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Scientists know that some minerals have magnetic
properties. In molten rock the magnetic properties line up in relation
to Earth’s magnetic poles. When the rocks harden, a permanent
record of the Earth’s magnetic poles are revealed. Scientists
discovered that on each side of the midocean ridges there were magnetic
stripes. The stripes showed that at several times in Earth’s history,
the magnetic poles have reversed. The stripes matched up on each side of
the midocean ridge. This discovery added more evidence to support
ocean-floor spreading.
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