The primary heat source for convection currents in the mantle is not the sun, but rather the decay of radioactive elements within the Earth's interior. The mantle is the layer of the Earth beneath the crust and above the outer core. It is made up of solid rock that is very hot and under immense pressure. The heat from radioactive decay causes the rock in the mantle to become less dense and rise, while cooler, denser rock sinks. This creates convection currents that move the rock around and transport heat from the Earth's interior to the surface. The sun does provide some heat to the Earth's surface, but it is not the main heat source for convection currents in the mantle.