CBSE Class 9 Answered

Over long periods of time, the rocks at or near the surface of the earth are broken down by various physical, chemical and some biological processes. The end product of this breaking down, is the fine particles of soil. The heating up of the rocks during the day and their subsequent cooling down at night results in the formation of cracks and ultimately the huge rocks break up into smaller peices. Water also helps in the formation of soil.  Water gets into the cracks in the rocks and when it later freezes it causes the cracks to widen. Also, fast flowing water often carries big and small particles of rock down stream which rub against other rocks resulting in the rocks to wear down into smaller particles. Wind and living organisms also influence the formation of soil.