First National Soil Survey, U.S. Bureau of Soils, 1909. You may download lecture visual materials as a PDF file 1. Soils From our previous discussion, we know that all our elements, with the exception of hydrogen and helium, came from the dying throes of large stars. Furthermore, we know that the amino acids needed to build animal proteins come from autotrophic plant life.
Plants synthesize amino acids from the combination of sunlight, water and soils.
Figure 1 Layers of Horizons of a typical soil profile Soil is therefore of critical importance to life. We first define soil as a dynamic natural body capable of supporting a vegetative cover. Soil is composed primarily of weathered materials, along with water, oxygen and organic materials. Luckily for us, soil covers most of the land surface with a fragile, thin mantle. Soil and agricultural scientists have identified a huge number of different soil types.