Science Daily Geology
Earth's magnetic field occasionally reverses its polarity -- the magnetic north and south poles swap places. When magnetic polarity remains stable in one orientation for more than 10 million years the interval is dubbed a 'superchron.' Within the last 540 million years there are three known superchron periods. New work identifies up to 10 additional superchrons over 1.3 billion years during the Proterozoic Eon, Earth's middle age, which occurred 2.5 to 0.54 billion years ago.
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