Lecture Notes: Origins of Life on Earth

Introduction

• Uncertainty about how life originated on Earth.
• Discussion of the limits of scientific understanding.
• Historical parallels: Early microbiologists and the discovery of microorganisms causing diseases.

Evidence of Early Life

• Fossils of Bacteria: Fossils dating back 3.5 billion years.
• Stromatolites: Layers of bacteria that trap sediment, forming rocks over millions of years.
  • Modern cyanobacteria form similar structures today.
  • Fossilized stromatolites can be carbon-dated.
• Cyanobacteria Fossils: Found in Western Australia, showing structures similar to modern-day cyanobacteria.

Impact of Early Life on Earth

• Early life forms altered Earth's chemistry.
• Anaerobic Bacteria: Dominant life forms that didn't use oxygen.
• Introduction of Oxygen:
  • Oxygen-producing organisms emerged after about a billion years.
  • Oxygen initially absorbed by Earth's minerals (e.g., iron oxidation).
  • Great Oxygen Catastrophe:
    • Oxygen became abundant in the atmosphere.
    • Oxygen was toxic to many early anaerobic organisms, leading to mass extinction.
    • Some organisms adapted to use oxygen, leading to evolution of modern life forms.

Conclusion

• Overview of early life forms and the evidence supporting their presence on Earth 3.5 billion years ago.
• Brief mention of upcoming topics: Theories on how life changes over time.