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Since the magnetic field of the earth, which protects us from the solar winds among other things, is generated by spinning of the molten outer core, do you happ

by dsp1234 10y ago

Since the magnetic field of the earth, which protects us from the solar winds among other things, is generated by spinning of the molten outer core, do you happen to know how much of that energy would be available before adverse effects happen? It's obvious that the answer is less than 100%, since a completely solid core would provide no magnetic field. Is there some way to tell whether it's closer to 0.1%, 1% or 10%?

dpark 10y ago
Let's assume it's not just 0.1% but 0.001%. That still leaves us a comfortable runway of 19 million years at our current levels. But also let's hope it's not 0.001% because I'm pretty sure the core will cool more than that on its own over a shorter timespan than 19 million years.
- nitrogen 10y ago
  Won't thorium decay keep it warm for a good long while?
  - dpark 10y ago
    I'm honestly not sure. I don't know how much energy is being created inside the Earth and how much is just residual. It's my understanding that the Earth is slowly cooling, though, so radioactivity isn't replenishing heat as rapidly as we're losing it.
- drivebyneatfact 10y ago
  Wikipedia suggests cooling of 100 degrees C every billion years. 19 million years is 1.9% of the billion year rate. So it suggests the core should lose 1.9C in 19 million years. That's about 0.035% of the total temp, using Wikipedia's 5700C as the temp estimate. That's a great initial guess, given how much uncertainty is (i've recently heard core temp could be 4x the wiki number, and some people estimate the earth's core only has lost a few degrees since it formed, rather than nearly 500 degrees). Neat stuff, thanks for providing the opportunity to look in to this.
Tuna-Fish 10y ago
The 80 million years figure is for the heat content of the crust, not the entire earth. The heat content of crust is approx 0.04% of the heat content of earth. It's not really possible to use enough geothermal for it to have a noticeable effect on the lifespan of the magnetic field. Even completely removing the solid crust of the earth would not really register.
- dsp1234 10y ago
  This is a really great point, and probably the key one. It's also probably a good assumption that heat extracted from the Earth's crust after some point would stabilize due to heat differential from the layer's beneath the crust. So we could take out some percentage of the heat of the crust, thus lowing the total temperature by some amount, but then that loss would be replenished from further down in the core. It looks like from the calculations elsewhere in the thread that it probably wouldn't even be physically possible to extract that much energy from the crust. We'd just run out since there would be some lag time in replenishing the heat from the core through to the areas of the crust.

by dsp1234 10y ago

dpark 10y ago

Let's assume it's not just 0.1% but 0.001%. That still leaves us a comfortable runway of 19 million years at our current levels. But also let's hope it's not 0.001% because I'm pretty sure the core will cool more than that on its own over a shorter timespan than 19 million years.

nitrogen 10y ago
Won't thorium decay keep it warm for a good long while?
- dpark 10y ago
  I'm honestly not sure. I don't know how much energy is being created inside the Earth and how much is just residual. It's my understanding that the Earth is slowly cooling, though, so radioactivity isn't replenishing heat as rapidly as we're losing it.
drivebyneatfact 10y ago
Wikipedia suggests cooling of 100 degrees C every billion years. 19 million years is 1.9% of the billion year rate. So it suggests the core should lose 1.9C in 19 million years. That's about 0.035% of the total temp, using Wikipedia's 5700C as the temp estimate. That's a great initial guess, given how much uncertainty is (i've recently heard core temp could be 4x the wiki number, and some people estimate the earth's core only has lost a few degrees since it formed, rather than nearly 500 degrees). Neat stuff, thanks for providing the opportunity to look in to this.

Tuna-Fish 10y ago

The 80 million years figure is for the heat content of the crust, not the entire earth. The heat content of crust is approx 0.04% of the heat content of earth. It's not really possible to use enough geothermal for it to have a noticeable effect on the lifespan of the magnetic field. Even completely removing the solid crust of the earth would not really register.

dsp1234 10y ago
This is a really great point, and probably the key one. It's also probably a good assumption that heat extracted from the Earth's crust after some point would stabilize due to heat differential from the layer's beneath the crust. So we could take out some percentage of the heat of the crust, thus lowing the total temperature by some amount, but then that loss would be replenished from further down in the core. It looks like from the calculations elsewhere in the thread that it probably wouldn't even be physically possible to extract that much energy from the crust. We'd just run out since there would be some lag time in replenishing the heat from the core through to the areas of the crust.