Convection cells in the earth's mantle require a source of energy. what is that source of energy?

Convection is a type of heat transfer that is driven by the flow of liquid, or by a solid or weak material. These convection cells that flows in a circular direction are caused by the initial heating of earth's core. Earth is hot due to the original formation, and what keeps the heat circulating is radioactive decay. As unstable elements decay, they release energy and heat, which promotes convection cells in earth's mantle [hope this helps].