Radioactive decay of granite and other rocks in the Earth's interior provides sufficient energyto keep the interior molten, to heat lava and to provide warmth to hot springs. This is due tothe average release of about 0.03J per kilogram of granite each year. How many years are required for a "chunk" of thermally insulated granite to increase in temperature by 400°C.The specific heat capacity of granite is 800J/Kg°C.