I have been searching online for any credible information about fusion or fission occurring and contributing significantly to the Earth internal temperature. Can anyone explain this to me further? So far I have heard several media sources discussing how fusion within the Earth is a contributing factor to global warming. I had always believed that pressure was the primary cause of heat within the Earth. The http://en.wikipedia.org/wiki/Structure_of_the_Earth" [Broken] mentions nothing of fusion or fission occurring within the Earth.