Explain the role of the sun in the formation of soil.


Explain the role of the sun in the formation of soil.


Paedogenesis: It is the process of formation of soil from rocky crust of earth. Paedogenesis occurs in two stages, weathering and humification.

1. Weathering

It is the process of breaking down of rock present on the surface of earth into fine particles. Weathering is caused by three types of processes - physical, chemical and biological. Physical weathering is pulverisation of rocky matter caused by physical phenomena like atmospheric changes (heating, cooling, wetting-drying, frost action) and mechanical forces (abrasion by rain and hail, rolling stones carried by water, wave action, sand blast by wind). Chemical weathering is pulverisation of rocks by chemical action in wet weather like hydration, oxidation, reduction, carbonation and solubilisation. Biological weathering is the breaking down of rocks by the action of living organisms.


It heats up the rocks during the day. Heating causes the rocks to expand. During night, the rocks cool and contract. Different parts of a rock expand and contract at different rates resulting in its cracking and breaking up into smaller pieces or fragments.

2. Humification

It is the addition of partially decomposed organic matter or humus to the weathered rock particles to form soil. Humus binds the finely ground rock particles into aggregates called crumbs. Crumb formation is needed for both hydration and aeration of soil.

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