About Polar Reversal

Cause of the Field

• According to the National Aeronautics and Space Administration (NASA), there's a giant ball of iron at the center of the planet, about 70 percent the size of the moon and as hot as the sun's surface; it also spins slightly faster than the rest of the Earth. Surrounding this ball is a sea of electrically conductive liquid iron. The dynamo action created as this charged ocean flows over the solid iron core generates electromagnetic energy that "radiates" magnetism from the poles of the core -- similar to the way a spinning pulsar shoots gamma radiation from its poles.

It's Changing

• Because a turbulent and roiling ocean of liquid iron generates the magnetic field, the field is susceptible to changes. The magnetic poles can reverse over a few thousand years. Throughout the 20th century, NASA says the North Pole moved roughly six miles per year. Now NASA says the move is about 25 miles per year; in a few decades, the magnetic North Pole will be in Siberia rather than on the fringes of North America. Scientists know that polar reversal has happened before from studying the planet's paleomagnetic record -- the way Earth's magnetic field has affected rocks -- and say the last reversal happened about 780,000 years ago. According to the American Geophysical Union, these reversals can be triggered by events that affect the flow of iron in the core. Large impact events, such as a meteorite striking the Earth's surface, can send shock waves to the core that start the process of a polar reversal. Reversals may not be fully realized until thousands of years after such an impact.

Weakening

• The magnetic field is weaker than it has been in the past, but Gary Glatzmaier, a professor of earth and planetary sciences at the University of California, Santa Cruz, says that's nothing to worry about. The dynamic electromagnetic forces at the center of the planet operate like an ocean -- sometimes violent and other times calm. This diminution of the magnetic field is part of the shifting and changing that occurs in the core while a reversal is happening. Because the planet's core is essentially an ocean of iron, think of this as like the ebb and flow of tides in the surface ocean. Since the 19th century, the planet's magnetic field has lessened by about 10 percent, but Glatzmaier says it's a minor fluctuation compared to past behavior.

It's Not Dangerous

• NASA says polar reversal is a perfectly natural phenomenon. Regardless of the directions of the poles, the magnetic field will still protect the planet from solar storms and extraplanetary radiation.