Earths Magnetic Field Flow in the liquid outer core creates a magnetic field It

Earths magnetic field flow in the liquid outer core

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Earth’s Magnetic Field - Flow in the liquid outer core creates a magnetic field - It is similar to the field produced by a bar magnet - The magnetic pole is tilted approximately 11.5 degrees from the axis of rotation - A compass points to the magnetic North, not geographic north. - The difference between geographic North and magnetic North is called declination - Angle between magnetic field line and surface of the earth is called inclination Magnetic Poles - The magnetic poles move with the earth’s rotation axis - Geographic and magnetic poles are not parallel - Magnetic poles are located near the geographic poles - Magnetic poles move constantly 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. o Declination and inclination preserved in rocks often vary from present latitude/longitude o Instruments used in paleomagnetism record changes in position o These data are used to trace continental drift - Iron minerals archive the magnetic signal at formation - Hot magma has randomly oriented magnetic poles - Cooled magma: the magnetic dipoles become frozen in alignment with field because the thermal energy of the atoms is slow. 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 on a fixed continent - It is actually the continent that is moving not the poles. - The location of the magnetic pole is fixed. Sea-floor Bathymetry from Echo-Sounding
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- Sonar waves reflect from the bottom - Sea-floor maps created by ships - There are deep sea trenches, oceanic islands, seamounts and guyots - Heat flow = evidence for mantle upwelling - Basalt is an igneous rock formed from mid-ocean ridges Earthquakes and the oceanic crust - Earthquakes in the oceanic crust is limited to: o Parts of oceanic fracture zones o Mid ocean ridges axes o Deep ocean trenches - Earthquakes are happening along the same boundary that were found on the ocean floor - This all led to Hess’ concept of sea-floor spreading (explaining continental drift) - The ocean floor is formed at the ridges, drifts away from them on both sides, then plunges into the mantle at the trenches - The seafloor was viewed as a conveyor belt for marine material Evidence of seafloor spreading - Magnetism in sea-floor rocks varies father from mid ocean ridges - Stripes of positive and negative magnetism - The magnetism was recorded in the sea basalt - Magnetic anomaly = difference between the expected strength of the Earth’s magnetic field at a certain location and the actual measured strength - The magnetic poles have reversed many times - The magnetic data is symmetric on either side of the mid ocean ridges Sea floor spreading - There is new material coming out from mid ocean ridges and then that material moves away and then new material comes out.
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