Formation of Earth's Atmosphere

Early Earth Conditions

• Age of Earth: 4.54 billion years.
• Inhospitable Environment:
  • Significant volcanic activity.
  • Early atmosphere composed mainly of carbon dioxide (CO2) and water vapor (H2O).

Development of Oceans

• Cooling of Earth:
  • Water vapor condensed to form oceans.
  • Atmosphere mainly comprised of CO2, with trace amounts of ammonia (NH3) and methane (CH4).

Introduction of Algae and Plants

• Importance:
  • Algae and plants were pivotal in changing the atmosphere.
  • They performed photosynthesis:
    • Photosynthesis Equation: CO2 + H2O → Glucose + O2 (oxygen).

Formation of Metal Oxides

• Oxygen Production:
  • Initial oxygen reacted with metals to form metal oxides.
  • Evidence of metal oxides can be seen in rock formations as red bands.
• Excess Oxygen:
  • Once metals were oxidized, free oxygen began accumulating in the atmosphere.

Present-Day Atmosphere

• Gas Composition:
  • Nitrogen (N2): 78%
  • Oxygen (O2): 21%
  • Carbon Dioxide (CO2): 0.04%
  • Argon (Ar): 0.9% (less commonly examined).
• Examination Tip:
  • Be able to label a pie chart with the percentages of N2, O2, and CO2.

Learning Outcomes

• Explain the formation of the original atmosphere.
• Understand the development of the oxygen-rich atmosphere.
• Recall the percentages of gases in the current atmosphere.