C13 - The Earth's Atmosphere

• Earth's atmosphere: 78% nitrogen, 21% oxygen, 0.04% argon
• Early atmosphere made of mainly carbon dioxide and water vapour, with small amounts of methane, ammonia and nitrogen released from volcanoes. As Earth cooled water vapour condensed and formed the oceans. Carbon dioxide dissolved into oceans and forming carbonates and being precipitated out (made solid). Photosynthetic organisms evolved decreasing amount of CO2 in atmosphere and increasing O2 levels in atmosphere. Once enough oxygen was in the atmosphere, it could support animals, which carry out respiration releasing CO2.
• Combustion of fossil fuels has increased the amount of CO2 in atmosphere as well as other harmful gases such as nitrogen oxides and sulfur dioxide. Carbon particles and carbon monoxide can also be released as a result of incomplete combustion.
• The Greenhouse Effect:

  1. Greenhouse layer includes gases like CO2, methane and water vapour, maintain the temperature on Earth high enough to support life.
  2. Greenhouse layer allows short wavelength radiation from Sun to pass
  3. Earth absorbs some radiation to warm up and the rest is re-radiated out into the atmosphere
  4. Some radiation absorbed by greenhouse layer and lower atmosphere warms up
  5. Some radiation goes into space
• Amount of greenhouse gases increased by: Combustion of fossil fuels, deforestation, agriculture.