Humus is the organic component of the soil. Humus is formed by the decomposing action of soil microorganisms (e.g., bacteria and fungi), which break down animal and vegetable material into elements that can be used by growing plants. The characteristics of humus: It binds the soil together, and prevent soil erosion. Humus content affects the colour, texture, and structure of the soil. Soil with rich humus tends to be dark with a loamy texture.

Soil formation occurs over a period of thousands of years. It is a result of the continuous breaking down of rocks into smaller pieces by the forces of nature. The process by which rocks on the Earth's surface disintegrate due to the action of natural forces such as strong winds, flowing water, ice, roots of plants and so on is called weathering. Extreme differences in temperatures cause rocks to expand when the weather is hot and contract when it is very cold. Alternate expansion and contraction weakens the rocks, causing them to disintegrate into small pieces. In cold weather, water flowing through the cracks of rocks freeze and expand to form ice. The ice also causes rocks to crack and break down.