Subduction Goes Back-Way, Way Back!

Long in the making, the concept of plate tectonics coalesced in the 1960s. The Earth's squishy mantle churns. Above it rides immense crustal plates-some oceanic, others continental.

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These plates spread out and issue new crustal material (consider the Mid-Atlantic Ridge), slide against one another (the San Andreas Fault), head-butt (forming the Himalayas), or dive beneath each other (consider the subduction zone along the Pacific Northwest, where oceanic plates dive beneath the North American continental plate, generating earthquakes and stratovolcanoes). But how long has this process been operatin