Editing Brown (section)

=== Soil ===
The thin top layer of the Earth's crust on land is largely made up of [[soil]] colored different shades of brown.<ref name="Birkeland">Birkeland, Peter W. ''Soils and Geomorphology''. 3rd edition. New York: Oxford University Press, 1999.</ref> Good soil is composed of about forty-five percent minerals, twenty-five percent water, twenty-five percent air, and five percent organic material, living and dead. Half the color of soil comes from minerals it contains; soils containing iron turn yellowish or reddish as the iron oxidizes. Manganese, nitrogen and sulfur turn brownish or blackish as they decay naturally.

Rich and fertile soils tend to be darker in color; the deeper brown color of fertile soil comes from the decomposing of the organic matter. Dead leaves and roots become black or brown as they decay. Poorer soils are usually paler brown in color, and contain less water or organic matter.
* [[Mollisols]] are the soil type found under grassland in the [[Great Plains]] of America, the [[Pampas]] in Argentina and the Russian Steppes. The soil is 60–80 centimeters deep and is rich in nutrients and organic matter.
* [[Loess]] is a type of pale yellow or buff soil, which originated as wind-blown silt. It is very fertile, but is easily eroded by wind or water.
* [[Peat]] is an accumulation of partially decayed vegetation, whose decomposition is slowed by water. Despite its dark brown color, it is infertile, but is useful as a fuel.
<gallery mode="packed" heights="150px">
File:Soil profile.png|A typical soil profile; dark-brown [[topsoil]]s, rich with organic matter, above reddish-brown lower layers
File:Mollisol.jpg|A profile of layers of [[Mollisols]], the soil type found in the [[Great Plains]] of the U.S., the [[Pampas]] in Argentina, and the Russian Steppes
File:Loess landscape china.jpg|A landscape of [[loess]] soil in [[Datong]], [[Shanxi]], China. Loess originated as windblown silt. It is very fertile but erodes easily
File:Peat-Stack in Ness, Outer Hebrides, Scotland.jpg|A stack of [[peat]] cut from the Earth in the Outer [[Hebrides]], [[Scotland]]. Peat is partially decayed vegetative matter
</gallery>