Describe how erosion wears down Earth's surface.

Erosion is a natural process which is usually made by rock and soil being loosened from the earth's surface at one location and moved to another. Erosion changes the landscape by wearing down mountains, filling in valleys, and making rivers appear and disappear. It is usually a slow and gradual process that occurs over thousands or millions of years. But erosion can be speeded up by such human activities as farming and mining. Erosion begins with a process called weathering; in this process, environmental factors break rock and soil into smaller pieces, and loosen them from the earth's surface.