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Q & A: Flipping the Magnetic Field of the Earth

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Magnets
Earth & Moon
Q:
has the magnetic fieldof the earth ever flipped?
- Anonymous
A:
Yes, the magnetic field of the Earth has flipped several hundred times, in the past.  Such an  event is called a "geomagnetic reversal."

The magnetic field of the Earth is generated by the hot molten metal beneath the crust in the core and mantle.  This mixture of molten metals rotate within the Earth and generate the magnetic field lines around our planet.  However, this sea of molten iron is hot, dense, and chaotic and is subject to unpredictable changes.  These fluctuations in the source of the magnetic field are what's causing the magnetic poles to "drift" around on the surface of the Earth (the North Pole is not at the very "top" of the world, where you would expect it to be; in fact, right now it is in Northern Canada and making its way toward Siberia in Russia).  Occasionally, at seemingly random intervals, the poles of the Earth flip-flop.

The interesting thing is that geologists can map exactly when these reversals have occurred, because information about the Earth's magnetic field gets locked into rock that is pushed up from the mantle.

For more information, this article sums it all up quite nicely with great illustrations: Earth's Inconstant Magnetic Field

Thanks for the question,
Jim

(published on 02/16/2011)

Follow-Up #1: Earth's magnetic field reversal

Q:
I have read that the Earth's magnetic field reverses itself every 70 million years or so, and we are long over due. During the period of a reversal, there could be a period where there is no magnetic field whatsoever. This poses a huge peril to the earth, as it's magnetic field protects it from harmful effects of the sun. I was wondering, would it be possible to "reproduce" the earth's magnetic field, artificially? If so, how could this be done?
- James (age 42)
Baltimore, MD
A:
The reversals are recorded in magnetic rocks. They occur irregularly, but usually much more frequently than every 70,000,000 years. In fact, they typically happen in less than a million years. Since the timing is so irregular, there's no particular time when one is due, and thus no sense in which one is overdue. It is true that in recent years the field has been changing fairly quickly, so that there may be a reversal coming in the next few thousand years.

It's not true that there's no field during a reversal. Only the dipole moment of the field goes through zero, leaving a more disorganized field pattern. Although one would still expect that the increased radiation would have major effects on life, there's little evidence of that in the fossil record of past reversals.

I don't see how people could set up such a large-scale field.

There's a nice article, with pictures, on Wikipedia:
http://en.wikipedia.org/wiki/Geomagnetic_reversal.

Mike W.

(published on 12/13/11)

Follow-up on this answer.