All the useful energy at the surface of the earth comes from the activity of the sun: The sun heats and feeds creatures and mankind. Each year it provides men with two hundred million tons of grain and nearly ten million tons of wood, coal, oil, natural gas, and all other fuels are stored energy from the sun. Some was collected by this season' s plants as carbon compounds. Some was stored by plants and trees ages ago. Even waterpower derives from the sun. Water turned into vapor by the sun fails as rain. It courses down the mountains and is converted to electric power. Light transmits only the energy that comes from the sun' s outer layer, and much of this energy that is directed towards the earth never arrives. About nine tenths of it is absorbed by the atmosphere of the earth. In fact, the earth itself gets only one half millionth of the sun' s entire output of radiant energy.