Period· The columns of time

Statherian

1.8 Ga → 1.6 Ga

The period that gives the planet its long calm: continents stabilise, oxygen settles low, and the deep sea turns to sulfide for a billion years.

What the evidence shows

No glaciation, no mass extinction, an unusually steady carbon cycle: here begins the stretch known as the boring billion, under a name taken from the Greek for stable. The calm is not empty. With oxygen thin and sulfate washing off the newly stabilised continents, bacteria turn swaths of the deep ocean into water laced with hydrogen sulfide, which strips out the dissolved iron and the trace metals that nitrogen-fixing enzymes need. In Gabon, around 1.7 billion years ago, bodies of uranium ore sustain nuclear chain reactions on their own, which took two conditions at once: oxygen in the air to mobilise the uranium, and ore still rich enough in its fissile isotope, above three per cent. And in North China, 1.63 billion years ago, cells divide and fail to let go: unbranched filaments whose cells reach a fifth of a millimetre across, among the oldest multicellular eukaryotes known.

Bounds and conventions

Two conventional round numbers bound it, and they mark nothing. The boring billion they open is a description after the fact, with no agreed beginning or end, and its very dullness is now disputed: several authors read the same interval as a slow build-up rather than a pause. How far the sulfidic waters extended is estimated from proxies, not observed.

Sources

1. Cohen, K. M., Finney, S. C., Gibbard, P. L., Fan, J.-X. (2013). The ICS International Chronostratigraphic Chart. Episodes 36(3), 199–204, mise à jour continue, voir Cohen et al. (2025), Episodes.
2. Mukherjee et al. (2018), Scientific Reports · The Boring Billion, a slingshot for complex life on Earth
3. Canfield (1998), Nature · A new model for Proterozoic ocean chemistry
4. Gauthier-Lafaye (2002), Comptes Rendus Physique · 2 billion year old natural analogs for nuclear waste disposal: the natural nuclear fission reactors in Gabon
5. Miao et al. (2024), Science Advances · 1.63-billion-year-old multicellular eukaryotes from the Chuanlinggou Formation in North China