The atmosphere

• Describe the properties of gases in the modern atmosphere

  • around 80% of N2
  • 20% of O2
  • small quantities of CO2, H2O and noble gases
• describe Earth’s early atmosphere and how it was formed

  1. earth was hot when it was formed
  2. there was significant volcanic activity
  3. gases have been released from these volcanoes
  4. these gases included CO2, N2, CH4, NH3, H2O
• how did the amount of oxygen in the atmosphere increase?

  • algae and plants produced the atmospheric O2 by photosynthesis which can be represented by the equation:6CO2 + 6H2O > C6H12O6 + 6O2
  • as the amount of O2 gradually increased, there were more plants that produced more oxygen
• how did the amount of carbon dioxide in the atmosphere decrease?

  1. some was dissolved in the oceans, where it reacted with metal ions to form insoluble carbonates such as CaCo2 or was taken in by animals to become a part of skeleton. When an animal dies, it becomes a sedimentary rock
  2. some CO2 was used in photosynthesis to make oxygen