First man-made fission reactor, yes. But Nature beat us by around 1.7 billion years. Fusion reactors predate even that. https://en.m.wikipedia.org/wiki/Natur

First man-made fission reactor, yes. But Nature beat us by around 1.7 billion years. Fusion reactors predate even that. https://en.m.wikipedia.org/wiki/Natural_nuclear_fission_reactor https://en.m.wikipedia.org/wiki/Natural_nuclear_fission_reac...