Originally Posted by
Droopy
I learned something. Thought plutonium had to be created in breeder reactors, but a quick Google search shows you're correct. It does naturally occur in very trace amounts.
All significant quantities of Pu are manmade, as you said, through custom reactor core processes.
But any conceivable element up to some reasonable atomic number (120-ish?) can be considered natural in the sense that it can probably be created by some natural process at some time or place in the universe, if not necessarily here on earth. In some cases maybe only at the big bang. Some of them decay very, very rapidly, so they certainly don't exist for long.