cooled off already? I can see where there is decent insulation and layers that can function as different media, but it seems to my lay, ignorant mind like billions of years would have led to much lower than current temperatures. What am I missing? (since my lay estimation is clearly wrong)
Orbital Gravitational Heating imo, see New Scientist Are Venus and Earth in a long-distance relationship?. It would require a change in laws of gravity and matter btw.
A good explanation of heat sources in the Earth.Please Register or Log in to view the hidden image! http://www.mantleplumes.org/Energetics.html
. i think the heat source, is the gravity, also the movement of the planet, also the moon around it, also all the other planets in the solar system, i think this realtions between parts and composentsof space, like gravity, ( spining, moving, etc etc etc...) have to do something with it; i think also it have something to do, with the sun, it give us energy, what about the solar radiations that go to the poles cause of the magnetic field, just a guess
Perhaps what you're missing is the fact that the earth has cooled down colossally during those billions of years. The whole planet was originally liquid! I can't find any information on what its temperature was four and a half billion years ago, but I'm sure its creamy rich center is considerably cooler than it was then, even though it's still at 9,000 degrees Fahrenheit (5,000C). In a couple of billion years the sun will expand and start making the earth hotter again. I wonder if anyone can calculate whether the core will have solidified by then. The surface will heat up to the point that water can no longer exist in a liquid state and life will become impossible. I don't think air conditioning will work with such a high external temperature. But even if a few enclaves of humans survive in bunkers, as the sun continues to expand the earth will be swallowed up in it and return to a gaseous state. Finally the sun will cool and contract in death to a red dwarf. I think the timeline for that is about six billion years. I don't know if it will have grabbed all the outer planets too, but at least as far out as Mars. We need to find a way off of this lonely little rock. That is the reason we have to have a space program. Sure, that's a long time off. So was Y2K and nobody (except me and a handful of others) worried about that until the last minute either.
There is evidence to support the mantle (at least) being substantially hotter than it is now - for example Archaean and Neoproterozoic ultramafic vulcanism.
