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  • Our changing planet
    • Structure of the Earth
      • The Earth is made of layers called the core mantel and crust with the atmosphere around the outside
      • The Earth`s limited resources come from its crust, the ocenas and the atmosphere
    • The restless Earth
      • The Earth`s crust and upper mantle is cracked into tectoic plates which are constantly moving
      • The tectonic plates move because of convection currents in the mantle that are caused by radioactive decay
      • Earthquakes and volcanoes happen where tectonic plates meet, but it is difficult to predict accurately when and where the earthquakes will happen
      • Wegener`s theory of continental drift was not accepted for many years
    • The Earth`s atmosphere in the past
      • The Earth`s early atmosphere was formed by volcanic activity
      • It probably consisted mainly of carbon dioxide. There may also have been water vapour together with traces of methane and ammonia
      • As plants spread over the Earth, levels of oxygen in the atmosphere increased
    • Life on Earth
      • There are many theories about how life began on Earth
      • One theory states that the compounds needed came from reactions involvng hydrocrabons and ammonia and lighting providing energy
      • All the theories about how life started on Earth are unproven and so we cannot be sure how life began
    • Gases in the atmosphere
      • Most of the carbon dioxide in the early atmosphere became locked up in sedimentary rocks
      • About four-fifths(almost 80%) of the atmosphere is nitrogen and about one-fifth(just over 20%) is oxygen
      • The main gases in the air can be seperated by fractional distillation. These gases are used in industry as raw materials
    • Carbon dioxide in the atmosphere
      • Carbon moves into and out due to plants, animals, the oceans and the rocks
      • The amount of carbon dioxide in the Earth`s atmosphere has risen in the recent past largely due to the amount of fossil fuels we now burn


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