Structure of the Earth

Structure of the Earth

1. Basic Structure

   • Crust
     • Solid
     • Composition
       • 46.6% Oxygen
       • 27.7% Silicon
       • Thickness
         • Max. 70km
         • Under land 30km
         • Under oceans 5km
   • Mantle
     • Solid
     • Semi-solid
     • Extends from 20km to 2900km
       • Half way to the centre of the Earth
     • Composition
       • Fe
       • Mg
       • Al
       • Si
       • O
     • Temperature
       • 100ºC at top
       • 3700ºC at bottom
       • Caused by isotope decay
   • Outer Core
     • Liquid
     • 2300km thick
     • Molten nickel-iron alloy
     • Controls magnetic field
   • Inner Core
     • Solid
     • 1200km thick
     • Solid iron
     • 7000K at centre
   • Lithosphere
     • Crust & Upper Mantle
     • Solid
     • >80km thick
     • Thinner under oceans
     • Floats on lower mantle
     • Divided up into plates

2. Plate Tectonics

   • First Evidence
     • 1912
       • Shape of Africa & Americas
       • Fossil evidence
       • Thought to be driven by centrifugal force
     • 1929
       • Thought to be caused by convection in rocks
       • Evidence for sea floor spreading
       • Magnetic stripes
   • Plate Boundaries
     • Transform boundaries
       • Two plates sliding along each other
       • San Andreas fault line
     • Convergence boundary
       • Two plates moving towards each other
       • Creates a mountain chain and volcanoes
       • Can be of equal or unequal density
         • If density is unequal one plate rises above the other
       • Andes
       • Himalayas
     • Divergent boundary
       • Plates move apart
       • Mid-Atlantic ridge
       • African rift valley
     • Hot spots
       • Plumes of hot magma breaking the surface of the crust
       • Hawii
   • Continental Drift
     • Rodina
       • Pangaea
         • Gondwana
           • Africa, South America, Antarctica, India, Australia
         • Larussia
           • North America, Eastern Europe, Western Europe, Siberia

3. Volcanoes

   • Stromboli eruptions
     • Intermittent explosion or fountaining of basaltic lava
     • Single vent or crater
     • Releases volcanic gases
     • Occur every few minutes or so
     • Mt Etna 2002
   • Hawiian eruptions
     • Highly fluid lava flows
     • Quiet
     • several vents
     • Gradually builds up to a shield volcano
   • Vulcanian eruptions
     • Vulcano off the coast of Italy
     • Strick magma plugs up the central vent
     • Magmatic gas builds up pressure
     • Blasts magma and volcanic dust
   • Peleean eruptions
     • Violent explossions
     • Glowing clouds of hot ash and dust
     • Volcano blows apart

4. Seismology

   • Study of earthquakes
   • Useful for determining the structure of the Earth
     • Time of arrival indicates what material waves have passed through
   • Seismic waves from earthquake pass through the Earth
     • P-Waves
       • Primary waves
       • Compression waves
       • Can pass through solids and liquids
       • Get faster in more dense media
       • Faster
     • S-Waves
       • Secondary waves
       • Shear waves
       • Can pass through solids but not liquids
       • Get faster in more dense media
       • Slower
     • Measured with a seismograph
     • Refraction of waves
       • When passing from a low to high velocity medium, waves get bent
       • Creation of shadow zones