[fiscally_right]

People noted that while rocks on Earth were magnetized in a disordered way, the sea bottom was magnetized in long strips. Larry Morley (whose article was regarded so speculative that journals would not publish it) and then Matthews and Vine (who managed to publish) suggested that molten rock was spreading out like a conveyer belt from volcanic cracks in the middle of the ocean floor, e.g. the one in the middle of the Atlantic (Azores islands sit on it). Or rather like 2 belts, one moving towards Europe, one towards America, carrying on them the continental plates, so that Europe and America gradually drift apart. As each belt comes out of the crack, its lava solidifes to basalt, causing it to become magnetized, and when the field reverses, its magnetization reverses too. So the bottom of the ocean records the field like the tape of a tape recorder, containing perhaps 50 million years of record.

[Indie]

Excellent nutshell of plate tectonics theory. One of my Geology profs used to joke about the earth reversing it's magnetism. He stated that would kill us all by allowing radiation through from the sun. If that didn't do it, the sun turning into a brown darf would.
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