How Does Soil Form?

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Soil forms from a parent material deposited at the surface of the Earth, such as weathered bedrock or small materials carried by blowing winds, moving glaciers and flooding rivers. The parent material transforms or changes into soil over time. The major factors that affect soil formation are parent material, climate, landscape, living organisms and time.

Soil is made of layers, which are sometimes termed horizons. When put together, these layers form a soil profile. Soil is dynamic, and it gradually looks different from its parent material as it ages. It comprises various materials, such as water, air, minerals, organisms and organic matter. These components constantly change. As time passes, some of these components are lost, and new ones are added. Some also transform into other forms, and some others move into different layers within the soil.

Parent material is the most significant factor that affects soil texture. The parent material of most soils is either sediment or solid rock. Climate, which encompasses temperature, rainfall and snow, plays an important role in breaking down rocks and determining the type of soil. Landscape significantly influences the thickness and development of soil. Steep slopes like hillsides often have thin soil because the rain washes down the soil. Animals, vegetation and fauna work together to develop soil structure. Humans have also had a considerable influence on soil formation through farming and other land activities. Lastly, soil needs plenty of time to form. Decades are needed to develop only a centimeter of soil in soft sediments.