Living organisms require energy to stay alive, such as the energy humans get from food and oxygen. Human civilization requires energy to function, which it gets from energy resources such as fossil fuels, nuclear fuel, or renewable energy. The processes of Earth's climate and eco- system are driven by the radiant energy Earth receives from the Sun and the geothermal energy contained within the earth. Our Sun transforms nuclear potential energy to other forms of energy; its total mass does not decrease due to that itself (since it still contains the same total energy even in different forms) but its mass does decrease when the energy escapes out to its surroundings, largely as radiant energy.