Structure Of The Earth


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Structure Of The Earth

  1. 1. MOVEMENT AND CHANGE Movements in the Earth
  2. 2. Structure of the Earth
  3. 3. Structure of the Earth <ul><li>We live on the thin, solid crust . </li></ul><ul><li>The mantle is made of hot rock. It extends half way to the centre of the Earth. </li></ul><ul><li>The core is very dense because it is made of iron and nickle. </li></ul>
  4. 4. Structure of the Earth <ul><li>The outer core is molten (liquid) . The inner core is solid. </li></ul>
  5. 5. Structure of the Earth <ul><li>How do we know what the Earth is like inside? </li></ul><ul><li>The answer is that we make use of Earthquakes. </li></ul>
  6. 6. Structure of the Earth <ul><li>An earthquake sends out strong vibrations, called seismic waves . </li></ul><ul><li>These travel from one side of the Earth to the other and can be detected by seismometers. </li></ul>
  7. 7. Structure of the Earth <ul><li>During an earthquake, seismic waves are produced. </li></ul><ul><li>These can be recorded on seismometers. </li></ul>
  8. 8. Structure of the Earth <ul><li>This picture shows the basic idea behind a seismometer. </li></ul><ul><li>They are very sensitive and can even detect atomic explosions from the other side of the world. </li></ul>
  9. 9. Structure of the Earth <ul><li>This is a seismograph and shows the trace produced by a major earthquake. </li></ul>
  10. 10. Structure of the Earth <ul><li>There are two types of seismic waves and it is the difference between these two waves that tells us about the internal structure of the Earth. </li></ul>
  11. 11. Seismic Waves <ul><li>There are two types of waves caused by earthquakes. </li></ul><ul><li>P waves (or primary waves): These are detected first by seismometers because they travel faster than S waves. </li></ul><ul><li>They travel as longitudinal waves. </li></ul>
  12. 12. Longitudinal waves (P waves)
  13. 13. Seismic Waves <ul><li>S waves (or secondary waves): These travel more slowly. </li></ul><ul><li>They travel as transverse waves. </li></ul>
  14. 14. Transverse waves (S waves)
  15. 15. Seismic Waves <ul><li>BOTH P and S waves can travel through solid materials, but transverse waves, S waves, can not travel through a liquid. </li></ul><ul><li>Transverse waves can travel along a liquid surface. </li></ul>
  16. 17. Seismic Waves <ul><li>When an earthquake occurs, P and S waves travel through the Earth. </li></ul><ul><li>They travel on curved paths as they speed up as they go. </li></ul>
  17. 19. <ul><li>P waves are partly reflected and partly refracted. </li></ul><ul><li>S waves are totally reflected; they cannot travel through the liquid core. </li></ul>
  18. 21. <ul><li>Seismometers around the world detect the waves. </li></ul><ul><li>The fact that S waves are not detected on the far side of the Earth from earthquakes give evidence that part of the Earth’s core is liquid. </li></ul>
  20. 23. <ul><li>The outer layer of the Earth made of the crust and upper mantle is called the lithosphere . </li></ul><ul><li>The lithosphere is arranged in plates which cover the Earth. </li></ul><ul><li>Earthquakes and volcanoes occur at the edges of the plates. </li></ul>
  21. 25. Why do the plates move? <ul><li>The hot mantle is heated by radioactive decay in the centre of the Earth. </li></ul><ul><li>This heat cause the liquid magma within the Earth to move (by convection currents) </li></ul><ul><li>It is these huge convection currents which cause the plates to move. </li></ul>
  22. 26. When plates move apart <ul><li>When plates move apart a crack appears between them. </li></ul><ul><li>Molten magma flows from the mantle into the crack. </li></ul><ul><li>This is seen as volcanic activity. </li></ul>
  23. 27. When plates move apart <ul><li>Most of this volcanic activity occurs hidden from view in the depths of the oceans. </li></ul>
  24. 28. When plates come together <ul><li>When two plates collide, one plate will be forced beneath another plate. </li></ul><ul><li>Usually the denser oceanic crust is forced under the less dense continental crust </li></ul>
  25. 29. <ul><li>The ocean crust is forced under the continental crust. </li></ul><ul><li>As the rock from the ocean crust goes into the mantle, it melts and becomes magma. </li></ul>
  26. 30. mantle explosive volcanoes powerful earthquakes crust melts
  27. 31. Slip-sliding plates <ul><li>In some places in the world the plates are sliding past each other. </li></ul><ul><li>When plates slide past each other they often jam for several years. </li></ul><ul><li>This results in very powerful earthquakes. </li></ul>
  28. 32. Slip-sliding plates <ul><li>The San Andreas fault in California is such a fault. </li></ul><ul><li>This fault frequently causes large quakes. </li></ul><ul><li>In 1906 it destroyed the city of San Francisco. </li></ul>