Final notes.docx - Understanding how planet earth works Final Paleomagnetism and geomagnetic pole paths Paleomagnetism o Rock magnetism can be measured

Final notes.docx - Understanding how planet earth works...

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Understanding how planet earth works: Final Paleomagnetism and geomagnetic pole paths Paleomagnetism o Rock magnetism can be measured in the laboratory. o The study of fossil magnetism is called paleomagnetism. o Iron (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. o Iron minerals archive the magnetic signal at formation. o Hot magma High Temp—no magnetization Thermal energy of atoms is very high. Magnetic dipoles are randomly oriented. o Iron minerals archive the magnetic signal at formation. o Cooled magma Low Temp—permanent magnetization Thermal energy of atoms slows. Dipoles align with Earth’s magnetic field. Magnetic dipoles become frozen in alignment with field. Geomagnetic pole paths o Layered basalts record magnetic changes over time. o Inclination and declination indicate change in position. o Polar wandering paths were initially misinterpreted: Not the signature of a wandering pole on a fixed continent The signature of a fixed pole on a wandering continent o Each 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. o These curves align when continents are reassembled. o Ted Irving of the Geological Survey of Canada is usually credited with this discovery (OJ). Magnetic Reversals o Layered 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. o Reversals are geologically rapid, expressed worldwide.
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