Final answer:
In soil profiles, the O horizon contains decomposed organic matter, the A horizon (topsoil) contains a nutrient-rich mixture of organic material and minerals, the B horizon (subsoil) consists of accumulated fine material with leached minerals, and the C horizon is made up of weathered parent material.
Step-by-step explanation:
Soil profiles consist of multiple layers, known as horizons. Each horizon has distinct features and serves different functions in the ecosystem. The uppermost layer is the O horizon, which contains organic matter such as decomposed leaves and is vital for nutrient cycling. This layer is typically found beneath a layer of leaf litter and un-decomposed organic material at the surface.
The next layer is the A horizon, which is also known as the topsoil; it has a mixture of organic matter and minerals, providing essential nutrients for plant growth. This layer is darker due to the organic material and is where most root activity occurs.
Below the A horizon lies the B horizon or subsoil. It accumulates materials like clay, leached from the upper horizons. This layer is denser and often contains minerals that have been transported from the A horizon.
The C horizon, or soil base, lies beneath the B horizon and comprises weathered parent material. Here, the soil begins to form as the rock breaks down physically and chemically.
In summary, the O horizon mainly comprises organic matter, the A horizon is rich in nutrients forming the topsoil, the B horizon is the dense subsoil layer enriched by materials leached from above, and the C horizon is composed of weathered parent material forming the soil base.