|MadSci Network: Earth Sciences|
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!
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