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The earths magnetic field is believed to have "changed direction" during the earth's formation could you state one piece of evidence used to support this theory
It's not just during the Earth's formation. There have been many changes in the magnetic field direction, and we seem possibly to be heading for another one. The different magnetic layers are present in layers of slightly magnetized rocks, which can be dated by standard methods.
One of the common methods is looking at rocks which are formed in the spreading parts of the ocean floor. The tectonic plates spread apart at the seams in the middles of the oceans at a remarkably constant rates. By looking at the relative orientations of the magnetization of these rocks as a function of where they are found, a history of the Earth's magnetic field can be determined.
(republished on 07/13/06)
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