The Earth As a Magnet

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The response of a compass needle to the force exerted by the Earth shows that the Earth behaves like a giant bar magnet. Its magnetic field extends for hundreds of miles into space.

However, the magnetic North Pole to which the needle points, doesn’t coincide exactly with the geographic North. As the Earth rotates, its liquid iron core rotates with it. Since rotating conductors of electricity produce magnetic fields as they move around, the constant movement of the outer liquid core relative to the solid inner core generates electricity. This in turn produces a magnetic field.

Right now the North Pole of the Earth’s magnetic field is in the Canadian Arctic. However, the Earth’s magnetic field has undergone several reversals in the past, so that the North Pole was once in the south - where Antarctica is now.

One of the enduring mysteries of science is to understand how the Earth could have a steady magnetic field that changes direction every once in a while. Fortunately, however, rocks remember where the Earth’s magnetic field used to be. Discovering frozen magnetic material pointing south instead of north helps us understand that the north pole of the Earth was the south pole when the rock hardened.

So next time you’re lost in the woods, be thankful that the Earth’s field won’t be changing any time soon.