Re: hypothes on the earths magnetic field. What are they?

I don't believe there is another theory which is being considered
for the source of the Earth's magnetic field. Textbooks state that
the fact that the Earth's core contains a core of molten rock provides
good evidence for the existence of a magnetic field and the fact
that the direction of that magnetic field reverses over millions
of years. Also, other planets in the solar system
which are known to have magnetic fields (Jupiter and 
Saturn for instance) are also thought to have liquid 
cores. Scientists are still trying to better understand the
exact origin and affect of the Earth's magnetic field on our
atmosphere. Thanks for such an interesting question!