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Earth's magnetic field is maintained by the dynamo effect, and I have no doubt that this effect could sustain Earth's magnetic field for a very long ("infinite") time.

It's my understanding that the energy flow is as follows. Thermal gradients in the liquid metal and differential rotating inner iron core and inner mantle yield kinetic liquid metal energy, which results in viscous dissipation losses, and magnetic energy, which results in joule heating.

The differential rotating inner iron core and inner mantle is fueled by the conserved angular momentum of the rotating earth. The same side of our moon always faces us due to (I think) tidal locking (water tides on the moon slowly stripped its angular momentum).

Here's my question:

  1. Can we lose the energy source from differential rotating inner iron core and inner mantle over time by losing the differential rotation?

  2. If the answer to 1. is "yes", then will the other input energies be enough to maintain Earth's dynamo?

  3. If the answer to 2. is "no" or "maybe", then can we compute a time estimate of how long that will take? How long will it take?

Any help is greatly appreciated!

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  • $\begingroup$ Angular momentum is only conserved for a point mass in a perfectly symmetric radial potential. This is not given, there are tidal forces by the other planets. There are radioactive decays inside the earth that heat it up. Energy is dissipated into the universe. I think it is hard to make an estimate on the relative sizes of the effects out of the blue. $\endgroup$ Commented Oct 1, 2016 at 12:57
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    $\begingroup$ The dynamo is driven by convection, not differential rotation.The core is at 5,700 K and cooling about 100 degrees Celsius per billion years. $\endgroup$ Commented Oct 2, 2016 at 1:47
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    $\begingroup$ This answer over at Earth Science StackExchange suggests the earth's core has cooled by about 250 K over the last 4 billion years, so I doubt that the losses you mention in the 2nd paragraph are particularly strong. $\endgroup$
    – Kyle Kanos
    Commented Nov 24, 2016 at 16:56

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Well the magnetic field is losing energy because its energy in Earth's outer liquid core is losing energy. However the amount of energy lost is so little it does not change a lot of things. It will probably takes 8 billion years before the magnetic field truly fails. The energy lost by the magnetic field usually gained back by the Earth has the magnetic field goes back towards Earth's core. Earth's core gains a small amount of energy from solar radiation as it hits upon Earth's magnetic field. The magnetic field takes up energy and drops it in the core. Also radioactive decay heats up Earth's core.

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    $\begingroup$ Any source for the 8 billion years figure? $\endgroup$ Commented May 4, 2023 at 13:52
  • $\begingroup$ It is a rough figure $\endgroup$ Commented May 6, 2023 at 13:22
  • $\begingroup$ I mean it will not decay before the sun swallows the Earth $\endgroup$ Commented May 6, 2023 at 13:22
  • $\begingroup$ I think it is rather misleading to throw in a number like that if what you actually mean is "Earth only has 8 billion years left before the sun gets it". Many will read it as if there was a known result of a decay rate, rather than a separate time limit. $\endgroup$ Commented May 7, 2023 at 23:52
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The short version is: 1.yes 2.no 3.we (probably) don't have enough information about the core.

Sustaining the dynamo would violate the conservation of energy. Further, to find the answer our margin of error would likely be proportional to the losses we would be chasing. We would need to ultimately model the interior of the sun.

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