This is a question that you have answered for yourself every time that you have been sunbathing. Almost all of the Earth’s heat, and this means its energy, must come from the Sun. In addition to this the interior of the Earth has retained much of the heat which was generated as the formation of the Earth. This internal heat came from energy released as the Earth contracted as well as from heat given off by the decay of certain types of radioactive materials. No plants would grow without the Sun, and therefore, no animals and no man. Without the Sun, our planet would be a frozen, barren waste.