Which of the following describes the order of soil horizons from surface downward?

The correct order for the soil horizons from the surface downward is indeed O, A, E, B, C.

The "O" horizon is the topmost layer and contains organic matter such as decomposed leaves and other plant material. It is rich in nutrients and essential for the growth of vegetation. The "A" horizon, often referred to as topsoil, is rich in minerals and organic matter. It supports most plant life and is crucial for agricultural activity.

Beneath the A horizon lies the "E" layer, which is characterized by leaching processes where minerals and nutrients are washed out, leaving a lighter colored layer often lacking in organic material. Following this is the "B" horizon, also known as subsoil, which accumulates materials leached down from above, such as minerals and nutrients. It is generally denser and may have a yellow or red color due to iron oxides and clay. Finally, the "C" horizon consists of weathered parent material, which is composed of larger rock fragments and provides the source materials for the soil above.

Understanding this sequence is important because each horizon serves distinct ecological functions and plays a role in soil formation and health.