ERSC 3P12 Lecture Notes - Lecture 10: Magnetite, Outer Core, Archean
22 May 2016
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Document Summary
Marine magnetic anomalies result of sea-floor spreading. The age of oceanic crust varies with location. The youngest crust lies along a mid-ocean ridge, and the oldest along the coasts of continents. Here, the different color stripes correspond to different ages of oceanic crust. Marine magnetic anomalies are stripes representing alternating bands of oceanic crust that differ in the measured strength of the magnetic field above them. Stronger fields are measured over crust with normal polarity, while weaker fields are measured over crust with reversed polarity. The rock of oceanic crust preserves a record of the earth"s magnetic polarity at the time the crust formed. Eventually, a symmetrical pattern of polarity stripes develops. Marine sediments overlying crust have a vertical magnetic record that mirrors the horizontal record of the basaltic sea floor. High-precision independent dating by milankovitch cycles (astrochronology) only really good back to miocene. Rock evidence for magnetic polarity reversals 3 billion years ago in.
