[schiffern]

True, tidal isn't nuclear. Basically everything else is.

>Some is _also_ the result of radioactive decay, though I don't have the precise breakdown.

Neither do I, but here's my logic: if there were no nuclear power in the center of Earth, Lord Kelvin tells us it would solidify in only ~40 million years[1]. The Earth being 100 times older, the amount of residual heat left today must be insignificant.

Stellar magnetic fields come from the convective mantle, which is nuclear powered. Not sure about planetary magnetic fields, but the above analysis suggests nuclear as well. Collapsed stars will be heated by gravitational potential, but we don't see a lot of those 'round these parts.

[1] https://en.wikipedia.org/wiki/William_Thomson,_1st_Baron_Kel...

[dredmorbius]

My point wasn't that the vast, vast majority of energy available to humans on Earth isn't ultimately nuclear in origin. Just that there are energy potentials in the Universe which aren't nuclear in origin. If you trace back the formation of the Solar System itself, as a generation 3-4 system, even the gravitational potential represented in it originates from nuclear reactions.

The Big Bang (background microwave radiation) and Dark Energy would also come to mind as non-nuclear energy systems.

Not of much practical use to us on Earth, however.