Geothermal energy is obtained by using the heat stored in the Earth’s interior to heat up water, which is brought back to the surface as steam. The steam is used to drive an electric generator. What is the source of heat for geothermal energy? A) Earth's internal heat is thermal energy generated from underground geysers. B) Earth's internal heat is thermal energy generated from molten rock under great pressure. C) Earth's internal heat is thermal energy generated from radioactive decay and molten rock. D) Earth's internal heat is thermal energy generated from radioactive decay and continual heat loss from Earth's formation.