Heat radiating from Earth's core ultimately drives geological activity. Two major energy sources drive this flow of heat. First, some heat is left over from the planet's creation 4.5 billion years ago. Second, the decay of radioactive elements, especially potassium, thorium and uranium, creates a substantial amount of heat.
Heat from Earth's core moves into the mantle by radiation and conduction. In the mantle, the major mode of heat transfer changes to convection, a far more efficient mechanism for moving heat. Convection currents in Earth's mantle cause magma to rise, leading to the formation of volcanic hot spots. Heat from the mantle also drives the movement of tectonic plates. At mid-ocean ridges where plates are spreading apart, molten rock from the mantle rises and cools to form new crust. Conversely, at subduction zones, rocks from the crust sink into the mantle, where they melt into magma.