Early Atmosphere

• Why are there many theories of the early atmosphere?

  • Little evidence
  • Time scale of 4.6 billion years
• Main theory of Evolution Early Atmosphere

  1. During the first billion years of Earth's existence, there was intense volcanic activity / eruptions.
  2. This released gases that formed the early atmosphere.
• How were oceans formed?

  1. Water vapour in the atmosphere cooled and condensed to form oceans.
  2. The temperature fell below 100 degrees.
• Gases present in the Early Atmosphere :

  1. Water Vapour
  2. Nitrogen
  3. Methane
  4. Ammonia
• Early Earth's similarity with Venus and Mars today :

  1. Consisting of mainly carbon dioxide gas
  2. Little or no oxygen gas
• How Volcanoes gradually produced Nitrogen, Methane and Ammonia?

  • intense volcanic eruptions
  • including small proportions of methane and ammonia
• Other ways Nitrogen had formed?

  1. Ammonia in the Earth's early atmosphere reacted with oxygen
• Dissolution of carbon dioxide in the oceans : Decreasing carbon dioxide


  • Carbon dioxide dissolved in oceans
  • Carbon dioxide precipitate forming sediments
  • This reduced the amount of carbon dioxide in the atmosphere
• Describe and explain how the surface of the early Earth and its atmosphere have changed to form the surface of the Earth and its atmosphere today (6)

  1. Oxygen increased = plants / algae developed using carbon dioxide for photosynthesis, producing oxygen. Thus, carbon dioxide decreased.
  2. Water vapour in the atmosphere cooled and condensed to form oceans.
  3. Carbon dioxide decreased because carbon dioxide dissolved in oceans. Carbon dioxide became locked up in sedimentary rocks.
  4. Nitrogen formed because ammonia from early atmosphere reacted with oxygen
• Explain how carbon dioxide is released from limestone.

  1. Calcium carbonate
  2. Thermal decomposition
• How oxygen increased?

  1. Algae and plants produced oxygen NOW in the atmosphere by photosynthesis.
• Word equation for photosynthesis

  Carbon dioxide + water --> glucose + oxygen
• Symbol equation for photosynthesis (balanced)

  6CO2 + 6H20 --> C6H12O6 + 6O2
• First presence of Algae

  1. First produced oxygen about 2.7 billion years ago.
• Oxygen presence 


  1. Soon after algae, oxygen appeared in the atmosphere
• Plant evolution

  1. Over the next billion years, plants evolved and the percentage of oxygen gradually increased.
  2. Increased to a level that enabled animals to evolve.
• 2 ways carbon dioxide has decreased

  1. Plants and algae developed using carbon dioxide for photosynthesis, decreasing the level of carbon dioxide in the atmosphere.
  2. Dissolved into oceans. Carbon dioxide become locked up in sedimentary rocks.
• Fossil fuels and carbon dioxide

  1. Carbon dioxide decreased because it dissolved into oceans. Carbon dioxide became locked up in fossil fuels.
• One reason why nitrogen has increased overtime

  1. Very unreactive
• Coal, Crude Oil, Natural Gas

  • Fossil fuels
• The percentage of argon in the Earth’s atmosphere today is the same as it was in the Earth’s early atmosphere. Suggest why.

  • Argons gas is unreactive / inert
  • A noble gas = Group 0