Explain how soil is formed.

The formation of soil is a complex process. Before studying about the formation of soil let us first know about soil.

The outer layer or the uppermost layer of the earth is formed of soil. The soil is a mixture that contains minerals, organic matter, and living organisms. But broadly speaking, soil can refer to any loose sediment.

Formation of soil:

The soil is created by the process of weathering or disintegration of parent rocks by physical, chemical and biological agents. Soil formation is a slow process that takes thousands of years. Soil can be formed by three processes given below

Mechanical Weathering

This is usually observed near the surface of the earth. It is called physical weathering, as this method is influenced by physical forces such as wind, water and temperature.

Mechanical Weathering is also known as physical weathering and disaggregation. The key agent of mechanical weathering is water in solid or liquid form. Temperature changes contribute to mechanical weathering through a process known as thermal stress. The structure of the rock weakens when the temperature keeps swinging between hot and cold temperatures. When the temperature is cold, the rock contracts, and when the temperature is hot, the rock expands. This results in weakening of the rock structure.

Chemical Weathering

Chemical weathering occurs when rocks are broken down by chemical reactions. Such types of weathering can change the chemical composition of the soil.

The different chemical weathering processes are oxidation-reduction, hydrolysis, dissolution, and carbonation. In the carbonation process, the softer rocks are dissolved when water reacts with carbon dioxide resulting in the creation of carbonic acid.

Biological Weathering

The lichens growing on the rocks discharge certain chemicals that break down the rock into a fine powder and form a thin layer of soil. The mosses also develop on the rock surface and further break the rock. The roots of the trees get into the cracks of the rocks and push them to widen, thereby, breaking the rocks.

Rocks and sediments are turned into soils when they are chemically attacked by the carbonic acid which is formed due to the respiration of carbon dioxide by plant roots. The effect of living organisms on the breakdown of rock is known as biological weathering.

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