Apparent Polar WanderThis image shows one of the fundamental techniques geologists use to reconstruc

Apparent Polar WanderThis image shows one of the fundamental techniques geologists use to reconstruct the motion of plates on Earth. These plots are called “apparent polar wander” plots.Certain rocks contain magnetic minerals, like the mineral magnetite. When these minerals either grow or move around freely (like in flowing water) they align themselves relative to the Earth’s magnetic field. A rock formed in the presence of a magnetic field will wind up with its own magnetic field that points towards the north/south pole at the time it forms.If 2 continents are joined together, 2 rocks formed on those continents at the same time will point to the same North Pole. But the trick for geologists is…what happens if the continents move after the rocks form?Once a rock is formed, the magnetic field is (mostly) locked in. If a scientist measures the magnetic field in rocks across time, that paleomagneticist (also sometimes nicknamed paleomagicians) will be able to see how the magnetic pole moves relative to the continent.Of course, the North Pole isn’t really what is moving, the continent itself is moving – hence the name “apparent polar wander”. The North Pole recorded by the rocks seems to change because the rocks themselves move relative to the North Pole.Finally, go back to our case of 2 rocks forming on 2 continents that are together at one time and rift apart later. Once the continents separate, their rocks will record different magnetic poles as a result of the continental motion, but the tracks of the rocks can be treated like a jigsaw puzzle. In the 2nd image here the apparent polar wander paths from North America and Europe have been altered by assuming that the continents used to be joined together; if you make the assumption that the Atlantic Ocean once closed, suddenly the two curves plot on top of each other for the time when the continents were joined!These kinds of paths are one of the key ways plate motions over time have been reconstructed.-JBBImage credit: Marshak Essentials of Geology textbook, licensed to me for teaching purposes -- source link
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