Oxygenic photosynthesis evolves
Something learns to split water with sunlight — the single most consequential innovation in Earth's history.
- When
- Known to
- ± 200 million years
- Era
- Mesoarchean, Archean
Cyanobacteria develop a photosystem able to break the oxygen-hydrogen bond in water, a far harder chemistry than the sulfide-splitting that came before. Water is effectively unlimited, so the biosphere's energy ceiling lifts enormously — and the waste product is free oxygen. Genetic clocks place the last common ancestor of living cyanobacteria near 2.9 billion years ago, with the capability itself likely established by 3.0. Every breath taken since depends on this.