Soil

Soil, uppermost surface layer of the earth, in which plants grow and on which, directly or indirectly, all life on earth depends. Soil consists, in the uppermost layers, of organic material mixed with inorganic matter resultant from weathering. Soil depth (where soil exists) may reach to many meters. Between the soil and the bedrock is a layer called the subsoil. Mature (or zonal) soil may be described in terms of 4 soil horizons. The uppermost layer, containing organic components, is a continuous stream to which is added an “active” component produced by bursts of activity on the sun's surface.