GEOLOGY

Detailed explanation-1: -It contains more organic material than the subsoil and so it is darker in color. Humus is the decayed remains of the plants and animals, which breaks down in thesoil by the microbes. Therefore, this happens more in the topsoil, than in any other soil layer. Thus, the top layer of soil has more humus than other layers.

Detailed explanation-2: -The uppermost layer is called topsoil and this layer contains humus, plant roots, and living creatures. The more humus found in topsoil, the more nutrient rich the topsoil and the better the conditions for growing plants.

Detailed explanation-3: -Humus is present in the topmost layer of soil.

Detailed explanation-4: -Topsoil is the uppermost region of the soil profile. It contains Humus(partially decomposed and decayed organic matter), living organisms, and embedded shoots and roots of small plants.