A soil profile consists of four layers of soil called horizons. The O horizon, A horizon, B horizon and C horizon are composed of different soil materials and each goes through different processes. From decomposing organic material to unconsolidated bedrock, each soil layer is different and is important to the stability of soil and vegetation growth. Each layer gets longer as you go farther down the list, starting with a 2-inch layer of composition and ending with a 48-inch layer of bedrock.
The first layer of a soil profile is the O horizon, which is top layer of the soil. The O horizon is about 2-inches deep and consists mainly of loose leaves and organic debris. Due to the substance found on the O horizon, it is referred to as the "litter horizon." However, this layer is enriches the soil with nutrients such as nitrogen, potassium and calcium, and helps enhance the soil moisture and structure. At the bottom of this layer, all the vegetation is already destroyed by decomposition.
The A horizon is the second layer of the soil profile, extending about 10-inches deep, and is commonly known as topsoil. The A horizon is the beginning of the mineral soil, where organic material mix with inorganic material from weathering. Due to the mixture with organic material, the layer tends to be dark-colored compared to its counterparts. The importance in this layer comes from the process of eluviation, which has given it the nickname, "zone of leaching." Eluviation removes organic and inorganic material from a horizon by leaching it, which is carried downward to other layers by water.
The B horizon is the third layer of the soil profiles, extending about 30-inches deep, and is commonly known as the "zone of accumulation" and "zone of illuviation." Soluble and suspended organic material, clay, iron and aluminum are carried down from A horizon from eluviation and accumulated in B horizon. This accumulation creates a dense layer of soil and enriches the soil with calcium carbonate, turning the soil a reddish color.
The C horizon is the fourth, and final layer of a soil profile, extending about 48-inches deep. This horizon is mostly composed of weathered rock, from the soil-forming process. Due to its composition of weathered rock, the C horizon is unaffected by soil formation and does not have much internal layering of soil. The C horizon is located right above bedrock.