Lecture 4 - Plate boundaries and their Earthquakes

Lecture 4 - Plate boundaries and their Earthquakes -...

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Evidence for Plate Tectonics Evidence for Plate Tectonics Figure 2-19
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Evidence for Plate Tectonics Evidence for Plate Tectonics Magnetic patterns on sea floors Earthquake epicenters and volcanoes map out major plate boundaries Deep ocean trenches Youngest ocean floor rocks are just formed – extremely young (0 million years old) Oldest rocks on ocean floors are no more than ~200 million years old Fit of the continents
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Rocks that formed during a time of switched ( reverse ) magnetic polarity were magnetized with magnetic north pointing south When lava cools to form rock, iron atoms become magnetized in direction of Earth’s magnetic field Direction of Earth’s magnetic field switches – magnetic north moves to south pole and magnetic south moves to north pole – from time to time Rocks that form today are magnetized with magnetic north pointing north ( normal ) magnetic polarity Earth’s Magnetic Earth’s Magnetic Field Polarity Field Polarity Figure 2-4
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Magnetic Pattern of Magnetic Pattern of Ocean Floors Ocean Floors Magnetometer readings of ocean floor (to look for submarines during WWII) easily picked up difference between normally magnetized rocks and reverse magnetized rocks Ocean floor is striped by parallel bands
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Lecture 4 - Plate boundaries and their Earthquakes -...

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