Identify the top layer of the soil profile.

The top layer of the soil profile is identified as the O horizon, also known as the organic layer. This layer is primarily composed of organic matter, such as decomposed leaves, plant material, and other organic materials. It plays a crucial role in soil health, providing nutrients to plants and serving as a habitat for various organisms such as bacteria, fungi, and insects. The O horizon is typically dark in color due to the accumulation of this organic matter, which helps retain moisture and improve soil structure.

In contrast, the other layers—like the A horizon, which is the topsoil primarily made up of mineral matter with some organic content, and the E horizon, known for its eluviation (the leaching of minerals), have their distinct characteristics but do not qualify as the top layer that predominantly consists of organic materials. Meanwhile, the C horizon represents the parent material from which soil is derived, lying beneath the more biologically active layers and thus not classified as a top layer either. The O horizon is essential for promoting soil fertility and biological activity at the surface of the soil profile.