Final answer:
Soil layers form in a sequence starting with the O horizon (organic matter), followed by the A horizon (topsoil with organic and inorganic material), then the B horizon (subsoil with fine material), and finally the C horizon (soil base with parent material) above the bedrock.
Step-by-step explanation:
The sequence that accurately explains the formation of soil is as follows: The O horizon contains freshly decomposing organic matter at the top and decomposed vegetation at the base, enriching the soil with nutrients.
The A horizon, or topsoil, has a mix of organic material with inorganic products of weathering, making it darkly colored and fertile, and often several inches deep. Below this is the B horizon, or subsoil, where fine material from above accumulates. This dense layer may contain nodules or layers of minerals like calcium carbonate. The C horizon is the soil base, composed of parent material and broken down organic and inorganic matter, lying just above the bedrock, which has little or no weathered rock.
Leaching can occur in any of these layers but is most often associated with the E horizon (not mentioned in the sequence provided but typically present between the A and B horizons), which is not a primary feature of the overall soil profile described here.