Which horizon is described as partially altered parent material?

• A. O Horizon
• B. A Horizon
• C. B Horizon
• D. C Horizon

Answer: (D)

Partially altered parent material describes a horizon where the original rock is beginning to weather, but the soil has not developed the features seen in the surface horizons. This is the horizon that sits below the surface layers and above the bedrock, showing chemical and physical changes in the parent material while still containing recognizable chunks of the original rock. It lacks the organic-rich, mixed surface qualities of the topsoil and the obvious accumulation processes seen in the subsoil, so it’s considered only partly weathered. In most soil profiles, this is the layer known as the C horizon.