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Using Rocks as Time Machines

Clare M. Williams a graduate student in the MIT/WHOI Joint Program, examines a rock collected from the seafloor to analyze its magnetic properties. Magnetism lets her unravel the patterns of lava flows to learn how ocean crust seafloor periodically, at different spots, to build up crust,” said builds up over time. “We know that lava flows come out onto the Williams. “You can tell an old flow [which has a lower-intensity magnetic signal] from a new flow.” (Photo by Tom Kleindinst, Woods Hole Oceanographic Institution)