Thank you, everyone, for your thought-provoking responses. The crux of the problem seems to be the source of the initial magnetic field which kicks the dynamo process off. As near as I can tell, there is no consensus on where this comes from, although there are many theories. Some or all of them could be partially correct, or they could all be incorrect as there is lots we still don't know. Nevertheless, we must assume that such a seed magnetic field exists, regardless of its source. Also, from the discussion, it seems that the initial magnetic field would not need to be particularly strong, to get things going.
I would also like to thank chatGPT 4.0 for its thoughtful response on this subject. Up until now, it has largely responded to my questions with nonsense. The latest iteration seems quite impressive. Perhaps others have even better insights, but here is a summary of its "thoughts" on the source of the initial magnetic field needed to kick things off:
The exact origin of the initial (seed) magnetic field that kick-started the Earth's geodynamo is not known with certainty. Several hypotheses exist, but none have been definitively proven. Here are some leading theories:
Primordial Magnetic Field:
This hypothesis suggests that the initial magnetic field could have been inherited from the magnetic field of the solar nebula, the cloud of gas and dust from which the solar system formed. As the Earth formed, it might have retained a small portion of this primordial magnetic field.
Early Dynamo Processes:
In the early history of the Earth, before the core fully differentiated, there could have been early dynamo action in the partially molten planet or proto-core. These processes might have generated a weak initial magnetic field.
Thermochemical Processes:
Chemical reactions during the differentiation of the Earth, as the core separated from the mantle, could have produced electrical currents that generated a magnetic field. These processes might have included the crystallization of certain minerals or the movement of fluids within the young Earth's interior.
Impact Events:
Large impacts during the Earth's formation could have temporarily generated magnetic fields through shock-induced currents. These impacts might have left behind a residual magnetic field that could act as a seed for the geodynamo.