Final answer:
OSHA recognizes four soil types that correspond to soil horizons: O (topsoil), A, B (subsoil), and C (soil base). These layers are integral to plant life and ecosystem function.
Step-by-step explanation:
The four different soil types that OSHA recognizes are based on their texture and composition. They are categorized into the soil horizons O, A, B, and C. The topsoil, related to plant growth and microbial processes, is referred to as the O horizon. It has freshly decomposing organic matter, known as humus, at the surface. The A horizon is the next layer and consists of a mixture of organic material with inorganic products of weathering. The B horizon, which accumulates mostly fine material, is considered the subsoil. The C horizon is the soil base and includes the parent material, plus the organic and inorganic material that has broken down to form what we recognize as soil. Each of these layers possesses distinctive physical properties and plays a critical role in supporting plant life and ecosystem functioning.