Earth’s Magnetic Field: Reversal
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When a compass needle points towards geographic north, it’s actually pointing towards the south pole of Earth’s magnetic field. Over the lifetime of our planet, the Earth’s magnetic field has reversed the direction of its polarity a number of times. I’m Jim Metzner, and this is the Pulse of the Planet. Gary Glatzmaier is a Professor at University of California in Santa Cruz.
“It’s a magnetic field that’s slowly changing, and occasionally, you get magnetic field reversals. In other words, where you had a magnetic north pole, switches to a magnetic south pole and vice versa. In fact, right now, the north geographic pole – somewhere over the Arctic – that is actually a south magnetic pole, and the north magnetic pole is somewhere down in the Antarctic.”
To find out why Earth’s magnetic field reverses its polarity, Glatzmaier developed a computer model which simulated conditions in the Earth’s interior over many thousands of years, paying particular attention to the flow of movement in the Earth’s molten core. Here’s what he learned….
“There are instabilities occurring in the fluid flow, places where the fluid changes its direction, like little hurricanes or little storms. And this generates slightly different magnetic fields, different polarity from the basic polarity that exists at that time. There’s always these instabilities occurring. Typically, they don’t last. But once, in many attempts, one of these little instabilities, for some reason, everything’s favorable so that its different polarity its reversed polarity – continues to be generated, while the original polarity actually starts to decay away. And when this happens, there’s a chance that the new polarity will continue to grow and take over the entire core of the Earth, and the original polarity completely decays away. Now, this process, if it happens, will take on the order of several thousand years.”
We’ll hear more about Earth’s magnetic field in future programs. Pulse of the Planet is presented by the National Science Foundation.