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We even have a record of ancient Earth’s magnetic fields :) The geological record is pretty amazing indeed!

• jjtheblunt 2y ago
  How is magnetic field history figured out?
  • BWStearns 2y ago
    Basalt on the ocean floor records the magnetic field of the earth from when it cooled. Since it radiates out from midoceanic rifts and the rate of its creation is known, we can use it as a diary of the magnetic field. Iirc we first figured it out during WW2 doing magnetic bathyometry to help ships navigate.
  • CalRobert 2y ago
    https://en.m.wikipedia.org/wiki/Remanence https://en.m.wikipedia.org/wiki/Remanence can get you started! I did horribly in this lab session in college but it was still fun.