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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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