Radioactive decay of granite ---> How many years does it take? 1. The problem statement, all variables and given/known data Radioactive decay of granite and other rocks in the Earth's interior provides sufficient energy to keep the interior molten, to heat lava and to provide warmth to hot springs. This is due to the 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. 2. Relevant equations It looks like we've been given the change in temperature and the specific heat capacity for granite so it is likely that we will need to be using the equation: Q=mcΔT 3. The attempt at a solution Q=m(800)(400) Not sure where to get the mass or value for Q though. So far, we have two unknowns. Any help would be appreciated!