garden/the-great-oxygenation.md

The Great Oxygenation

• The diverity of [bacteria] exploded during the [Archaean], leading to the evolution of [Cyanobacteria]
  • This does not mean that Spirulina existed during the [Archaean]: it is a modern organism
• There was almost no O₂ in the atmosphere before the [Archaean]-[Proterozoic] break
  • No O₂ means no formation of peroxides
  • Peroxides are dangerous to many cells as they rob electrons from proteins, fatally altering them
• Cells had to develop anti-oxidation defenses, including catalase
• Cells had two ways to adapt to O₂
  1. Become a strict anaerobe, and avoid oxygen-containing habitats
  2. Tolerate O₂
     • O₂ toleration can easily lead to aerobic metabolism