Earth’s Magnetic Field ! Flow in the liquid outer core creates the magnetic field. " It is similar to the field produced by a bar magnet. " The magnetic pole is tilted ~11.5° from the axis of rotation. Magnetic Poles ! The magnetic pole moves w.r.t the Earth’s surface. (i.e. Geographic and magnetic poles are not parallel.) " Magnetic poles are located near geographic poles. " Magnetic poles move constantly. The Earth’s Magnetic Field; A compass points to magnetic N, not geographic N. ! The difference between geographic N and magnetic N is called declination. It depends on: " Absolute position of the two poles #Geographic north #Magnetic north " Longitude The Earth’s Magnetic Field; Curved field lines cause a magnetic needle to tilt. ! Angle between magnetic field line and surface of the Earth is called inclination. It depends on: " Latitude Paleomagnetism; Rock magnetism can be measured in the laboratory. ! The study of fossil magnetism is called paleomagnetism. ! 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. ! Iron minerals archive the magnetic signal at formation. ! Hot magma " High Temp—no magnetization #Thermal energy of atoms is very high. #Magnetic dipoles are randomly oriented.
Iron minerals archive the magnetic signal at formation. ! 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. Polar Wandering; ! Layered basalts record magnetic changes over time. ! Inclination and declination indicate change in position. -> Apparent Polar Wandering; 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 -> Polar Wandering; 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. ! These curves align when continents are reassembled. ----Slayt5----- Any substance that flows is a fluid. A solid, liquid or gas can all also be a fluid!! Fluid vs Liquid; Solid Fluid: The asthenosphere +Mesosphere (mantle below lithosphere) Liquid Fluid: The ocean, or the outer core Gas Fluid: The atmosphere! Slides courtesy of Erik Chan, postdoctoral fellow at the McGill Space Institute: I.Electromagnetism; How a generator/motor works: ‣A charge moving through a magnetic field feels a force ‣i.e., a changing magnetic field generates an electric current ‣A moving electric charge (e.g. an electric current) generates a magnetic field II.The Earth’s Dynamo; Earth’s outer core: ‣Liquid iron (a conductor) ‣Convecting to dissipate heat (electric current) ‣Generates magnetic field ‣Shaped in part by Earth’