C11 - Earth's Atmosphere

• The Earth's atmosphere is dynamic and forever changing
• The causes of these changes are sometimes man-made and sometimes part of many natural cycles
• Scientists use very complex software to predict weather and climate change as there are many variables that can influence this
• The problems caused by increased levels of air pollutants require scientists and engineers to develop solutions that help to reduce the impact of human activity
• Proportions of different gases in the atmosphere for 200 million years


  • About four-fifths (approximately 80%) nitrogen
  • About one-fifth (approximately 20%) oxygen
  • Small proportions of various other gases, including carbon dioxide, water vapour and noble gases
• Theories about what was in the Earth's early atmosphere and how the atmosphere was formed have changed and developed over time
• Evidence for the early atmosphere is limited because of the time scale of 4.6 billion years
• Formation of the early atmosphere


  1. Intense volcanic activity released gases that formed the early atmosphere

  2. Water vapour condensed to form the oceans

  3. At the start, the Earth's atmosphere may have been like the atmospheres of Mars and Venus today, consisting of mainly carbon dioxide with little or no oxygen gas

  4. Volcanoes produced nitrogen which gradually built up in the atmosphere

  5. There may have been small proportions of methane and ammonia
• Reduction of carbon dioxide in the atmosphere


  1. Carbon dioxide dissolved in the water and carbonates were precipitated producing sediments

  2. Algae and plants produced the oxygen that is now in the atmosphere by photosynthesis

  3. Algae first produced oxygen about 2.7 billion years ago

  4. Over the next billion years plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve

  5. Algae and plants decreased the percentage of carbon dioxide in the atmosphere by photosynthesis

  6. Carbon dioxide was also decreased by the formation of sedimentary rocks and fossil fuels that contain carbon
• Greenhouse gases


  • Water vapour, carbon dioxide and methane are greenhouse gases
  • Greenhouse gases in the atmosphere maintain temperatures on Earth high enough to support life
• Greenhouse effect


  Interaction of short and long wavelength radiation with matter
• Some human activities increase the amounts of greenhouse gases in the atmosphere
• Human activities that increase greenhouse gases

  • Carbon dioxide
  • Methane
• 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
• 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
• Evaluating evidence on global climate change


  • Evaluate the quality of evidence in a report
  • Describe uncertainties in the evidence base
  • Recognise the importance of peer review of results and of communicating results to a wide range of audiences
• An increase in average global temperature is a major cause of climate change
• Potential effects of global climate change


  • Describe briefly four potential effects
  • Discuss the scale, risk and environmental implications
• Carbon footprint


  The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event
• Reducing carbon footprint


  Reducing emissions of carbon dioxide and methane
• Actions to reduce emissions may be limited
• The combustion of fuels is a major source of atmospheric pollutants
• Gases released into the atmosphere when a fuel is burned


  • Carbon dioxide
  • Water vapour
  • Carbon monoxide
  • Sulfur dioxide
  • Oxides of nitrogen
• Solid particles and unburned hydrocarbons may also be released that form particulates in the atmosphere
• Carbon monoxide


  A toxic gas that is colourless and odourless and so is not easily detected
• Effects of sulfur dioxide and oxides of nitrogen


  • Cause respiratory problems in humans
  • Cause acid rain
• Effects of particulates


  • Cause global dimming
  • Cause health problems for humans