ESC 2200C Lecture 7: ESC1000 Notes September 20th
30 Sep 2016
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Magnetism in sea-floor rocks varies farther from mor: stripes of positive (stronger) and negative (weaker) magnetic intensity, recorded in sea-floor basalts. Magnetic field sometimes flips : reason unknown, a reversed n magnetic pole is near the s geographic pole, geologically rapid. A magnetic reversal time scale has been assembled: reversals occur at uneven intervals, chrons: longer intervals, subchrons: shorter intervals, named for scientists. Polarity reversals explain magnetic anomaly stripes on sea floor. Magnetic polarity reversals are imprinted in sea-floor rock when magma solidifies at the ridge. Possible to determine rates of sea-floor spreading: mid-atlantic ridge ~2 cm/yr, v=45km/4. 5 m, =4,500,000cm/4,500,000 years, =1cm/yr. East pacific rise ~ 10 cm/yr: v=225km/4. 5 m, =22,500,000cm/4,500,000 years, =5 cm/yr. Deep-sea drilling in the 1960s: drilled a series of holes moving away from the mid-atlantic ridge. Plate tectonics: the explanation of how earth works . Earth"s outer shell is broken into rigid plates that move. Moving plates change the face of planet earth.
