Consistency of Earth’s magnetic field history surprises scientists

Washington, D.C.—Earth’s magnetic field is generated by the motion of liquid iron in the planet’s core. This “geodynamo” occasionally reverses its polarity—the magnetic north and south poles swap places. The switch occurs over a few thousand years, and the time between reversals can vary from some tens of thousands to tens of millions of years.

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—the time when animals have roamed the Earth’s land and seas—there are three known superchron periods, occurring about once every 200 million years.