
Earth as a nuclear furnace (geothermal heat is mostly from radioactive decay) - iwwr
http://en.wikipedia.org/wiki/Geothermal_gradient
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hartror
The beauty of this is geothermal heat adds the opportunity for life to
develop/survive outside the Goldilocks Zone [1]. Not just in our solar system
where the moons of Jupiter and Saturn are very active geologically due to
tidal forces [2] but on extrasolar moons and planets that otherwise may not be
suited to life.

Perhaps there is more life in the universe where the base energy source is
that of geothermal than that of radiation from a star? I wonder what an
sentient life form evolved from this environment would be like?

I feel a short story coming on.

[1] <http://en.wikipedia.org/wiki/Habitable_zone>

[2] <http://en.wikipedia.org/wiki/Tidal_force>

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ars
The long term stability of such a heat source is poor (it would start very
hot, then cool exponentially). But it's an interesting idea.

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jarin
How long is long term though? If I'm reading this right, the highest generator
of heat is naturally radioactive thorium, which has a half-life of about 14
billion years. The Earth is only about 4.54 billion years old.

~~~
ars
No, thorium is the lowest, not the highest. It decays too slowly to be a large
source of heat.

Potassium-40 (1.2 billion years) is the highest.

~~~
jarin
The article says that thorium releases 3.27×10^-12 Watts of heat per kg of
mantle, while potassium releases 1.08×10^-12 Watts.

Isn't that more, or do I just fail at basic math?

~~~
ars
I got my info from here:
[http://www.berkeley.edu/news/media/releases/2003/12/10_heat....](http://www.berkeley.edu/news/media/releases/2003/12/10_heat.shtml)
which said potassium. Shrug.

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radu_floricica
I'm surprised of how little potential geothermal has as a sustainable energy
source. The total heat flow from the earth is 42 TW, and wikipedia says world
energy consumption in 2008 averaged at 15 TW. We'd need a better then 30%
global efficiency to use geothermal exclusively long term. This pretty much
makes geothermal non-renewable...

Solar energy on the other hand clocks at 173 petawatts (of which 30% is
reflected, so that makes it 120).
[http://en.wikipedia.org/wiki/Earths_energy_budget#Incoming_e...](http://en.wikipedia.org/wiki/Earths_energy_budget#Incoming_energy)

~~~
bobds
Did that Wikipedia article disappear in the one hour since you've linked to
it?

EDIT: Never mind, correct link:
<http://en.wikipedia.org/wiki/Earth%27s_energy_budget>

~~~
radu_floricica
We should make it a standard that url's be copy-pastable. Sorry and thank you.

