Imagine a cross-sectional slice made down into the earth’s crust (Figure 3-1). This is called a soil profile. The mineral content of soil results from the weathering of solid bedrock or other parent material over long periods of time. The solid rock is acted on by an assortment of natural forces including temperature alternations that crack the rock, water that freezes within the cracks, and plant roots that further pry
figure 3-1. A soil profile (Delmar/Cengage Learning)
the cracks open. Then follows abrasive grinding by wind, water, and sometimes ice. Lichens and microbes may produce organic acids that react with the rock to further weaken it. While the weathering of parent material takes place over eons of geological time, it is nonetheless a simple breakdown of large pieces of rock into smaller particles.