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How long has the earths magnetic shield existed?

April 26, 2017earth existed MAGNETIC Shield

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How long has the earths magnetic shield existed?

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When magma cools and solidifies to form igneous rocks, some of the minerals may preserve a record of the magnetic field strength and direction at that time. From this, scientists have been able to construct a record of field strengths and geomagnetic reversals going back at least 160 million years. Therefore we have good proof that the magnetic field has been around for at least that long.