Lecture 21 Mar 19 2008 Paleomag and seafloor spreading

Lecture 21 Mar 19 2008 Paleomag and seafloor spreading -...

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Another line of evidence about Earth’s interior comes from studying its magnetism. Earth’s outer core generates a magnetic field as a result of the movement of liquid iron in the outer core.
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When lava cools and solidifies, any magnetic minerals that form become magnetized in the direction of the prevailing magnetic field. Earth’s magnetic field in the past was sometimes the reverse polarity of the present field. Rocks record the past magnetic fields on Earth.
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If layers of lava can also be dated, the magnetic history of Earth can be tied to specific dates. It is not known what causes the erratic changes in the polarity of Earth’s magnetic field, but the magnetic reversals are clear in the paleomagnetism record. Epochs of magnetic dominance last about ½ million years with some shorter transient reversals.
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Mapping of the ocean floor – 2/3 of the surface of Earth -- was critical to understanding a dynamic Earth. In 1855, a bathymetric chart published by U.S. Navy Lieutenant Matthew Maury revealed the first evidence of underwater mountains in the central Atlantic (which he called "Middle Ground").
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the East Pacific Rise at 9°N. "Warm" colors (yellow to red) indicate the ridge rising above the seafloor, and the "cool" colors (green to blue) represent lower elevations. Rising 4.5 km
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Lecture 21 Mar 19 2008 Paleomag and seafloor spreading -...

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