieces of Earth's mantle.
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