Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. The Earth 's body of soil is the pedosphere, which has four important functions: it is a medium for plant growth; it is a means of water storage, supply and purification; it is a modifier of Earth 's atmosphere ; it is a habitat for organisms; all of which, in turn, modify the soil.
Soil interfaces with the lithosphere, the hydrosphere, the atmosphere, and the biosphere. The term pedolith, used commonly to refer to the soil, literally translates ground stone. Soil consists of a solid phase of minerals and organic matter (the soil matrix ), as well as a porous phase that holds gases (the soil atmosphere ) and water (the soil solution). Accordingly, soils are often treated as a three-state system of solids, liquids, and gases.
Soil is a product of the influence of climate, relief ( elevation, orientation, and slope of terrain ), organisms, and its parent materials (original minerals ) interacting over time. It continually undergoes development by way of numerous physical, chemical and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness, it is considered an ecosystem by soil ecologists.
Most soils have a dry bulk density (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm3, while the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm3.
