History of Life on Earth

• Geological timescale divided into 4 eons: Hadean, Archaean, Proterozoic, Phanerozoic
• Environmental changes cause mass extinctions
• Archaean eon:

  • Prokaryotic cells, anaerobic organisms
  • Uncertain if heterotrophs or autotrophs came first
  • Rise of cyanobacteria led to oxygen increase in atmosphere
  • Mitochondria and chloroplasts likely derived from endosymbiosis
• Proterozoic eon:

  • Multicellular life
  • First animals (invertebrates)
• Phanerozoic eon:

  • Paleozoic era saw invertebrate diversification, land colonization
  • Mesozoic era: Rise and fall of dinosaurs
  • Cenozoic era: Mammals and flowering plants diversify, hominins evolve
• Quaternary period:

  • Ice ages
  • Homo sapiens appear about 200,000 years ago