Soil particles pack loosely, forming a soil [[structure]] filled with pore spaces. These pores contain soil [http://en.wikipedia.org/wiki/Solution 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 the [http://en.wikipedia.org/wiki/Tertiary Tertiary] and most no older than the [http://en.wikipedia.org/wiki/Pleistocene Pleistocene]. In engineering, soil is referred to as regolith, or loose rock [[material]]. | Soil particles pack loosely, forming a soil [[structure]] filled with pore spaces. These pores contain soil [http://en.wikipedia.org/wiki/Solution 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 the [http://en.wikipedia.org/wiki/Tertiary Tertiary] and most no older than the [http://en.wikipedia.org/wiki/Pleistocene Pleistocene]. In engineering, soil is referred to as regolith, or loose rock [[material]]. |