ICSE Class 6 Answered

Rocks are broken down into soil by the process of weathering. Weathering is disintegration and decomposition of rocks and minerals over a period of time. Weathering can be brought about by physical, chemical or biological factors.

Physical weathering: It involves wearing away of the parent rock due to physical factors such as temperature, wind and water. This causes a change in the shape and size of the rocks; however, its chemical composition remains unaltered. The parent rock gets cracked, crumbled and crushed, producing a range of materials with different sizes, from large boulders to fine particles.

Chemical weathering: Chemical processes like oxidation lead to weathering of rocks and formation of soil. For example, compounds of iron in rocks are easily oxidised to form oxides of iron, which is responsible for the red colour of the soil containing them. Limestone rocks are worn away due to chemical reactions with carbon dioxide dissolved in water.

Biological weathering: It is the continuation of physical and chemical weathering. When disintegrated products of the parent rock come in contact with living organisms, they are exposed to further physical and chemical weathering. Plant roots which penetrate the crevices and cracks in rocks grow and expand exerting pressure sideways, thereby splitting the rocks. Some roots also secrete acids which corrode the rock surface.