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The Dynamo theory gives a good explanation of the magnetic field of the Earth: the Coriolis force focus inner currents into current spirals generating magnetic(s) field(s).

What I'm trying to understand is the origin of these inner currents.

For currents to appear, there should exist charges moving. If such important charges exist, there is one or many mechanisms at work to separate positive and negative ions. Of course among these mechanisms a magnetic field acting on currents is a pretty good explanation (see What is the source of Earth's magnetic field: a magnetic field on a rotating conducting fluid is able to create currents and these currents in turn will create a magnetic field). But at the same time this loop between cause and effect isn't completely satisfying and should have been started in an external way.

What might have started an unbalance in positive and negative ions inside Earth to bootstrap inner currents and then its magnetic field?

What process might explain the starting of the magnetic field of the Earth without the hypothesis this magnetic field was already there?

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    $\begingroup$ I think this is largely covered by What is the source of Earth's magnetic field?. The field is self amplifying, so even the tiniest random field would be amplified up into the field we observe today. Where that initial tiny random field came from no-one knows. It could be a thermal fluctuation or even the influence of the Solar wind. $\endgroup$ Jun 30 '16 at 9:57
  • $\begingroup$ Your comment is a candidate pretty good answer :) . $\endgroup$
    – dan
    Jun 30 '16 at 10:38
  • $\begingroup$ Other good possible explanations? $\endgroup$
    – dan
    Jun 30 '16 at 10:39
  • $\begingroup$ If such a self amplyfing loop is at work (Coriolis + Lorentz) why isn't the Earth's magnetic field causing a magnetic Larsen effect? $\endgroup$
    – dan
    Jun 30 '16 at 10:43
  • $\begingroup$ Presumably there are other mechanisms that limit the maxmium field strength. $\endgroup$ Jun 30 '16 at 11:00