At first, the evidence for the movement of the plates was circumstantial: the "fits" of continental coastlines, similar groups of rock and fossils in mountains facing each other across the Atlantic in South America and Africa, fossils of tropical plants and animals in what are now polar climates, and magnetic "stripes"of increasing age across the ocean floors between the continents. However, since 1976 the motion between the Pacific and North American plates has been measured directly by bouncing lasers off a satellite.

Characteristic geologic features are found at the edges of plates. Where the plates are separating on ocean floors, there are oceanic ridges. Where plates are separating on land, there are long canyons with faulted sides called rifts. Where the plates are colliding, there are either huge mountain ranges on land or incredibly deep trenches in the ocean. Volcanoes commonly occur along colliding plate boundaries.   In some places, like Southern California, the plates are neither colliding nor separating, but are simply sliding past each other. In these cases, there are great big cracks or faults (like the San Andreas in California). Unfortunately, the sliding is not smooth, but sticky and jerky. These tiny stops and starts cause huge earthquakes.