Disclaimer: no Geodude was damaged during this study. For those who don’t know, Earth is a magnet. A really big one, so we are surrounded by a massive magnetic field that works as a protector shield against radiation from the Sun and other weird outter space things. As a magnet, it has two poles. But do you know that what we call North Pole is actually the magnetic South Pole and viceversa? If you follow a compass you would think that it is pointing to the North. But compasses are aligned with the field lines (Faraday’s idea, who was a great scientist without scientific formation, which is cool), and the field lines are a map that tell us how to go from the North to the South of a magnetic field, apart of many other things (look at the figure). So poles are reversed. And rocks have been secretly telling us that it has been reversing for so long.

In the Mid-Atlantic Ridge, two tectonic plates are slowly separating. As a result, melted rock under the lithosphere, called magma, reaches the surface and solidifies under the ocean, creating new lithosphere (Icelandic vulcanism). Magnetic things are magnetic because the spin of their electrons are coherently aligned, contributing to create this magnetism. But in some rocks, spins are usually randomly oriented, neutralizing between themselves and making the total contribution to create magnetism zero. However, under some temperature conditions, these spins can be forced to align with an external magnetic field (Paramagnetism and Curie’s Law). Casually, when this rocks are created, they reach that temperature, so their spins aligne with the external magnetic field at that moment (the Earth’s one). When the conditions disappear the magnetization remains in time (Ferromagnetism and Remanent Magnetism). Nowadays, we can take those rocks and determine when they were created and where was pointing the external magnetic field at that moment. (Another figure). By the way, this is the explanation of Geodude evolutive line becoming electric type in the new Pokemon games.

This is tectonic plates movement demonstrating itself. And rocks use magnetism to explain us about it, like if they were an open book of Earth’s history. In the future, it may occur again, maybe sooner than later, looking at the periodic behaviour of these reversals. Is our telecommuncation based world prepared for this?

Header figure: Paramagnetic and ferromagnetic geodudes

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