Soil is generally defined as the top layer of the earth's crust, formed by mineral particles, organic matter, water, air and living organisms. It is the interface between earth, air and water and hosts most of the bioshpere. As soil formation is an extremely slow process, soil can be considered essentially as a non-renewable resource. Soil provides people food, biomass and raw materials. It serves as a platform for human activities and landscape and as an archive of heritage and plays a central role as a habitat and gene pool. It stores, filters and transforms many substances, including water, nutrients and carbon. In fact, it is the biggest carbon store in the world (1,500 gigatonnes) (Soil Thematic Strategy).
Soil is consisting of layers (soil horizons) of mineral constituents of variable thickness, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and environmental processes that include weathering and erosion. (Read more : Wikipedia)