...Soil is a natural body consisting of layers (soil horizons) of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics.Birkeland, Peter W. Soils and Geomorphology, 3rd Edition. New York: Oxford University Press, 1999. It is composed of particles of broken rock that have been altered by chemical and environmental processes that include weathering and erosion. Soil differs from its parent rock due to 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.Voroney, R. P., 2006. The Soil Habitat in Soil Microbiology, Ecology and Biochemistry, Eldor A. Paul ed. ISBN=0125468075 James A. Danoff-Burg, Columbia University The Terrestrial Influence: Geology and Soils Soil particles pack loosely, forming a soil structure filled with pore spaces. These pores contain soil solution (liquid) and air (gas).Taylor, S. A., and G. L. Ashcroft. 1972. Physical Edaphology Accordingly, soils are often treated as a three state system.McCarty, David. 1982. Essentials of Soil Mechanics and Foundations Most soils have a density between 1 and 2 g/cm³. Pedosphere.com 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 the Tertiary and most no older than the Pleistocene. . In engineering, soil is referred to as regolith, or loose rock material.thumb|Darkened topsoil and reddish subsoil horizons|layers are typical in some regions.] Read full entry

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