See Google Answers: Molten Earth core vs Solar contribution of energy. Lord Kelvin examined this issue at the beginning of the 20th century.
Elements heavier than hydrogen are mainly created by nuclear fusion in the core of stars. Elements heavier than the most stable one, iron, including radioactive elements, are mainly created in supernovas when stars of much greater mass than the sun explode.
Uranium and the other components of the Earth were present in the original nebula from which the solar system coalesced. The components of that nebula were originally blown out of supernova explosions at the death of earlier stars.
Didn’t Lord Kelvin compute the age of the earth as 80 million years based on what was known about internal temperatures and rate of cooling? And wasn’t this figure so far off because he was unaware of radioactivity, as was everyone, and its effect on internal heating of the earth?
That would seem to indicate that radioactive heating is the major cause of keeping the interior hot.
Is this still a point of scientific contention?
Yes, that’s quite correct. That was the major factor his calculations were so far off. However, I am not sure how close his calculations were otherwise regarding the amount of primordial heat.
Not that I am aware.