Dr. J. Marvin Herndon is an independent scientist who has an understandable, logical explanation for the fact that the Earth’s core has generated large quantities of heat for billions of years and for the fact that the Earth has a magnetic field that fluctuates from time to time.
The theory is called the georeactor and you can find a wealth of information about it on Dr. Herndon’s web site titled understandearth.com. If you do not feel much like reading, you can also go to episode number 48 of The Atomic Show and listen to him explain some of his ideas.
There is a pretty lively discussion going on in response to the show. Apparently it was a hit.