andrew wrote:
Tim Streater wrote:

The mantle is kept hot by the radioactive decay of elements (mostly
uranium I think) which would have sunk down when the whole earth was
molten (as the iron did - hence the iron core of the planet).

You may also be thinking of the natural uranium reactor at Oklo, in
Gabon, about 2 billion years ago.


That's it.

So much of the heavier elements were formed in fusion reactions before the
earth formed?

One reason for the core to be iron is that decaying elements tend toward
iron as the most stable state I think.


Correct to my knowledge.


AJH