Eli5 The earth has a magnetic field, including because of the metal core, but magnets are demagnetized at high temperature. How is this possible
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Only tangentially related to this question, but the north pole of the earth is a magnetic south pole. Which is obvious once you think about it, but not something you might normally notice.
usually magnets are magnetic because the electricity in them go spin, making a magnetic field
these magnets become not magnets when hot because the electricity doesn’t spin together nicely and becomes chaotic
however, for the earth, even though it’s hot, they still spin together nicely because the hot molten rocks under us are spinning as a whole so in the end, you still got electricity spinning roughly together enough to make a magnetic field
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Magnetism is a fancy word for magic.
Don’t believe me? If water is flowing from a mountain to level ground, why doesn’t it create an ‘aquatic field’ during flow? Because water, while remarkable, is not magic, of course.
So why is it that when electrons behave in, essentially, the same way – seeking equilibrium, that they generate fields of energy? Why is it that earth’s magnetic field doesn’t tear apart all matter on the planet, by ripping electrons to it’s positive pole, and all protons to the negative pole? Why doesn’t that happen when I stick my hand in a magnetic field? Well, because magnetism is magic, of course.
Magnetism is caused my the movement of electrons, ie current. Every electron has a “magnetic moment”. An atom can have a net magnetic field due to the arrangement of its electrons as they orbit the nucleus. A group of atoms, ie a magnet, gets its net magnetic field from large percentages of its atoms having aligned magnetic fields. When a magnet like this is heated the atoms unalign which is why the magnet ceases to be a magnet at temperature.
The earths core is essentially spinning molten metal. Metals have a lot of electrons. Which means moving electrons. Which means current. Which means magnetic field.
The loss of magnetic properties is called the curie effect. The temperature at which it happens is called the curie point. Above the Curie temperature, the atoms are excited, and the spin orientations become randomized and that is what makes materials lose their magnetic properties. Minidisc is a magneto-optical media. Data gets recorded to it by using the curie effect.
The magnetic loss is not permanent. Once this cool down the magnetism returns.
Earth’s Outer Core is heated by the first events from the solar systems’ history, and by friction heating, caused by denser/colder material sinking to the bottom, and also by decay of radioactive isotopes. EOC also suffers from density variation throughtout its depth, denser stuff at the bottom, lighter on top. This sets up the conditions for an naturally occuring electric generator. Convection currents are transformed into electromagnetic ones by heating up the iron and electric currents are induced by earth’s magnetic field. Those electric currents have their own magnetic field. And thus the process is self sustained as long as there is heat being generated in large enough quantities.
The earths magnetic field isn’t created by the iron in the core being magnetic, it’s created by the way if flows around inside the core.
This has secondary effects or magnetising some of the iron, but let’s forget about this.
The mag Eric field is mostly from the movement of the iron.
Magnetic fields are generated by charged particles with angular momentum. Angular momentum comes from two different places.
1. Orbital angular momentum, which arises when a particle moves in a loop.
2. Spin angular momentum. This is a quantum property of particles which is intrinsic and depends on the kind of particle.
Permanent magnets (like cobalt) arise when all of the particles in a metal’s spin angular momentum line up with each other, creating a large net angular momentum and therefore magnetic field (dipole moment). When the temperature is high, all the spins jiggle around in random directions, and they cancel each other out, destroying the magnetism. The Earth does not work like this. It’s magnetic field arises because of orbital angular momentum – the Earth is spinning, as are all of the charged particles in the mantle, giving a large magnetic field.
Oh this is a super cool question! You are indeed correct, bar magnets and those like it can not do hot temps, they fail. But that’s not how the Earth’s magnetic sphere operates. Here on the surface we often use stable magnets to generate electricity. This works on a principle that moving magnetic fields through each other creates electric current. But this is also true in reverse. Moving electric fields can cause magnetic fields.
So the Earth’s core is iron nickle… stuff, we’re not 100% but it’s metal and it’s solid and it’s hot AF. This basically only operates as an antenna. The outer core, however, is liquid and it moves, a lot, moving differently charged metals next to each other causes electricity to generate. And a side effect of generating electrical charge is you also create magnetic fields. This is then focused to the poles because of the axis of rotation and the rotation itself. The sciency name for this is called the “Dynamo Effect” which sounds like a stupid made up sci-fi hand wave, but that’s the name, they didn’t consult me when they named it.
But that’s the gist. The earth is basically accidentally a magnet, it’s a side effect of a geological process of having a liquid metal outer core that’s just hot enough and under just enough pressure for this to work.
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