What Causes the Earth's Magnetic Field?

Last Updated May 29, 2023 by . First Published in 2019.

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.

Before we will be able to know the way Earth's magnetic field works, we need to first have a fundamental understanding of magnetism. Magnetic fields are formed when electrical charges move through magnetic materials like iron.

The direction of magnetic field lines represented by iron filings sprinkled on paper placed above a bar magnet.
The direction of magnetic field lines represented by iron filings sprinkled on paper placed above a bar magnet. 

Any magnetised material is bipolar, which means that 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 around 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 our planet's magnetic field is induced by a circulating electric current at the core. 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.

Schematic illustration of the invisible magnetic field lines generated by the Earth, represented as a dipole magnet field.
Schematic illustration of the invisible magnetic field lines generated by the Earth, represented as a dipole magnet field. 

Earth's magnetic field is also not perfectly aligned with the rotation of the planet, instead of being 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.

Interestingly, though, despite the size of Earth, the magnetic field is weaker than a refrigerator magnet. However, that is nonetheless sufficient to give protection to us from damaging radiation from the Sun and elsewhere in the galaxy and is helping our planet retain its atmosphere.

Origin of the Earth's Magnetic Field

As already discussed, Earth's magnetic field is the result of 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. Exactly how much stronger we can't be sure, but it's believed this strong magnetic field helped Earth retain an atmosphere early in its life, in the opposite way that Mars has lost its atmosphere as its magnetic field has dissipated.

Future of the Earth's Magnetic Field

Earth's magnetic field is weakening; however, the actual explanation for why is poorly understood. However, this is no cause for concern; records suggest it decreases and increases in intensity relatively frequently. Since German mathematician Carl Friedrich Gauss first measured its strength in 1845, it has dropped 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 end of the world. The magnetic field has been known to flip repeatedly over the last billion years, and life has survived. Therefore it's not likely another flip would cause any devastating effects.

The only true danger is that if the magnetic field were to vanish totally. As long as Earth has a liquid core, though, 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 not got a lot to fret about.

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