Hazards 2 The Theory of Plate Tectonics

• core: 
  • Rock containing iron and nickel alloys
  • Solid inner core and molten outer core
  • 5000℃
  • primordial heat (from Earth’s formation0
  • Radiogenic heat (radioactive decay of isotopes: uranium-238, thorium-232 and potassium-40)
• mantle:
  • Molten and semi molten rocks
  • Contains elements such as silicon and oxygen
• crust:
  • Lighter elements such as silicon, oxygen, aluminium, potassium and sodium
  • Continental crust: 30-70km thick
  • Oceanic crust: 6-10km thick
• lithosphere: the crust and the rigid upper section of the mantle
• asthenosphere: below the lithosphere and is semi molten on which the plates float and move

The Theory:

• 1912 Alfred Wegener
  • Pangea: the super continent
  • Laurasia and Gondwanaland: Pangea split into these
• Geological evidence:
  • South America and West Africa fit together
  • Striations of rock from Brazil and West Africa that match up
  • Rock sequences in Scotland and East Canada
• Biological evidence:
  • Fossil brachiopods found in Indian limestone and in Australia

Development of the Theory:

• The mid Atlantic ridge suggested that seafloor spreading was occurring
• Iron particles in in the ocean floor are aligned with Earth’s magnetic field, as they solidify it shows the polarity of Earth at…