Weathering is the breakdown of rocks on the earth's surface due to natural forces. Actions of sunlight, water, ice, wind and plants, break huge pieces of rocks to form soil. Microorganisms also contribute to the formation of soil by decomposing the dead remains of plants and animals, thus forming humus.

Humus is the organic component of soil, formed by the decomposition of vegetable or animal matter. It enriches the soil by retaining water and nutrients. Topsoil contains a lot of humus.

The subsoil is the soil that lies under the layer of topsoil and is comparatively harder and more compact. This is present in B-Horizon. It is not suitable for plant growth as it contains very little organic matter. It contains more sand and some stones.