Magnetic reversals

Dr Humphreys also proposed a test for his model: magnetic reversals should be found in rocks known to have cooled in days or weeks. For example, in a thin lava flow, the outside would cool first, and record Earth’s magnetic field in one direction; the inside would cool later, and record the field in another direction.

Three years after this prediction, leading researchers Robert Coe and Michel Prévot found a thin lava layer that must have cooled within 15 days, and had 90° of reversal recorded continuously in it.9 And it was no fluke — eight years later, they reported an even faster reversal.10 This was staggering news to them and the rest of the evolutionary community, but strong support for Humphreys’ model. See also Dr Humphreys’ online article The Earth’s magnetic field is young.

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Originally posted by LiveFreeOrDie
Since new rock is formed here at a fairly steady pace, they provide an excellent history of the Earth's magnetic field.

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