EARTH'S FEATURES OVER TIME

A central idea in geology is that the earth is constantly changing. Wind, water, ice, volcanism, and tectonic forces act as agents of this change. External processes (erosion) tend to wear down the earth's surface, whereas internal processes (volcanism) generally build up the earth's surface.Geological changes occur due to powerful forcess based directly or indirectly on energy from the sun and on gravity. Earthquakes and volcanoes occur along certain belts called plates. These plates move constantly. Plate motion produces mountains, the ocean's ridges and trenches.