Plate tectonics is not an inevitable consequence of planet formation. Mars, for example, shows no evidence of ancient or modern plate movements, and neither does Venus. On Earth, however, plate tectonics was established early, setting in place the physical processes that sculpt Earth’s surface and, as we’ll see, maintain its environment. In consequence, Earth became more than a planet with oceans and atmosphere, mountains, and volcanoes. It became a planet capable of sustaining life.
