Which of the following describes the O horizon in soil?

The O horizon is a distinct layer within the soil profile that is primarily composed of organic materials, such as decomposing leaves, plant debris, and other organic matter. This horizon is crucial for soil health, as it contributes to soil fertility and provides essential nutrients for plant growth. The organic materials found in the O horizon play a vital role in the ecosystem by supporting a diversity of life, influencing moisture retention, and enhancing soil structure.

In contrast, the other descriptions do not accurately represent the O horizon. For instance, the claim that the O horizon is rich in minerals pertains more to the A horizon or B horizon, where weathering and mineral accumulation occur. The idea that it consists mainly of weathered rock is descriptive of the C horizon, which indicates the parent material that has not been significantly altered by soil-forming processes. Lastly, the presence of clay and silt is characteristic of finer textured soils, often found in the B horizon. In summary, the defining trait of the O horizon is its organic composition, setting it apart from the other soil layers.