The different definitions applied to soils is indicative of the different approaches taken to them. Where farmers and engineers experience different soil challenges, soil scientists have a different view again (Johnson & Watson-Stegner 1987). Essentially, these differing views of the definition of soil are different theoretical bases for their study (Retallack 2001). Soils can be thought of as open systems in that they represent a boundary between the earth and the atmosphere where materials are transported and are changed. There are four basic types of flux: additions, subtractions, transfers, and transformations (Simonson 1978; Anderson 1988). Examples of addition can include mineral grains and leaf litter, while subtractions can include surficial erosion of minerals and of organic matter. Transfers include the movement of a material within soil profile, and transformations are the change of composition and form of the materials within a soil.