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Cause of Earth's magnetic field
We actually don't know how Earth's magnetic field originates! The best contender explanation we have is the following.
The Earth has a liquid core. This core is made up of two parts, but all we care about in this article is the outer part, which is a molten outer core made entirely of iron. This iron is an electric conductor, so currents can flow through the outer core. It is thought that these electric currents are the cause of the Earth's magnetic field, but the details are not yet known to science.
Earth's magnetic field description
The magnetic field strength of the Earth's magnetic field may be smaller than you expect. Magnetic field strength is measured in Tesla (\(\mathrm{T}\)), and the Earth's magnetic field strength is in the range of 25 to 65 \(\mu\mathrm{T}\). For reference, the magnetic field strength of a standard fridge magnet is about 1 \(\mathrm{mT}\). That's about 40 times stronger!
The shape of the Earth's magnetic field may seem familiar to you if you've seen the magnetic field of a bar magnet before. Like a bar magnet, magnetic field lines emerge from the magnetic north pole, and curve back and directly into the magnetic south pole, encasing the entirety of the planet in the process.
The magnetic field that covers the entire planet is called the magnetosphere. The magnetosphere is incredibly important to the safety of our planet for one very big reason. There are many dangerous things in space, many of which are more than capable of travelling to our planet and causing a massive amount of damage to both us and the environment. The magnetosphere protects us from a lot of these things, such as solar winds, which come from the sun as a form of Radiation that could injure us greatly as well as damage all the electronics on the planet. Our magnetosphere is able to repel these harmful Particles.
Diagram of the Earth's magnetic field
The image below shows what our planet's magnetic field looks like. It behaves almost exactly like a regular bar magnet.
Fig. 1: The Earth's magnetic field lines.
It's essential to know that the North Pole of the Earth is actually the magnetic south pole, which is why in the above image the arrows on the magnetic field lines are in the opposite direction as you are used to!
Did you know that auroras are caused by the Sun? Storms on the Sun throw charged Particles off to every corner of space, including our planet. When these Particles come in contact with the Earth, they hit Particles in the atmosphere.
So what does this have to do with the Earth’s magnetic field? Well, once these charged particles are close enough, the magnetic field pulls them towards the north and south poles. As they travel closer and closer to the Earth, they collide with atoms in our atmosphere, increasing the energy of those atoms. These atoms are now unstable and will get rid of their energy by emitting photons, which we can see as light: these are the auroras. The magnetic field of the Earth causes the auroras to only be visible close to the Earth's magnetic poles.
Fig. 2: An example of an aurora. The aurora is a result of particles from the Sun being redirected to the Earth's poles by Earth's magnetic field and colliding with the particles in the atmosphere.
Compasses and Earth's magnetic field
A compass is one of the most useful tools you can have when you need to know where you're going. A compass shows you which way north, south, east, and west are. However, beyond the fact that it uses magnetism to tell you where these directions are, most people don't know exactly how they work.
A defining feature of magnets is the fact that they all have a needle with a north pole and a south pole. All north poles attract south poles, and all south poles attract north poles. The metal needle on a compass is a magnet and is therefore affected by the magnetic field of the Earth. It will point its north end to the magnetic south pole of the Earth at all times.
This means that the North Pole as we know it is magnetically speaking a south-seeking, or south pole!
Fig. 3: A standard compass. The north pole of the compass needle points towards the Earth's south-seeking pole, which is the magnetic North Pole.
The Earth technically has two north poles! The 'true' or 'geographic' North Pole is right at the geographic top of the planet, and the magnetic North Pole, of which the location is constantly changing, is right at the magnetic top of the Earth's magnetic field. When a compass needle is pointed north, it is pointing to the magnetic North Pole (which is a south pole) and not to the geographic North Pole you see on maps and globes! This difference is very important if you are close to one of the poles, as the difference in the direction of the geographic and the magnetic poles will be large there.
The relationship between magnets and the Earth's own magnetic field was first discovered in 1600 by William Gilbert, an English physicist. It wasn't until 1840 that it was realized that the source of this field comes from the centre of the Earth, by Carl Gauss.
Earth's magnetic field flip
The magnetic north and south poles of the Earth will not stay in the same location forever. It is known to us that after a period of about 300,000 years on average, these magnetic poles will swap places entirely. Thankfully, during the flipping of the poles the magnetosphere never fully disappears, so we still have a degree of protection from the dangers of space. However, the magnetic field will noticeably weaken during this event. This can cause many problems, including with navigation.
Earth as a Big Magnet - Key takeaways
- The Earth is a big magnet, probably due to electric currents running through the molten iron outer core inside the planet.
- The Electric Current in the Earth generates the magnetosphere, a giant magnetic field that surrounds the entire planet.
- The magnetosphere protects the planet from harmful Radiation such as solar winds.
- The magnetic poles of the planet will flip over a long period of time.
- Compasses are made so that the north pole of the compass needle is always attracted to the magnetic North Pole of the Earth while it is in Earth's magnetic field. This makes the magnetic North Pole a south-seeking, or South Pole!
References
- Fig. 1- Earth's magnetic field (https://commons.wikimedia.org/wiki/File:VFPt_Earths_Magnetic_Field_Confusion_overlay.svg) by MikeRun (https://commons.wikimedia.org/wiki/User_talk:MikeRun) is licensed by CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/deed.en)
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Frequently Asked Questions about Earth's Magnetic Field
Is the Earth a very big magnet?
The Earth generates a large magnetic field, and this makes it such that we can effectively call the Earth a magnet.
Who proposed that Earth is a big magnet?
The Earth was first theorised to be a big magnet by William Gilbert in the year 1600.
What evidence shows that Earth is a huge magnet?
Evidence that the Earth is a huge magnet includes the behaviour of the auroras and the behaviour of compass needles.
How is the aurora related to the earth's magnetic field?
Auroras are created by the Sun emitting large amounts of particles during events known as coronal mass ejections. Once these particles reach the Earth, they interact with the magnetosphere to cause auroras to appear in the sky around the Earth's magnetic poles.
What makes the Earth magnetic?
The Earth is magnetic due to the electric currents that run through the outer core of molten iron within the Earth's core. Currents running in loops generate a magnetic field.
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