thumb|Loess field in Germany thumb|Surface-water-gley developed in glacial till, Northern Ireland

Soil is the naturally occurring, unconsolidated or loose covering on the Earth's surface. Soil is composed of particles of broken rock that have been altered by chemical, biological and environmental processes including weathering and erosion. Soil is different from its parent rock(s) source(s), altered by interactions between the lithosphere, hydrosphere, atmosphere, and the biosphere. It is a mixture of mineral and organic constituents that are in solid, gaseous and aqueous states. Soil particles pack loosely, forming a soil structure filled with pore spaces. These pores contain sol solution (liquid) and air (gas). Accordingly, soils are often treated as a three state system. Most soils have a density between 1 and 2 g/cm³. Soil is also known as earth: it is the substance from which our planet takes its name. Little of the soil composition of planet Earth is older than Tertiary and most no older than Pleistocene. . File:Soil profile.png|thumb|Darkened topsoil and reddish subsoil layers are typical in some regions.

Soil forming factors

Soil formation, or pedogenesis, is the combined effect of physical, chemical, biological, and anthropogenic processes on soil parent material. Soil genesis involves processes that develop layers or horizons in the soil profile. These processes involve additions, losses, transformations and translocations of material that compose the soil. Minerals derived from weathered rocks undergo changes that cause the formation of secondary minerals and other compounds that are variably soluble in water, these constitutes are moved (translocated) from one area of the soil to other areas by water and animal activity. The alteration and movement of materials within soil causes the formation of distinctive soil horizons. The weathering of bedrock produces the parent material that soils form from. An example of soil development from bare rock occurs on recent lava flows in warm regions under heavy and very frequent rainfall. In such climates, plants become established very quickly on basaltic lava, even though there is very little organic material. The plants are supported by the porous rock becoming filled with nutrient-bearing water, for example carrying dissolved bird droppings or guano. The developing plant roots, themselves or associated with mycorrhizal fungi, gradually break up the porous lava, and organic matter soon accumulates. But even before it does, the predominantly porous broken lava in which the plant roots grow can be considered a soil. How the soil "life" cycle proceeds is influenced by at least five classic soil forming factors that are dynamically intertwined in shaping the way soil is developed, they include: parent material, regional climate, topography, biotic potential and the passage of time.