Overview

It took nearly a century for scientists to accept the idea that continents were not forever fixed in their places, but had, in fact, slowly drifted to their current locations. In the 1960s plate tectonics, a further refinement of this concept bolstered by irrefutable geologic proof, burst into widespread acceptance in less than a decade.

Plate tectonic theory holds that continents ride atop thin plates of crust that are constantly moving across the face of the Earth. These plates break apart at midocean ridges, such as the mid-Atlantic Ridge; when they come together, one plate dives beneath the other to be recycled into the mantle—a process called subduction. These subduction zones, appearing as deep-sea trenches, are the sites of most of the world's earthquakes. As the plates descend...