<P> Previously, soil had been considered a product of chemical transformations of rocks, a dead substrate from which plants derive nutritious elements . Soil and bedrock were in fact equated . Dokuchaev considers the soil as a natural body having its own genesis and its own history of development, a body with complex and multiform processes taking place within it . The soil is considered as different from bedrock . The latter becomes soil under the influence of a series of soil - formation factors (climate, vegetation, country, relief and age). According to him, soil should be called the "daily" or outward horizons of rocks regardless of the type; they are changed naturally by the common effect of water, air and various kinds of living and dead organisms . </P> <P> A 1914 encyclopedic definition: "the different forms of earth on the surface of the rocks, formed by the breaking down or weathering of rocks". serves to illustrate the historic view of soil which persisted from the 19th century . Dokuchaev's late 19th century soil concept developed in the 20th century to one of soil as earthy material that has been altered by living processes . A corollary concept is that soil without a living component is simply a part of earth's outer layer . </P> <P> Further refinement of the soil concept is occurring in view of an appreciation of energy transport and transformation within soil . The term is popularly applied to the material on the surface of the Earth's moon and Mars, a usage acceptable within a portion of the scientific community . Accurate to this modern understanding of soil is Nikiforoff's 1959 definition of soil as the "excited skin of the sub aerial part of the earth's crust". </P> <P> Academically, soil scientists tend to be drawn to one of five areas of specialization: microbiology, pedology, edaphology, physics or chemistry . Yet the work specifics are very much dictated by the challenges facing our civilization's desire to sustain the land that supports it, and the distinctions between the sub-disciplines of soil science often blur in the process . Soil science professionals commonly stay current in soil chemistry, soil physics, soil microbiology, pedology, and applied soil science in related disciplines </P>

How do scientists classify the different types of soil