First of all - water, and wind. The wind carries away the soil during dust storms. He chases dry soil, it blows away from the field, depriving it of its fertile layer.
The erase process of the earth's surface is called erosion. In ancient times it was very slow. With the development of human activities erosion rates increased. Has not escaped the sad fate plowed virgin Kazakh steppe. Winds of old, damp in places, blew away the top layer of soil. A similar process could prevent forest zone, but people didn't care about their landing. They wanted to bring as much land in the crop rotation, deeply cultivated land to legkostoupova wind subsoil layer. As the trees grow very slowly, much slower loaves...
Deforestation causes soil erosion in river basins. The tree roots hold the shore. Deprived of this protection, clods of earth, sand and clay fall into the river, settle to the bottom, submitted to the World ocean.
The waves of the sea eroding the rocks, washing away the rock, the river was tempted beach, sand particles are carried away by the wind, empty the once fertile arable land... So gradually changing the face of our planet.