Erosion is the displacement of solids (earth, mud, rock and so on) through natural causes. There are several causes of erosion, the most common being water or wind movements. As the material is removed, it is carried to other locations and deposited as silt. This deposition is called sedimentation, and most of the silt created by erosion ends up in sediment layers.
Erosion is in itself a naturally occurring process, but it is in many cases increased by human activities. Some of those include deforestation, overgrazing and trail-building. Likewise has humans sought to limit erosion by for example terrace-building and tree planting.