the shape of the mantle does not resemble that of a cooking pot. Rather, it is a spherically shaped zone with a much larger upper boundary (Earth's surface)than lower boundary (core-mantle boundary).Furthermore, mantle convection is driven by a combination of three thermal processes:(1)heating at the bottom by heat loss from Earth's core; (2)heating from within by the decay of radioactive isotopes; and(3)cooling from the top that creates thick, cold lithospheric slabs that sink into the mantle