Soil is formed through two processes of weathering and animal humification. Weathering It
is the pulverization of rocks of breaking of rocks into fine particles.
There are three types of weathering -physical-chemical and biological.
Sun, water, wind and living organisms perform them. 1. Sun- It causes the expansion of rocks by heating. Cooling causes their contraction at different parts differently. Uneven expansion and contraction produces cracks leading to fragmentation of rocks. 2. (i) Certain rock components can pick up and lose moisture. They undergo swelling and contraction resulting in fragmentation of rocks. (ii) Frost Action is caused by water seeping in cracks that swell up and exert great pressure if it freezes due to low temperature and undergoes fragmentation. 3. Dust and fine sand carried by wind cause abrasion of the rock surface when the wind strikes the same.
4.
Lichens secrete chemicals to dissolve minerals from the rock surface and produce crevices where dust collects. Mosses grow there and cause deepening of crevices. Roots of short-lived plants widen these cracks. Roots of larger plants cause fragmentation of rocks by entering the cracks and growing in size.
Partially decomposed organic matter or humus mixes with weathered rock particles to form soil called humification. Humus
helps in formation of soil crumbs which are essential for maintaining
proper hydration and aeration of the soil.