Reversals of the Earth's Magnetic Field

AMONG the many surprising results of studies of the natural remanent magnetization of rocks1, one of the most curious has been the conclusion that the Earth's magnetic field has undergone changes of polarity; that, in fact, reversals of the main field have been a persistent feature of its behaviour. Normal and reversed fields could equally well exist, according to the dynamo theory of the Earth's magnetism2, but it is not known whether a means of transfer from one field to the other exists.

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