The sun is vital to all life on Earth. Evolutionary scientists have shown that solar energy played an important role in the process of 'natural origin', from the most primitive single-celled organisms dividing and developing into complex life forms. Plants need sunlight for photosynthesis or to produce sugar, and the byproduct of photosynthesis is cellular respiration, in the process releasing the oxygen we need to survive. All kinds of animals, including humans, depend on the heat of the sun to maintain their body temperature and keep them alive. Fortunately, the sun has plenty of helium to power the Earth for more than five billion years.