EARTH × LIFE × ATMOSPHERE

The Great Oxidation Event

~2.4 billion years ago

Proterozoic · Paleoproterozoic · Siderian

For hundreds of millions of years, microbes had been making oxygen, and the world had been swallowing it as fast as they made it. Then, around 2.4 billion years ago, the world could swallow no more, and the oxygen stayed. The moment is written in sulfur: a telltale isotope pattern that can only form in air without oxygen or ozone disappears from the rock record, everywhere on Earth, and never returns. The whole transition took some two hundred million years, the level rising and crashing before it finally held; the planet has kept an oxygenated sky ever since.

Why it matters

Life never inflicted a larger reversal on its own planet, and the planet never went back. Oxygen poisoned most of what was then alive, wrecked the methane greenhouse and let the world freeze over; and at the same stroke it made respiration possible, the slow burn that draws energy from food using oxygen. Everything that has breathed since, ourselves included, lives in the world this event made.

Dating & uncertainty

The start is bracketed between 2.46 and 2.33 billion years ago. Whether oxygen then stayed up, or fell back and became permanent only around 2.22 billion, changes what the first ice ages were responding to, and it is still argued from sulfur records that contradict each other.

Sources

1. Gumsley et al. (2017), PNAS · Timing and tempo of the Great Oxidation Event
2. Luo et al. (2016), Science Advances · Rapid oxygenation of Earth's atmosphere 2.33 billion years ago
3. Poulton et al. (2021), Nature · A 200-million-year delay in permanent atmospheric oxygenation
4. Uveges et al. (2023), Nature Communications · Reconciling discrepant minor sulfur isotope records of the Great Oxidation Event

Earth history as one day

11:18:4512 h 41 min before midnight

if Earth’s 4.54 billion years were compressed into a single day