Understanding how planet earth works: FinalPaleomagnetism and geomagnetic pole pathsPaleomagnetismoRock magnetism can be measured in the laboratory. oThe study of fossil magnetism is called paleomagnetism.oIron (Fe) minerals in rock preserve information about the magnetic field at the time the rocks formed. Declination and inclination preserved in rocks often vary from present latitude / longitude. Instruments used in paleomagnetism record changes in position.These data are used to trace continental drift.oIron minerals archive the magnetic signalat formation.oHot magmaHigh Temp—no magnetizationThermal energy of atomsis very high.Magnetic dipoles arerandomly oriented.oIron minerals archive the magnetic signalat formation.oCooled magmaLow Temp—permanent magnetizationThermal energy of atoms slows.Dipoles align with Earth’s magnetic field.Magnetic dipoles become frozen in alignment with field.Geomagnetic pole pathsoLayered basalts record magnetic changes over time. oInclination and declination indicate change in position.oPolar wandering paths were initially misinterpreted: Not the signature of a wandering pole on a fixed continentThe signature of a fixed pole on a wandering continent oEach continent had a separate polar wandering path. Now understood to represent that:The location of the magnetic pole is fixed.The continents themselves have moved.oThese curves align when continents are reassembled.oTed Irving of the Geological Survey of Canada is usually credited with this discovery (OJ).Magnetic ReversalsoLayered lava flows reveal reversals in magnetic polarity. The magnetic field sometimes “flips”; we don’t know why. A reversed N magnetic pole is near the S geographic pole. oReversals are geologically rapid, expressed worldwide.