From poison to breath: how cyanobacteria seeded Earth’s oxygen-rich world
Oxygen, now essential to life, started as a poisonous byproduct released by cyanobacteria about 2.4–2.5 billion years ago, triggering the Great Oxidation Event that poisoned much of the anaerobic biosphere and reshaped Earth’s chemistry. As some microbes adapted to oxygen, they evolved enzymes and aerobic respiration, enabling far more energy production and the rise of larger, more complex life. The modern atmosphere remains a steady-state maintained by ongoing photosynthesis, with cyanobacteria still producing oxygen today.