Period· The columns of time

Statherian

1.8 Ga → 1.6 Ga

The Statherian, from 1.8 to 1.6 billion years ago, opened a long stability: continents consolidated, oxygen settled low and the deep sea turned sulfidic for a billion years.

Period from which the long stability that follows proceeds: continents consolidate, oxygen settles at a low level, and the deep sea passes into a sulfidic regime for a billion years.

What the evidence shows

No glaciation, no mass extinction and a carbon cycle of unusual regularity characterise the period, whose name is formed on the Greek statheros, stable, and which opens the interval known as the boring billion. That stability is not an absence of events. Oxygen being scarce and sulfate washing off newly stabilised continents, sulfate-reducing bacteria turn portions of the deep ocean into water charged with hydrogen sulfide, which removes dissolved iron and also the metals required by nitrogen-fixing enzymes. At Oklo, in Gabon, around 1.7 billion years, bodies of uranium ore sustain chain reactions unaided, which two conditions made possible: atmospheric oxygen to mobilise the uranium, and ore still rich enough in the fissile isotope, above three per cent. In North China, at 1.63 billion years, unbranched filaments whose cells reach a fifth of a millimetre are among the oldest known multicellular eukaryotes.

Bounds and conventions

Two conventional round numbers bound the period without marking anything. The boring billion it opens is a description established after the fact, with no agreed beginning or end, and its dullness is now contested, several authors reading the same interval as a gradual establishment rather than a pause. The actual extent of the sulfidic waters is estimated from indirect proxies and not observed.