[ExI] Efficiency of wind power

[Kelly Anderson]

2011/4/9 John Clark <Jonkc at bellsouth.net>:
> On Apr 9, 2011, at 2:03 AM, Kelly Anderson wrote:
>
> Given that the core is heated by nuclear fission,
>
> Geothermal heat does not come from nuclear fission, 80% of it comes from the
> decay of radioactive isotopes, primarily Potassium Uranium and Thorium; the
> remaining 20% comes from the formation of the Earth when a large cloud of
> matter was compressed by gravity into a small ball 8000 miles in diameter,
> all that gravitational potential energy was converted into heat.

Thank you very much for this clarification. I somehow missed the
difference between fission and nuclear decay. Lord Kelvin estimated
the age of the earth at something around 8000 years based on the
cooling without the nuclear component... what is science's best guess
as to when the decay of isotopes will stop? Is it before or after we
are swallowed by the sun? I ask because it seems bad things happened
to Mars after it's core became more solid and it lost it's
magnetosphere.

I would add that a lot of the initial heat in the formation of the
earth came from the impacts of comets and asteroids into the earth.
This may be what you meant by gravitational potential energy converted
into heat, but the picture is so much more vivid when you look at
comets slamming into a molten orb at 20,000 MPH! :-) That's a LOT of
heat, although assuming Kelvin was right about that part, it seems not
to account for the majority of the heat over the eons... but I don't
know if Kelvin was correct even on that point. He may have just been
trying to match the Biblical numbers with pseudo science.

-Kelly