The O Horizon, also known as the organic horizon, is the top layer of soil primarily composed of organic matter, such as decomposed leaves, plant material, and other organic debris. This layer is rich in nutrients and plays a crucial role in supporting plant life by providing essential elements for growth. It is typically dark in color due to the high concentration of organic material. The O Horizon is found above the A Horizon, which is the topsoil layer. It is important for soil health and ecosystem functioning, as it helps retain moisture and supports a diverse range of organisms, including earthworms and microbes. This layer is vital for maintaining soil fertility and promoting biodiversity.