The A horizon, also known as topsoil, is the uppermost layer of soil. It's the richest layer in terms of organic matter and microorganisms, making it crucial for plant growth.
Topsoil is typically dark brown or black due to the presence of humus, which is decomposed organic matter. Humus contributes significantly to the soil's fertility by providing nutrients and improving its structure.
The A horizon is vital for sustaining life on Earth, as it supports the growth of plants that provide food and oxygen.
