Regolith encompasses which part of the Earth's surface?

• A. Bedrock below the soil
• B. The atmosphere above the soil
• C. Soil horizons O, A, B, and C
• D. The living organisms in the soil

Answer: (C)

Regolith is the loose, weathered material that sits on top of bedrock. It includes the material that makes up the soil, specifically the O horizon (organic surface layer), the A horizon (topsoil), the B horizon (subsoil), and the C horizon (weathered parent material). This is why the regolith is described as encompassing these soil horizons: it represents the actual surface material derived from weathering, not the bedrock beneath or the air above. While organisms live within regolith, the regolith itself is the physical material, not the biota. If present, an E horizon would also be part of the regolith, but the horizons listed capture the essential idea.