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AgnosticStopSign t1_iuqfduz wrote

Reply to comment by vfstevens in Drilling 12 Miles Down to Tap Geothermal Energy by tonymmorley

Theyll say its negligible until everyone is tapped in.

The energy will be transferred from the core to electricity, and it will eventually have a noticeable effect on the core. Whether its 100 years or 10000 years, imo, is inconsequential considering the consequences of a no longer spinning, magnetic earth.

But these same people will say “X has 200 years of oil in a reservoir” and never think further, such as: then what? Specifically, what happens to the area the oil had filled, and what will you do when its gone?

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taz-nz t1_iuqjetg wrote

The Earth's core radiates somewhere around 47TW into space, which is largely replenished by radioactive decay. You could power the whole planet with nothing but geothermal from now until the Sun shallows the Earth, and you would only cool the core by 1-2%

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AgnosticStopSign t1_iuqjong wrote

Ok what are the implications of a 1-2% decrease?

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taz-nz t1_iuqmo10 wrote

Basically nothing, the core is 4000-6000 Deg C, iron melts at 1538 Deg C, we are talking lowing it by 40-60 Deg C over 8 Billion years.

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UnifiedQuantumField t1_iuqvqtb wrote

> the core is 4000-6000 Deg C

This might be a bit of a side track but here goes anyways...

The currently accepted explanation for this temperature is "decay of radioactive elements within the mantle".

But I suspect that something else is going on. How so?

>The Earth's core radiates somewhere around 47TW into space

Is there really that much radioactive decay going on? Has anyone ever done any calculations to see how much decay of whatever elements would be needed to produce that much energy? Can the process of radioactive decay produce that high a temperature (roughly equal to the surface temp of the Sun)?

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taz-nz t1_iur3z4i wrote

Did a little bit more digging, the radioactive decay account for about half the heat being given off 20+TW. The rest is the heat from earth formation and the huge pressures created at the core by earth mass and gravity.

What you have to remember is the earth is really big, and when the earth first formed and was a hot molten ball, most of the heavy elements like iron, uranium and thorium sank deep into the core.

Iron makes up 80% of the inner and outer core, but isn't anywhere near that common on the surface, same goes for Uranium and thorium, while they aren't that common on the surface they are much more so in the core, thus the core has a lot more radioactive decay.

The thermal output of the core was calculated by drilling hundreds of deep boreholes and calculating the heat transfer through the earth crust.

While 47TW may seem like a lot, it's nothing compared to the 173,000TW of energy the sun baths the earth in. (thus the reason why greenhouse gases trapping even a tiny percentage more of the suns energy is very bad)

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