Almost a century ago,or perhaps more than a century ago, science determined from the knowledge that the earth had a magnetic field that the only place it could have been generated was in the core via a dynamo mechanism. Science then did not know about the solar wind, electrified space plasma or the Van Allen belts. Science could not have explained it any other way. Science did not know about space electricity so the standard model then involved a simple radiating sun, and inert matter-less space in which were suspended planets all behaving according to the laws of motion described by Isaac Newton. Science knew about electric currents in wires and the generation of magnetic fields, but as science also was totally ignorant of space plasma, the earth-centred dynamo theory was the only plausible explanation possible.
Fast forward to 2014 and we now know about space plasma, the Van Allen Belts, the solar wind, electric plasma, magnetic flux tubes and Birkeland currents. Knowing what we know about how to generate a simple dipole magnetic field using a coil of wire and a conductor inside the coil, it is strange, is it not, that we still stick to the belief that the geomagnetic field is produced in the earth’s core by the dynamo model.
But if we know that the Van Allen belt is simply a torus of electric charge rotating around the earth’s ‘axis’ and that this is an analog of a simple solenoid made of a length of wire wrapped around a conductor, and then asked what is generating the geomagnetic field, one would preferentially use the solenoid model as the explanation, realising that no one has yet been able to generate a magnetic field from rotating a liquid conductor. Science is all about using the known to explain observations.
However the religious mind will stay with the earth-centred dynamo model while the scientific mind, cognisant of new data, would realise that it is more likely that the geomagnetic field is produced by the Van Allen Belts than by some some unobserved dynamo model in the earth’s core.
And this present model will be probably falsified or improved with additional knowledge as time goes on but it will do as a starting point.