Humus is primarily derived from what source?

Humus is primarily derived from dead or decaying plants and animals, which is a key element in soil formation and fertility. As organic matter from these living organisms breaks down, complex compounds are formed, enriching the soil with nutrients and enhancing its structure. This process, known as humification, is vital for soil health, as humus helps retain moisture, improve aeration, and provide essential nutrients for plants.

In contrast, other options do not contribute to humus formation. Mineral deposits refer to inorganic materials that aren't involved in the formation of organic-rich soil. Commercial fertilizers may add nutrients to the soil but do not contribute to humus content, as they are synthetic and do not come from natural organic matter. Rock decomposition is a geological process that contributes to the formation of soil but does not directly lead to the creation of humus, which is specifically organic in nature.