What would happen if earth were not a convecting system

Continental drift is largely driven by mantle convection, which is what happens when the core of the earth heats the mantle, creating convection cells that carry the hot mantle material closer to the Earth's crust. The mantle material cools as it rises, until it reaches some less dense material, where it spreads out and then sinks.

Answer (d) may increase or decrease porosity through dissolution or deposition;