Tectonic Plate Theories

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  • Plate Tectonic Theorys
    • Alfred Wegener
      • super continent 'Pangaea' split into two continents of Laurasia and Gondwanaland. theses continents where further split into the land masses we know today as continents.
      • geological evidence that supports the theory
        • south america and african shapes of continents fit together
        • glaciation of the late carboniferous period, where deposits form which were found in South America, Antarctica and India. they must have been formed together and then moved appart
        • rock sequences in northern Scotland closely agree with those found in eastern Canada - same conditions in one location
      • biological evidence
        • fossil brachiopods found in Indian Limestones are comparable with similar fossils in Australia
        • fossil remains of the Mesosaurus are found in both South America and South Africa - it is unlikely that the same reptile could have developed in both areas or that it could have migrated across the Atlantic
        • the fossilised remains of a plant which existed when coal was being formed have been located only in India and Antarctica
    • Sea floor spreading
      • the Mid-Atlantic Ridge is a constructive plate boundary, where the two plates are moving away from one another
        • As Crust is being created here, somewhere else it mustbe being destroyed, evidence of this is ocean trenches where  large areas of ocean floor are being pulled downwards
      • when the Earth's magnetic field changes the alignment of the iron particles erupting from the ocean floor also changed, to face the new magnetic 'North'.
        • Palaeomagnetism
      • the ocean crust gets older with distance from the mid-oceanic ridge.

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