What characteristic defines the O Horizon in conjunction with its organic material?

The O Horizon, often referred to as the organic horizon, is characterized primarily by its richness in organic material, particularly humus. This layer is generally located at the surface of the soil profile and consists of decomposed plant and animal materials, contributing significantly to soil fertility. The presence of humus enhances the soil's ability to retain moisture and provides essential nutrients for plant life, making it a crucial layer for supporting diverse vegetation.

The O Horizon is essential for a healthy ecosystem, as it not only supplies nutrients but also fosters a thriving habitat for various organisms that aid in the decomposition process and contribute to soil health. This characteristic explains why option C is the correct choice.

In contrast, other options describe features that do not accurately represent the O Horizon. For instance, the location beneath the subsoil relates more to horizons like the B or C Horizons, which primarily consist of mineral materials and typically have less organic content. Saying the O Horizon contains only inorganic elements directly contradicts its defining trait of being rich in organic matter. Lastly, characterizing the O Horizon as stony and devoid of life is incorrect, as this layer is vibrant with organic activity and crucial for supporting plant growth.