earth and atmospheric science

• the gases produced by volcanic activity formed the Earth’s early atmosphere
• Earth’s early atmosphere was thought to contain:

  • little or no oxygen
  • a large amount of carbon dioxide
  • water vapour
  • small amounts of other gases

  evidence of this is mars and venus, which have atmospheres mainly composed of carbon-dioxide, thought to have been released by volcanoes
• formation of oceans:

  • the earth cooled down, causing water vapour in the atmosphere to condense into large amounts of water
• amount of carbon-dioxide decreased in the atmosphere when oceans were formed because:

  • carbon dioxide is a very soluble gas
  • as the oceans formed, carbon dioxide dissolved in the water and the amount in the atmosphere decreased
• photosynthesis by primitive plants and algae caused the removal of carbon dioxide from the air and the release of oxygen. This had two effects:

  • the amount of carbon dioxide decreased further
  • the amount of oxygen in the atmosphere gradually increased
• chemical test for oxygen:

  • insert​ ​a​ ​glowing​ ​splint​ ​​into​ ​a​ ​test​ ​tube​ ​of​ ​a gas
  • splint​ ​relights​ ​if oxygen is present