| Soil forms over many thousands of years from weathered rock fragments and the decaying remains of living organisms. As soil develops, it forms distinct layers, known as horizons. Each horizon has a specific color, texture, and mineral content, as seen in the vertical cross-section of soil above. The number and type of horizons in a particular soil vary, but in general the uppermost horizon of soil forms the nutrient-rich topsoil. Beneath the topsoil lies the subsoil, which contains minerals that have trickled down from the topsoil. Rock fragments reside below the subsoil, and the horizon forming the foundation of soil consists of unweathered parent rock. |
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