Heat from the decay of radioactive elements, the previous candidate, now seems too feeble a motive force.

Polonium forms naturally after the decay of other elements, even though it is not primordial.

Beneath the Earth's crust lies the mantle which is heated by the radioactive decay of heavy elements.

It can, and is produced as a by product of the nuclear decay of other radioactive elements.

Additional heat may come from the decay of radioactive elements mixed with its iron.

Elements such as lead formed largely through the radioactive decay of heavier elements.

Much of the heat is created by decay of naturally radioactive elements.

It occurs on Earth only as the result of the radioactive decay of certain heavier elements.

That was clearly shown by the radioactive decay of certain elements.

Around 500 million years afterward, the Moon's mantle was able to be extensively melted due to the decay of radioactive elements.