What Causes the Earth's Magnetic Field?

Just where did our protective magnetosphere come from? We take a look at the Earth's magnetic field and how it interacts with the Sun.

Any magnetised material is bipolar, meaning it has a north and south pole, and the magnetic field lines run from north to south. The magnetic field lines at the north pole swing back to the south pole, creating an external magnetic field outside the material that can affect other things that get too close.

You're most likely familiar with a bar magnet, and in essence, Earth's magnetic field is very similar to that; consider an enormous bar magnet running through the core of Earth from pole to pole, and you'll be able to get the picture. However, Earth's core is molten, so a circulating electric current at the core induces our planet's magnetic field. One of the results of this is that, on rare occasions, Earth's magnetic field can flip. This is thought to occur once every 200,000 years on average.

Taking the 'bar magnet' through Earth analogy further, it just so happens that the south pole of Earth's magnetism is at the geographic north pole, and the north pole is at the geographic south pole. When somebody refers to 'magnetic north', they are referring to the south pole of Earth.

Earth's magnetic field is also not perfectly aligned with the planet's rotation; it is tilted at an angle of 11 degrees. It's also not stationary; the magnetic poles are continuously shifting, and indeed, the south magnetic pole (at geographic north) has drifted as much as 1,100 kilometres (684 miles) across the Canadian Arctic over the past four centuries.

It's intriguing to note that despite the vastness of our planet, the magnetic field is actually weaker than a refrigerator magnet. However, this seemingly modest strength is more than enough to shield us from harmful radiation from the Sun and other galactic sources. In fact, it's this very magnetic field that's instrumental in preserving our planet's atmosphere.

Origin of the Earth's Magnetic Field

As already discussed, Earth's magnetic field results from the shifting electric field in the liquid molten iron core. Compared to the surface, the magnetic field at the core is about 50 times more potent.

It's most likely that Earth has had a magnetic field for pretty much the entirety of its 4.5 billion-year lifetime. However, when Earth first formed, it's most likely that the entire core used to be liquid; at the moment, only the outer core is liquid, with the inner core being solid due to the intense pressure. This means that Earth's early magnetism was likely stronger than it is now. We can't be sure exactly how much stronger it is, but it's believed this strong magnetic field helped Earth retain an atmosphere early in its life, in the opposite way that Mars lost its atmosphere as its magnetic field dissipated.

Future of the Earth's Magnetic Field

It's a mystery that even the most brilliant minds are yet to fully unravel-the gradual weakening of Earth's magnetic field. While the exact cause remains elusive, historical records indicate that its intensity has fluctuated over time. Since the pioneering measurement by German mathematician Carl Friedrich Gauss in 1845, it has diminished by about ten per cent.

If the magnetic field drops considerably further, there is a probability the magnetic field could flip. Contrary to popular belief, however, this will not represent the world's end. The magnetic field has been known to flip repeatedly over the last billion years, and life has survived. Therefore, it's not likely that another flip would cause any devastating effects.

The only true danger is if the magnetic field vanishes completely. This could lead to increased exposure to harmful solar radiation, which can have detrimental effects on life on Earth. However, as long as Earth has a liquid core, it will continue to have a magnetic field. Unless you are still around in a couple of billion years when such an event may happen, you have little to fret about.