What is the difference in magnetism between continental and oceanic crust?

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Neither are magnetic in the macroscopic sense that we might be accustomed to (iron doesn't stick to them or anything like that). Their magnetism has more to do with the arrangement of magnetic ores in relation to the Earth's magnetic field.

The Earth's magnetic field is pretty strong, but not...

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Neither are magnetic in the macroscopic sense that we might be accustomed to (iron doesn't stick to them or anything like that). Their magnetism has more to do with the arrangement of magnetic ores in relation to the Earth's magnetic field.

The Earth's magnetic field is pretty strong, but not strong enough to reorient objects at typical energies (you wouldn't see an iron bar on your desk spontaneously reorient). However, at higher temperatures, individual atoms can reposition themselves so they align with the magnetic field, and this is what we see happening at seafloor spreading areas, where new oceanic crust is generated as magma emerges and cools. Additionally, the Earth's magnetic field periodically and unpredictably reverses its polarity, which causes the corresponding orientation of new rock to flip, resulting in the seafloor magnetism looking like a series of magnetic stripes on either side of the spreading center.

Magnetism in continental crust is nowhere near as easy to evaluate; where oceanic crust is almost entirely volcanic, continental crust has a wide variety of rock types, many of them deformed, heated and chemically altered, so that any magnetic information they had when they were laid down has been shifted, obliterated, or covered up by layers of sediment. 

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