Magnetic Reversals Part II - Magnetic Reversals Layered lava flows reveal reversals in polarity Magnetic polarity is the direction of magnetic north A

Magnetic Reversals Part II - Magnetic Reversals Layered...

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Magnetic Reversals Layered lava flows reveal reversals in polarity. Magnetic polarity is the direction of magnetic north. A reversed N magnetic pole is near the S geographic pole. Reversals are geologically rapid. Reversals can be used as time markers .
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Radioactivity permits rock absolute age-dating. Geomagnetic reversals have been placed in a time scale. Reversals occur every 500-700 ka (chrons). Shorter durations (~200 ka) = subchrons. Magnetic Reversals
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Sea-Floor Spreading: Proof Reversals in polarity explain magnetic anomalies. Positive anomalies Normal polarity crust. Negative anomalies Reversed polarity crust. Magnetic anomalies are symmetric across a mid- ocean ridge.
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Sea-Floor Spreading: Proof Magnetic anomalies mimic layered lava flows. Magnetic “stripes” form as lava cools at a mid -ocean ridge. Ocean crust spreads away from mid-ocean ridge. Reversals are recorded within the cooled basaltic lava. Sea-floor Spreading is the mechanism of continental drift.
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Sea-Floor Spreading Drilling in the late 1960s recovered crust samples. Ages increase away from the mid-ocean ridge. Ages are “mirror images” across the mid -ocean ridge. Strong supporting evidence for sea-floor spreading.
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Plate Tectonics The paradigm of “How the Earth Works.” Earth’s outer shell is broken into rigid plates that move. Moving plates change the face of planet Earth. A case study of a Scientific Revolution. A powerful idea based on multiple lines of evidence. Allows scientists to predict events and rebuild the past.
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Plate Tectonics Tectonic theory evolved in the 1960s. Previous research provided a strong foundation. Wegener (1915) Evidence supporting continental drift Hess / Dietz (1960) The sea-floor spreading hypothesis.
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  • Spring '08
  • idontknow
  • Plate Tectonics, mid-ocean ridges, plate boundaries, sea-floor spreading

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