Texas A&M University (TAMU) GEOL101 Principles of Geology Exam 1 Practice Exam

Humus is defined as the decayed remains of plant and animal life, making it an essential component of soil. It forms through the decomposition of organic matter, such as fallen leaves, dead plants, and animals, which is broken down by microorganisms and other decomposers. This process converts living material into a dark, nutrient-rich substance that enhances soil fertility, water retention, and structure. The presence of humus is crucial for healthy soil ecosystems, as it contributes to the nutrient supply for plants and plays a key role in soil chemistry and biology.

Other options focus on different soil components. The solid remains of ancient organisms pertain more to fossilized materials rather than the organic matter that comprises humus. The mixture of sand and clay refers to the texture of soil, which influences drainage and aeration but does not describe humus itself. Mineral-rich layers found beneath soil relate to the parent material and subsoils, which contribute to soil nutrients but are distinct from the organic matter that humus represents.