Prior to the late 1960s, most geologists held the view that
the ocean basins and continents had fixed geographic
positions and were of great antiquity. Researchers came
to realize that Earth’s continents are not static; instead,
they gradually migrate across the globe. Because of these
movements, blocks of continental material collide, deforming
the intervening crust, thereby creating Earth’s great
mountain chains (Figure 2.1). Furthermore, landmasses
occasionally split apart. As continental blocks separate, a
new ocean basin emerges between them. Meanwhile, other
portions of the seafloor plunge into the mantle. In short, a
dramatically different model of Earth’s tectonic processes
emerged. Tectonic processes are processes that deform