Soil is another important natural resource that supports life. Soil contains soil particles, humus and living organisms. It also contains some amount of water in the form of droplets or air in between the soil particles. The sun, water, wind and living organisms form the soil. Uneven contraction and expansion of rocks, cracks and breaks them into smaller particles of soil. Frozen water logged in the cracks of rocks, cracks and breaks the rocks into soil. Lichens growing on the surface of rocks release chemicals which powder the rocks into soil. Flowing water in rivers breaks hard rocks into soil particles. Strong winds erode rocks and carry sand particles.
Soil contains bits of decayed living organisms which is called humus. It is a major factor in deciding the soil structure because it causes the soil become more porous and allows water and air to penetrate deep underground. The topmost layer of the soil that contains humus and living organisms in addition to the soil particles is called the topsoil.