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Comment by rr808 | Hacker News Reader

Its like 100 degrees all week in Utah. Maybe you can generate electricity but surely geothermal is best for heating in the cold?

Is the molten core of the Earth so hot that its inexhaustable? I'm wondering if it cools if that could potentially cause any issue. At least I'd think a warming planet doesn't need that extra heat on the surface.

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> Is the molten core of the Earth so hot that its inexhaustable?

AIUI it's effectively inexhaustible. Earth's core is gradually cooling but we're talking something like 100C per billion years, for something presently at like 5,400C.

So as far as human activity is concerned, it's an infinite source of heat.

Edit: it's worth keeping in mind the Sun has something like 5B years before it turns into a red giant which is game over for Earth regardless of how much energy remains in its core.

Wouldn't the pressure of all the weight of the planet itself trying to press down on a single point eventually lead to a heat equilibrium?

This isn't my area of expertise, but my high-level lay understanding is the core is spinning at a rate faster than the crust.

I suppose when it all slows down and the spin rates from core to crust converge, it will all settle down and cool. But I think that's also when you lose the magnetic field...

Would love for someone better versed in earth's geophysics to chime in!

In addition to that taking a couple billion years, earth is also heated by fission to a fairly substantial degree which slows down equilibrium further.

You don't even need gravity. Basic thermal dynamics says that a closed system should reach thermal equilibrium. It is (in my opinion) actually a bit surprising that a massive body in thermodynamic equilibrium has a uniform temperature. Assume the planet is an ideal gas. Applying P=VT, you might intuitively expect temperature to rise as you approach the center, since pressure rises as you do so. However, this analysis ignore the V portion of the equation. Consider a cylindrical cross section going up from the center of the body. Define a series of slices of this cylinder, such that each slice has N particles. Assume that N is sufficiently small that the gravitational and pressure gradient is negligible within each slice. As you descend along the cylinder, you will find that while pressure increases, it is the volume of each slice that decreases, leaving temperature as a constant.

All of this assumes Newtonian gravity. I believe if you consider relativistic effects, you find a slight temperature gradiant where temperature decreases as gravitational potential increases.

A simpler explanation: if the center of the earth-gas was hottest, it would heat up the area around it, which would heat up the area around it, etc. eventually there would be no temperature gradients left!

> Edit: it's worth keeping in mind the Sun has something like 5B years before it turns into a red giant

AIUI we have about 1 billion years before the sun's output has increased enough that liquid water will not be able to exist on the surface of the planet, which means it's pretty much game over for life on earth at that point too.

not only is it very hot, it's also very big, and so whatever we pipe down there is negligible in size and thus not going to cool the very big hot thing very quickly.

earth's magnetic field is created by electric currents that are created by convection currents in the iron of the earth's core. As the earth's core cools, it will decrease the strength of its magnetic field and allow increasing amounts of solar wind (charged particles from the sun) that will destroy the ozone layer and lead to the eventual dissipation of the atmosphere. This is probably what happened to mars.

Heat probably comes from Natural Nuclear reactions. When a planet forms the heaviest elements go to the center - so it intuitively makes sense that Uranium will be concentrated enough for fission reactions to start and continue.

> At least I'd think a warming planet doesn't need that extra heat on the surface.

Despite the downvotes, this is correct. All electricity ultimately end up as heat in the atmosphere.

Ideally we would need a power source that EXTRACTS energy from the atmosphere. So that the electricity lifecycle would be thermally neutral.

We are already heating the planet by burning fossil fuels, and that has the double-heating effect of emitting gases which further trap heat, mostly from the sun.

The heat emitted by burning fossil fuels is completely irrelevant compared to the greenhouse impact. We burn about 11.7 gigatons of oil equivalent a year, which over 200 years would be 2.7 * 10^16 kWh. The greenhouse effect increase over the last 20 years leads to over 2.2 * 10^15 kWh/yr added to the planet, over 20x as much.

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