What layer of soil is closest to the earth's surface?

• A. B horizon
• B. A horizon
• C. C horizon
• D. Bedrock

Answer: (B)

The A horizon, also known as the topsoil, is the layer of soil closest to the earth's surface. This layer is crucial for plant growth as it is rich in organic material and nutrients. It typically contains a mixture of decomposed organic matter, minerals, and living organisms, all of which contribute to a healthy environment for root development and microbial activity.

The A horizon plays a vital role in the soil ecosystem, acting as the primary zone for seed germination and plant growth due to its fertile composition. In contrast, other layers like the B horizon, which is beneath the A horizon, consist more of minerals leached from the topsoil and may have less organic material. The C horizon is located below the B horizon and consists primarily of weathered rock such as parent material, while bedrock is the solid rock layer found below all soil layers. This context helps illustrate the A horizon's significance and relationship to the Earth's surface.