The Earth's magnetic field is like the magnetic field of a giant permanent magnet tilted 11 degrees to its axis of rotation. But there is a nuance here, the essence of which is that the Curie temperature for iron is only 770 ° C, while the temperature of the Earth's iron core is much higher, and only on its surface is about 6000 ° C. At this temperature, our magnet would not have been able to keep its magnetization. This means that since the core of our planet is not magnetic, earthly magnetism has a different nature. So where does the earth's magnetic field come from?
As you know, magnetic fields surround electric currents, so there is every reason to assume that currents circulating in the molten metal core are the source of the earth's magnetic field. The shape of the Earth's magnetic field is indeed similar to the magnetic field of a current loop.
The magnitude of the magnetic field measured on the Earth's surface is about half a Gaussian, while the lines of force seem to go out of the planet from the south pole and enter its north pole. At the same time, over the entire surface of the planet, the magnetic induction varies from 0.3 to 0.6 Gauss.
In practice, the presence of a magnetic field at the Earth is explained by the dynamo effect arising from the current circulating in its core, but this magnetic field is not always constant in direction. Rock samples taken in the same places, but having different ages, differ in the direction of magnetization. Geologists report that over the past 71 million years, the Earth's magnetic field has unfolded 171 times!
Although the dynamo effect has not been studied in detail, the Earth's rotation certainly plays an important role in generating currents that are believed to be the source of the Earth's magnetic field.
The probe "Mariner 2", which explored Venus, found that Venus does not have such a magnetic field, although its core, as well as the core of the Earth, contains enough iron.
The answer is that the period of rotation of Venus around its axis is 243 days on Earth, that is, the dynamo generator of Venus rotates 243 times slower, and this is not enough to produce a real dynamo effect.
Interacting with particles of the solar wind, the Earth's magnetic field creates conditions for the appearance of the so-called polar lights near the poles.
The north side of the compass needle is the magnetic north pole, which is always oriented towards the geographic north pole, which is practically the magnetic south pole. After all, as you know, opposite magnetic poles are mutually attracted.
However, the simple question is, "how does the earth get its magnetic field?" - still does not have a definite answer. It is clear that the generation of a magnetic field is associated with the rotation of the planet around its axis, because Venus with a similar core composition, but rotating 243 times slower, does not have a measurable magnetic field.
It seems plausible that the rotation of the liquid of the metal core, which makes up the bulk of this core, creates a picture of a rotating conductor, creating a dynamo effect and working like an electric generator.
Convection in the liquid in the outer part of the core leads to its circulation in relation to the Earth. This means that the electrically conductive material moves relative to the magnetic field. If it turns out to be charged due to friction between the layers in the core, then the effect of a coil with a current is quite possible. Such a current is quite capable of supporting the earth's magnetic field. Large-scale computer models confirm the reality of this theory.
In the 1950s, as part of the Cold War strategy, US Navy vessels towed sensitive magnetometers along the ocean floor, while they were looking for a way to detect submarines. In the course of observations, it turned out that the Earth's magnetic field fluctuates within 10% in relation to the magnetism of the seabed rocks directly, which had the opposite direction of magnetization. The result was a picture of the reversals that took place up to 4 million years ago, this was calculated by the potassium-argon archaeological method.
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