what-is-soil How is Soil Formed

Parent Material

Parent material is basically the earthen materials that make up the soil. It can be rocks or volcanic deposits or sediments. The parent material is largely responsible for a soils texture and sometimes a soil’s alkalinity. As this material becomes exposed to the surface they begin to erode and become altered chemically. The type of soil that forms is a result of the available rock, and which minerals are contained within. Sandstone will form coarse sandy soil. Soft shale will turn into heavy clay soils and granite bedrock produces a sandy loam.


Climate affects the degree of weathering soil will experience. More moisture from rain will speed up soil development, but to much can wash away nutrients. Dry climate soils become very fertile the first time they are irrigated, but if the evaporation rate is high salts in the soil and water will rise to the surface and reach a toxic level to plant life. Weather controls weathering factors as well, a climate that has a freezing and thawing cycle will speed up the crumbling of rocks. If a climate is warm soil organism activity will be high and chemical processes will speed up.


Topography is the surface features of a region, such as its hills, valleys, or rivers. The topography will have a direct affect on soil depth and the texture of the soil. Soils are usually deeper on flat tops and around the bottom of a hill. These areas also receive more moisture. The location of soil will also affect how climate processes impact it. Soils that get more sun exposure will be drier. The natural vegetation and growth will also affect soil composition.

Animals and plants

Animals and plants are the source of organic matter and many of the nutrients that go into soil. These are released into the soil either by physical decay after death or from animal wastes like manure.  The organic remains from the surface are worked by microorganisms into material that is incorporated into the soil. There is also the direct altering by sub-soil animals like moles and the earthworm.


Time is the encompassing factor that binds all of these materials and interactions together. Soils can go through many changes over the course of years.


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