Earth's Atmosphere Evolution

Introduction

• Current Composition: ~80% Nitrogen, ~20% Oxygen, <1% other gases (CO2, water vapor, noble gases).
• Theory: Evolution of atmosphere over 4.6 billion years supported by evidence but still theoretical.

Early Earth's Atmosphere

• First Billion Years
  • Intense volcanic activity.
  • Emitted gases: Carbon dioxide (CO2), water vapor, nitrogen, methane, ammonia.
  • Atmosphere similar to Mars and Venus (CO2-rich).
• Formation of Oceans
  • Water vapor condensed into liquid, forming oceans.
  • CO2 dissolved in oceans, formed carbon precipitates, became seabed sediments.

Biological Influence

• Algae and Plant Evolution (~2.7 billion years ago)
  • Slow initial appearance of algae, followed by evolution of green plants.
  • Photosynthesis:
    • Process consuming CO2, releasing oxygen (O2).
    • Reduced atmospheric CO2, increased O2 over billions of years.
• Impact on Life: Increased oxygen supported evolution of complex life (animals).

Carbon Sequestration

• Carbon Storage
  • Dead algae and plants became buried in seabed sediments.
  • Over millions of years, these sediments compressed into sedimentary rocks, oil, and gas.
  • Substances Formed:
    • Crude Oil and Natural Gas: Primarily from plankton.
    • Coal: From thick deposits of dead plant material.
    • Limestone: From calcium carbonate in marine organism shells/skeletons.

Recap

• Volcanic Activity: Initial CO2-rich atmosphere.
• Ocean Formation: Absorbed CO2, forming sediments.
• Photosynthesis by Algae & Plants: Decreased CO2, increased O2.
• Sedimentary Rocks & Fossil Fuels: Created from dead organisms, sequestering carbon.
• Current Atmosphere: Dominated by nitrogen and oxygen due to evolutionary processes.

Conclusion

• Summary of atmospheric changes over geological time.
• Resulting in current atmospheric composition and fossil fuel reserves.
• Wrap-up: Key transformations and their impact on earth's atmosphere.