C9: specification

• Describe the composition of gases in the Earth's atmosphere using percentages

  • 80% nitrogen
  • 20% oxygen
• Describe how early intense volcanic activity may have helped form the early atmosphere and how

  the oceans formed

  • 1st billion of years...
  • early atmosphere was mostly carbon dioxide with no oxygen
  • volcanoes also released nitrogen, water vapour & methane
• Explain why the levels of carbon dioxide in the atmosphere changes as the oceans were formed

  • when water vapour condensed, it formed oceans
  • carbon dioxide removed as it dissolved into oceans
  • dissolved carbon formed sediments on seabed
  • algae absorbed some carbon dioxide to photosynthesise & marine animals formed with bones made of carbonates
• Explain why the levels of carbon dioxide in the atmosphere changes as the oceans were formed

  • when organisms die, they get buried by sediments; trapping carbon in them
• fossil fuels

  • crude oil & natural gas formed by plankton
  • coal made from thick plant deposits
  • limestone made of calcium carbonate deposits from skeletons
• State the approximate time in Earth's history when algae started producing oxygen and describe the

  effects of a gradually increasing oxygen level

  • algae evolved 2.7 billion years ago
  • oxygen level built up so more complex life forms could evolve
  • 200 million years ago, atmosphere reached what we have today: 80% nitrogen, 20% oxygen, under 1% of other gases
• Explain the ways that atmospheric carbon dioxide levels decreased

  1. photosynthesis of algae & green plants
  2. fossils trapping carbon
  3. oceans
• Name some greenhouse gases

  carbon dioxide, methane & water vapour
• describe how greenhouse gases cause an increase in earth's temperature

  • acts as an insulating layer
  • dont absorb short wavelengths from sun but absorbs long wavelengths reflected off of earth's surface & re-radiate it
• List some human activities that produce greenhouse gases

  1. deforestation: less tress so less CO2 is removed via photosynthesis
  2. burning fossil fuels: carbon 'locked up' by fossil fuels is released
  3. agriculture: more farm animals produce methane through digestion
  4. creating waste: more landfill sites so more CO2 released by decomposition of waste
• Evaluate arguments for and against the idea that human activities cause a rise in temperature that

  results in global climate change

  • temperature varies naturally but recently average has been increasing
  • most scientists agree that extra carbon dioxide from human activity is causing this which will lead to climate change
  • evidence for this has been peer reviewed so you know it's useful
  • lets of variable & hard to make model which isn't over simplified in regards to the earth's climate
  • led to speculation in media where stories can be biased
• State some potential side effects of global climate change, including discussing scale, risk and

  environmental implications

  • polar ice caps melt = rise in sea levels, increasing flooding
  • changes in rainfall patterns cause regions to get too much or little water
  • frequency & severity of storms will increase
  • changes in temperature may affect wild species, leading to differences in distribution
• Define the term carbon footprint

  carbon dioxide & greenhouse gases released over a life cycle of something