Soil is formed by weathering of parent rock material. This involves physical, chemical and biological processes and includes thermal weathering due to exfoliation caused by alternative expansion and contraction of rock material that happens when temperatures alternate between high and low points. Over time, surface or parent rock peel off.
Another form involves freezing and thawing, and happens in cold regions at high altitude or parent near the poles.
Due to seasonal temperature variations between winter and summer, water during summer enter crevices in liquid form. In winter it form ice/freezes. Freezing of water increases its volume exert lateral pressure which expand fissure continuing this process over time causes peeling of surfaces parent rock material.
Wind action also crodes parent rock material by abrasion of the surface.
Action of man using tools also contributes to the process of soil formation.
Chemical weathering is due to oxidation of rock material. Also by hydrolysis and hydration.
Biological weathering is caused by the activities of living organisms e.g plant root which grow into crevices and expand during secondary growth; also others like termites, which build mounds.