Elementary Plate Tectonics

• Evidence for Pangea can be geological, biological, or climatic.
• Geological Evidence:

  • South America and Africa fit together
  • there are matching patterns in the structures of mountains in NE USA and NW Europe
• Biological Evidence:

  • Mesosaurus fossils of the same age were found in South America and Africa, even though the animal couldn't swim long distances
• Climate Evidence:

  • coal is formed in tropical swamps, yet is found all over the world
  • limestone is formed from coral reefs and marine organisms in the tropics, yet it is found everywhere
• Oceanic crust is 10 km deep, but continental crust can reach 70 km in thickness.
• The evidence for sea floor spreading is that oceanic crust has repetitive symmetrical patterns on either side of the mid-ocean ridge. This occurs due to the poles of the Earth inverting every 300,000 years. This causes the charged molecules in the magma to line up facing different directions throughout time. Each side of the ocean is symmetrical showing that the magma solidified in the middle and then was operated by the movement of the plate by convention currents.
• Plate separation:

  1. Rift Valley -> plates separate due to convection currents as they are pulled in opposite directions, the gaber falls into the space created e.g. African plate
  2. New Ocean Basin -> plates continue to move away from each other, so magma comes up and solidifies, forming the oceanic crust e.g Red Sea
  3. Mature Ocean -> large oceanic plate where the ridge is hidden under sediment e.g. Atlantic Ocean
• constructive plate boundary:

  1. convection currents move plates apart (mostly oceanic)
  2. creates a mid-oceanic trench (Rift Valley)
  3. up-welling of magma creates volcanoes
  4. formation of mid-ocean ridge
  5. transform faults