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Most of us like stability in our lives, especially when it comes to planet-wide phenomena, such as the daily appearance of the sun or the periodic change of season. So it can be unsettling to learn of global phenomena that are inherently unstable, unpredictable. Such is the case with the Earth's magnetic field. Every so often, our planet's magnetic poles reverse polarity (see When Compasses Point South). Compass needles have always pointed north; in a reversal, they would point south.
You could perhaps take comfort in the knowledge that these reversals happen infrequently—on average every 250,000 years—but maybe not when you consider that it's been over 700,000 years since the last reversal, and the next one may be currently underway.
The Earth's magnetic field is created deep within our planet's outer core through a complex, self-sustaining interaction known as the "geomagnetic dynamo" (see What Drives Earth's Magnetic Field?). In the 1980s, Gary Glatzmaier, now at the University of California, Santa Cruz, and Paul Roberts of the University of California, Los Angeles, began work on a computer model that simulates this interaction. By 1995, they had created a model that not only created a self-sustaining magnetic field (the first to do so), but after simulating the passage of 36,000 years, the field it generated spontaneously flipped.
Here, view the animation generated by the Glatzmaier-Roberts computer model and see what happens during a reversal.
—Rick Groleau
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