The answer is; how convection currents move in Earth’s interior
The region with the convection currents in the mantle. This region is composed of semi-solid rock with plasticity. These rocks are hot above their melting point but remain solid due to the enormous pressure in the region. The rocks in the upper mantle are cooler and denser than that at the bottom that is hotter. Therefore, the upper rocks sink slowly the bottom as the rocks in the bottom rise forming convection currents.