C13

• 4.6 billion - 2.7 billion years ago:

  • CO2 released by volcanoes was biggest component in atmosphere
  • very little O2
  • some N2 released by volcanoes
  • H2O released by volcanoes but existed as vapour bc. Earth was too hot for it to condense
  • ammonia (NH3), methane (CH4) may have been present
• 2.7 billion to 200 million years ago:

  • CO2 begins to reduce bc. water condenses to form oceans in which it dissolves and algae (and later plants) start to PS
  • CO2 precipitates in oceans as solid carbonates (sediments) that form rocks
  • CO2 taken in by plants and animals and when they die, CO2 is locked up as fossil fuels
  • O2 starts to increase bc. of PS
  • N2 is stable molecule so slowly builds up over time
  • H2O vapour starts to decrease as Earth cools and oceans are formed
• 200 millions years ago to present day:

  • about 0.04% of CO2
  • about 21% of O2
  • about 78% of N2
  • about 0.9% of argon (Ar)
  • very little H2O vapour - forms clouds as part of water cycle
  • small amounts of noble gases
• Greenhouse gases:

  • CO2, methane, water vapour
  • absorb radiation and maintain Earth’s temp to support life
  • in last 150 years, inc. in CO2 bc. combustion of fossil fuels and deforestation; inc. in methane bc. planting rice fields, cattle farming
• Scientists say inc. in greenhouse gases means inc. in Earth’s temp, leading to global warming. This leads to global climate change - how overall weather patterns over many years and across planet will change. Effects of this include:

  • sea levels rising
  • extreme weather events
  • polar ice caps melting
  • changes to ecosystems and habitats
  • changes in amount and time of rainfall
• total CO2, methane and other greenhouse gases released into atmosphere by person, product or process is called carbon footprint
• carbon monoxide - incomplete combustion of fuels - colourless and odourless toxic gas
• particulates (soot and unburnt hydrocarbons) - incomplete combustion of fuels especially in diesel engines - causes global dimming, respiratory problems and potential cause to cancer
• sulfur dioxide - sulfur impurities in fuel reacting with O2 from air - causes acid rain and respiratory problems
• oxides of nitrogen - N2 from air being heated near an engine and reacting with O2 - causes acid rain and respiratory problems