Chemistry - C1.7 - Our Changing Planet

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C1.7.1 - Structure of the Earth

  • Earth is almost spherical, diameter of ~12800kn
  • Crust: at the surface, varies in thickness - between 5km and 70km
  • Mantle: under crust, ~3000km thick, goes nearly halfway to the centre, almost entirely solid but parts can flow very slowly
  • Core: centre, ~half diameter of Earth, high proportion of iron and nickel, liquid outer and solid inner parts
  • Atmosphere: surrounds Earth, most air is within 10km of the surface, most of the atmosphere is within 100km of the surface
  • All raw materials we use come from the crust, oceans and atmosphere - resources avaliable to us are limited
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C1.7.2 - The Restless Earth

  • Earth's crust and upper mantle is cracked into pieces - tectonic plates
  • Tectonic plates - move a few centimeters a year due to convection currents in the mantle beneath caused by energy released by decay of radioactive elements heating the mantle
  • Huge forces where plates meet -> rocks give way - changing shape or moving suddenly -> earthquakes, volcanoes or mountains form - still unsure about what is happening in the Earth so can't predict when earthquakes or volcanic erruptions will happen
  • Alfred Wegener - put forward idea of continental drift in 1915 - ideas weren't accepted as he couldn't explain why continents moved - believed Earth was shrinking as it cooled but in 1960s new evidence was found and the theory of tectonic plates was developed
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C1.7.3 - The Earth's Atmosphere In the Past

  • Earth formed about 4.5 billion years ago - 1st billion years - surface was covered with volcanoes that released CO2, water vapour and nitrogen
  • Cooled - water vapour became oceans - early atmosphere mainly CO2 and some water vapour, some believe there was nitrogen, methane and ammonia
  • Next 2 billion years - bacteria, algae and plants evolved - algae and plants used CO2 for photosynthesis -> released O2 - as no of plants increased, % of CO2 in atmosphere decreased and % of O2 increased
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C1.7.4 - Life on Earth

  • Plants that produced O2 evolved from simple organisms (eg. plankton and algae) - don't know how molecules of the simplest living things were formed - scientists suggest theories but can't be sure - insufficient evidence
  • Miller-Ulrey experiment - 1952, two scientists did experiment on what they thought was in the early atmosphere (mixture of H2O, NH3, CH4) and high voltage spark (lightening) - after a week amno acids (building blocks of protein) were produced
  • Other theories - since 1950s theories about what was in the atmosphere has changed, but amino acids have been produced using different gases - on theory suggest organic molecules formed a 'primordial soup' and amino acids in mixture mixed to make proteins - other theories are suggested, but there is no evidence to prove any
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C1.7.5 - Gases In the Atmosphere

  • Plants took up CO2 in early atmosphere -> animals ate plants -> carbon ended up in remains as sedimentary rocks and fossil fuels, limestone formed from marine animals shells and skeletons, fossil fuels contain carbon and hydrogen from plants and animals
  • Carbon dissolves in oceans or forms insoluable compounds, deposited on seabed -> sedimentary rocks
  • 200 million years ago - gas % similar to today - 78% N, 21% O, 0.9% Ar, 0.04% CO2, trace amounts of other gases (eg. water vapour, noble gases)
  • Gases in air have different boiling points -> fractional distillation
  • Fractional distillation of liquid air done by industrybto produce pure O or liquid N - important uses - air is cooled to -200C and fed in column - nitrogen separated and further distillation needed to separate oxygen and argon
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C1.7.6 - Carbon Dioxide In the Atmosphere

  • CO2 % remained the same for last ~200 million years - natural processes that move carbon in and out of the atmosphere are balanced
  • Processes involve carbon compounds in plants, animals, the oceans and rocks - the organic carbon cycle shows these processes
  • CO2 dissolves in water (particularly oceans) - reactions of inorganic carbonate compounds are also imortant in maintaining balance
  • Human activity has increased amount of CO2 released dramatically - particularly burning fossil fuels
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