I don't have the requisite knowledge in this field to attempt to prove or disprove anything. All I can do is present information. Perhaps others can provide some answers one way or another, but those with said knowledge remain quiet so I suppose it'll just stay a mystery.
The dynamo theory was the only thing I've heard on this, from what I've followed casually; and it makes a good deal of sense, so I've not questioned it. The only real question I have with the dynamo theory is why ours is still working, and why Venus and Mars are not. Until we actually know the makeup of planetary cores though, that won't be answered.
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