Soils are loose mixtures of various components (organic matter, minerals, fragments of rocks, gases, liquids, and organisms) that forms due to the weathering of a bedrock and that sustain life (e.g. prairies, forests). In the common language, soils are referred to as earth or dirt. Soils are produced by various weathering processes that transform rocks into fine-grained material. These processes not only include chemical and mechanical weathering at the contact with water and air but also biochemical weathering caused by living organisms that attack the substratum and hold the soil together, preventing its erosion. There are several types of soils depending on the climate and bedrock where they form and the life forms that live on it. However, in general, soils show, from bottom to top:
-a rocky bedrock, which is the parent material of the soil;
– the saprolite, a layer of weathered bedrock;
– the regolith, which is a mixture of fragments of the bedrock and fine-grained soil;
– the topsoil, which is the fine-grained soil where the parent material is not recognizable anymore.

In geology, paleosoils are former soils that were buried under sedimentary or volcanic deposits and that sometimes can be found lithified as rocks.

Above: natural outcrop of a paleosol exposing the former bedrock (marble, lower left corner), a level of regolith formed from the weathering of the bedrock, and a thick reddish topsoil. On top of that, a series of Pleistocene sandstones cover the paleosol. Madonna delle Grazie, Elba (Italy).