Glossary of earthquake terms
(Image from "This Dynamic Earth: The Story
of Plate Tectonics")
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Magnetic polarity
reversal
A magnetic
polarity reversal is a change of the earth's magnetic field
to the opposite polarity. This has occurred at irregular
intervals during geologic time. Polarity reversals can be
preserved in sequences of magnetized rocks and compared
with standard polarity-change time scales to estimate geologic
ages of the rocks. Rocks created along the oceanic
spreading ridges commonly preserve this pattern of polarity
reversals as they cool, and this pattern can be used to
determine the rate of ocean ridge spreading. The reversal
patterns recorded in the rocks are termed sea-floor magnetic
lineaments.
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