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**Soil horizons** define the layered structure of soil according to its chemical and physical characteristics. There are five main types. The **O horizon** consists of at least 20% organic matter. Based on the level of decomposition, it can be classified as sapric (highly decomposed), hemic (moderately decomposed) or fibric (minimally decomposed). The **A horizon** represents the mineral-rich uppermost layer, commonly known as topsoil. It contains decayed organic matter, giving it a darker color and fertile quality. The **B horizon** is characterized by transformation processes, including chemical changes, particularly in clay composition, and enrichment through the accumulation of materials such as clay, iron and soluble salts. The **C horizon** is composed of parent materials, such as weathered minerals that form soil particles. Minimal processes occur here, with little gain or loss of soluble materials (e.g., salts). The **R horizon** is the solid bedrock layer. ## Keywords crust pedosphere pedology soil horizon earth
