Earth & Atmospheric Science

8.18 Recall that the gases produced by volcanic activity formed the Earth’s early atmosphere
  • One theory suggests that during the first billion years of the Earth’s existence…
    • There was intense volcanic activity that released gases that formed the early atmosphere
      • At the start of this period, the atmosphere may have been like the atmospheres of Mars and Venus today, mainly CO2 with little or no O2(g)
      • Volcanoes also produced nitrogen which gradually built up in the atmosphere & there may have been small proportions of methane and NH3
8.19 Describe that the Earth’s early atmosphere was thought to contain…and interpret evidence relating to this
  • Little or no oxygen
  • A large amount of CO2
  • Water vapour
  • Small amounts of other gases
8.20 Explain how condensation of water vapour formed oceans
  • Water vapour condensed to form the oceans – H2O (g) -> H2O (l)
8.21 Explain how the amount of CO2 in the atmosphere was decreased when CO2 dissolved as the oceans formed
  • CO2 dissolved in the water and carbonates were precipitated producing sediments, reducing the amount of CO2 in the atmosphere
8.22 Explain how the growth of primitive plants used CO2 and released O2 by photosynthesis and consequently the amount of O2 in the atmosphere gradually increased
  • Algae & plants produced the O2 that is now in the atmosphere by photosynthesis

6CO2 + 6H2O -> C6H12O6 + 6O2

carbon dioxide + water –(light)-> glucose + oxygen

  • Algae first produced oxygen about 2.7 billion years ago and soon after this oxygen appeared in the atmosphere
  • Over the next billion years plants evolved and the % oxygen gradually increased to a level that enabled animals to evolve
  • Algae and plants decreased the % CO2 in the atmosphere by photosynthesis
8.23 Describe the chemical test for O2
  • Uses a glowing splint inserted into a test tube of the gas
    • Splint relights in oxygen
8.24 Describe how various gases in the atmosphere, including CO2, CH4 and water vapour, absorb heat radiated from the Earth, subsequently releasing energy which keeps the Earth warm: this is known as the greenhouse effect
  1. Electromagnetic radiation at most wavelengths from the sun passes through the Earth’s atmosphere
  2. The Earth absorbs some radiation and thus warms up (essential for life on Earth). But some heat is radiated from the Earth as infrared radiation.
  3. Some of this IR radiation is absorbed by greenhouse gases in the atmosphere
  4. Atmosphere warms up leading to the greenhouse effect and global warming 
8.25 Evaluate the evidence for human activity causing climate change, considering: the correlation between the change in atmospheric carbon dioxide concentration, the consumption of fossil fuels and temperature change, and the uncertainties caused by the location where these measurements are taken and historical accuracy
8.26 Describe: the potential effects on the climate of increased levels of CO2 and CH4 generated by human activity, including burning fossil fuels and livestock farming and that these effects may be mitigated: consider scale, risk and environmental implications
  • Increase levels of CO2 & CH4
  • Examples include
    • Driving (CO2)
    • Raising livestock (cows – CH4)
  • Based on peer-reviewed evidence, many scientists believe that human activities will cause the temperature of the Earth’s atmosphere to increase at the surface and that this will result in global climate change
    • But, it is difficult to model such complex systems as global climate change.
    • This leads to simplified models, speculation and opinions presented in the media that may be based on only parts of the evidence and which may be biased.

Biofuels

  • Biofuels, for example ethanol and biodiesel, are produced from plant material. There are economic, environmental and ethical issues surrounding their use.
  • Help decrease emissions of CO2 and therefore decrease impact of global warming