Over millions of years, ocean basins open and close, continents move and change shape, and mountains are pushed up and eroded away. Such dynamic processes continually reshape the surface of the Earth. The movement of rigid plates on the Earth’s surface, known as plate tectonics, is the cause of these changes. Volcanic eruptions and earthquakes are dramatic hints of the great movements that take place over the vastness of geological time.
Plate tectonics has emerged as one of the grand unifying theories of geology. It connects seemingly unrelated features and events of the planet — its continents and oceans, its mountains, its volcanoes and earthquakes — to a single global process. That process is the slow movement of plates on the Earth’s surface. These rigid plates are continually being formed, altered, and consumed. They move on the mantle below and carry the continents along with them.