The degree to which biological processes, chiefly involving vegetation and microorganisms, contribute to soil formation is dependent on the temperature and available moisture. Plants also control the moisture content of the soil by transpiring water and serve to protect soils from erosion. These biological processes are, in turn, influenced by climate and by parent material from which the soil forms, since these control the development of vegetation which, in turn, may permit animals to flourish. In physical weathering , rocks are broken down to smaller pieces by various natural agencies, the importance the importance of which will depend on the type of rock being weathered and the climate under which weathering occurs. Wind, rain, frost action, and the differential expansion and contraction during rapid heating and cooling all contribute to the breaking down of rocks.
Most rocks already contain planes of weakness or planes along which fracturing has occurred.
The release of the confining pressure of overlying rocks, when material originally formed at depth is exposed at the surface, causes expansion, fracturing, and the formation of joints. Joint planes are also formed when an igneous rock cools. In the broad temperature belts, frost wedging is probably the most important physical weathering agent. When water, trapped in fractures or pore space in rocks at the surface, freezes, its volume increases by about 9 percent. Although such maximum forces do not occur, because ice itself is not strong enough to seal water into a rock crack, frost wedging does produce stresses capable of disintegrating the hardest rocks.