No, this post isn’t about racing cars, it’s about the Earth’s poles. Not much interesting to tell about those, you say? Guess again.
What are they?
There’s two, right? One south, and one north. Actually, it’s slightly more complicated than that. There are actually three ways to look at the poles. There’s the magnetic poles, the geomagnetic poles, and there’s the geographic poles. And those are not the same things. They’re not even in the same places, in fact.
The magnetic poles
When you magnetize a sliver of metal and make sure it can move freely, it will rotate to a position where it faces south-north. For example, you can rub a needle against a magnet, then suspend it in a cup of water. The surface tension keeps the needle afloat, and the Earth’s magnetic field makes it point north.
Earth’s magnetic field is generated by the Earth’s core. The field is the result of conductive molten materials in the core, like iron. The Earth rotates, causing kinetic energy in the core, which makes the core act like a magnet. The poles of this magnet are at the magnetic north and south pole of the Earth.
If you were to be at exactly the magnetic north pole, your compass would want to point straight up into the sky.
The geomagnetic poles
What I wrote above is true, but it’s not the whole story. The Earth magnetic field behaves mostly like a magnet, but it doesn’t behave exactly like a magnet.
While a compass might point at the magnetic pole, the center of the so-called magnetic dipole field lines is actually not at the magnetic poles. This leads to a set of two other ones: the geomagnetic poles.
The geographical poles
The Earth rotates around its own axis. The axis around which this happens has the north and south geographical poles at its ends. These poles are the places where the longitudinal lines on a globe come together. They are, in other words, located at a latitude of 90 degrees.
The poles, because they are at the rotational ends of the Earth, have exactly six months of daylight and six months of darkness.
The (geo)magnetic poles are generated by flowing magma, which isn’t completely uniform. This means the magnetic poles don’t coincide exactly with the geographic poles.
And so there are six.
Moving targets
It gets more interesting. Not only are there six different poles that don’t line up. They all move around.
The magnetic poles are formed by flowing magma, which moves and changes, and shifts the magnetic pole to different locations over the course of decades and centuries. The geomagnetic poles move for the same reason.
The geographic poles also move. If the Earth were completely static, this wouldn’t happen. However, it isn’t. The distribution of mass around the globe changes. One way this happens is our daily tides, but those change rapidly and form a stable pattern, meaning it won’t affect the geographic poles. What does affect them, is the ice sheets in the north and south.
Yep, that’s right, another change that global warming causes is the actual shift of the Earth’s geographic axis. Because the ice caps are melting, and large volumes of water go from the poles to elsewhere, the mass distribution of the Earth changes and the Earth’s poles moves. This shouldn’t be dangerous, but it’s still a bit frightening. I mean, we’re unbalancing our home planet. We really don’t have a spare if we break it.
Magnetic reversal
There’s still more to tell. From looking at old layers of volcanic rock, scientists have determined another major change that the Earth’s magnetic field undergoes. Every so often, the field reverses. The north and south magnetic poles switch.
This reversal happens at random intervals and occur quite rapidly. It is certain that at some not so-distant future point in time, our compasses will start to point at a different place each year, until they all point completely south. This could happen within a single human lifetime.
Shield
Then finally, maybe the most important bit of information regarding the Earth’s magnetic field. Without the Earth’s magnetic field we’d all be dead.
That’s right. We’d all be dead.
You see, the Earth’s magnetic field protects the Earth from harmful solar winds. These solar winds would strip away our ozone layer. That in turn would cause a bombardment of the Earth with harmful radiation. After that the solar wind would start to strip off our atmosphere, leaving Earth in a similar state to Mars: cold and uninhabitable.
Bottom line: Yeah for the Earth’s magnetic field.
Oh, and one corollary for science fiction fans and writers: a planet that doesn’t rotate has no magnetic field and thus possibly no atmosphere and lots of radiation. Plan your alien life accordingly.
