Evolution of Earth’s Atmosphere

• 1. Volcanic activity releases CO2, CH4, H2O and NH3. - The surface of the Earth cooled to the point where the water vapour could condense (temperature below 100°C) into liquid water, (resulting in rain as suspended water particles dropped) forming oceans.
• 2. CO2 dissolved into newly formed oceans and photosynthesising plants (algae and green plants) evolved in the oceans, removing CO2 and releasing oxygen.
• 3. Ammonia and methane reacted with the oxygen to form nitrogen gas and water (nitrogen built up overtime in atmosphere) - nitrogen also produced due to denitrifying bacteria (nitrates from decaying plants).
• 4. Carbon from CO2 is locked in sedimentary rocks as carbonates and fossil fuels - marine animals with shells evolved and used CO2 to form their shells, when animal dies, shell sinks to bottom of ocean forming carbonate rocks like chalk and limestone - prevented carbon being released.
• Large number of marine animals and trees died and were buried under layers of rock and mud - over time these organisms decayed forming fossil fuels like crude oil and coal which locked up carbon.
• 5. Some of the oxygen is converted into ozone - a layer which blocks out harmful ultraviolet rays which allows for the development of new life on land.
• Modern atmosphere approximate composition:

  • 78% nitrogen
  • 21% oxygen
  • 0.04% carbon dioxide
  • 0.9% argon
  • Water vapour varies
  • 0.1% other gases (noble gases)
• Production of gases in atmosphere:

  • Water (6H2O) + Carbon dioxide (6CO2) -> glucose (C6H12O6) + oxygen (6O2)
  • Ammonia (4NH3) + oxygen (3O2) -> water (6H2O) + nitrogen (2N2)
• • Gases in air can be separated using fractional distillation - these gases can be separated from each other as they have different boiling points.
• Nitrogen

  • Used as a cryogenic (very cold) liquid and providing unreactive atmospheres for food packing (slow down food spoilage) and certain reaction (prevent reactions with oxygen).
• Oxygen

  • Used in medical treatment for respiratory issues and various industrial processes, like removal of carbon impurities from steel.
• Argon

  • Used to provide an interactive atmosphere for certain chemical reactions (extraction of titanium using sodium) and in certain industrial processes (arc welding - lightbulbs, glow tubes.
• Neon

  • Used as a cryogenic (very cold) liquid and for production of certain lasers and neon signs.
• Radon

  • Cancer treatment, tumor treatment.
• Helium

  • Balloons, artificial atmosphere (lighter than air).
• Carbon dioxide

  • Fire extinguisher, fizzy drinks.