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Structure Of The Earth
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Structure Of The Earth


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for teachers of science

for teachers of science

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