An atmosphere with no oxygen
Air of nitrogen, carbon dioxide and methane — lethal to almost everything alive today.
- When
- Known to
- ± 100 million years
- Era
- Eoarchean, Archean
Free oxygen is essentially absent; what little is produced is consumed immediately by dissolved iron and volcanic gases. Methane from early microbes may have built an organic haze, tinting the sky orange and shielding the surface from ultraviolet light. This composition persists for well over a billion years, and the iron-rich oceans it permits are what make banded iron formations possible.