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Clearer view under crust

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As he spreads a pair of colorful sea-floor maps across a table, Henry Dick pauses and confides that ever since graduate school, he's wanted to make some small contribution to understanding how Earth renews its crust and sculpts continents.

Now it appears Dr. Dick and his colleagues at the Woods Hole Oceanographic Institution may have contributed more than he bargained for. Drawing on results from undersea mapping and rock-dredging at opposite ends of the globe, they appear to have discovered a new class of ocean ridge, giving researchers new insights into key regions between Earth's ever-shifting tectonic plates.

The work also may answer longstanding puzzles surrounding the mechanisms that build those plates and split continents. In the long run, the results could point to potentially valuable deep-sea mineral deposits.

This represents the "biggest discovery" about the workings of ocean ridges in 20 years, says Jason Phipps Morgan, who heads the department of marine geodynamics at the GEOMAR Research Center for Marine Geosciences in Kiel, Germany.

These ridges, which crease the sea floor in oceans worldwide, are sites where material from deep within the Earth wells up to form new crust. They are said to host 90 percent of all Earth's volcanic activity. There, in the ridges and rift valleys that form plate boundaries, magma oozes from undersea volcanoes and fissures, spreading at rates that typically range from 2 to 18 centimeters (0.78 to 7 inches) every year.

At least two sections of prominent ridges beneath the Arctic and Southwestern Indian oceans were known to be among the slowest of the tectonic slowpokes. But little else was known about them, says Dick. Theories held that these ridge segments held little in the way of volcanic activity. This relegated them to the ranks of the boring. They were also hard to get to. One lies under an ocean sheathed in ice all year, while the other lies beneath seas where relentless 30-foot swells would be considered good conditions.


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