This article on Earth’s Dynamo Effect states:
Assume first (A) that there is present an initial poloidal magnetic field
My simple question is what is the source of this initial field?
Sounds like homework. Did you actually read the link?
Yes I did read the link. It merely states the need for an existing field and it is the source of this existing field I am interested in. And no, this is NOT homework. I’m 58 years old, my homework days are long past!
The sun, perhaps? Its magnetic field is weak out at Earth, but it isn’t zero. The dynamo effect is self-reinforcing and only needs a weak initial field to get going.
The Sun’s magnetic field is itself due to a dynamo. Dynamos generate their own magnetic fields.
Yes, but this is a chicken and egg question. Given a spinning molten sphere of metal with some internal turbulence, with no magnetic field present, whence comes the initial spark to begin the process?
For something like the Earth, clearly the sun is as good a source of a field to kick things off as any. But we assume it got kicked off itself in the dim dark past, and so on back to the early universe. Something initiated an inhomogeneity in the magnetic field. Magnetic monopoles? Quantum fluctuations in the first moments? Some more classical macroscopic phenomenon? Do fluctuations in the modern universe provide enough to kick a process off given enough time?
I rather hope it is monopoles.
Any trace source of magnetism could get things started, and all matter has traces of magnetism.