Which process dominates heat transfer in the Earth's mantle?

• A. Convection
• B. Conduction
• C. Radiation
• D. Advection

Answer: (A)

Convection dominates heat transfer in Earth's mantle. Over geological timescales, the mantle behaves as a very viscous, slow-flowing solid. Hot rock near the core becomes buoyant and tends to rise, while cooler rock near the surface sinks. This buoyancy-driven motion sets up large-scale circulation cells that transport heat from the deep interior toward the exterior much more efficiently than mere conduction could in such a thick, hot layer. Radiation plays almost no role in solids at these temperatures, since heat transfer by photons through rock is negligible. Advection is the general idea of heat being carried by moving material, but in this context the main process responsible for bulk heat transport is convection, i.e., the buoyancy-driven flow of mantle rock.