Understanding the Geology of the World
Created from intense meteorite bombardment during the formation of the earth billions of years ago and added to by continuing radioactive decay within the earth's interior, the earth's internal heat is an extremely important source of energy on this planet. This heat, and the slow "soup-in-pot" convection that it causes within the earth, in turn cause features that we can observe and study on the earth's surface: molten material erupts from volcanoes, earthquakes shake the ground, continents move, and entire ocean basins appear and then disappear.
Over time, these phenomena have totally changed the appearance of the earth: the continents have grown and changed shape along the way. Even though most geological change occurs too slowly for humans to observe directly, the vastness of timebillions of yearsover which the earth has existed allows enormous amounts of change to occur.