Oxygen reaches its all-time high
The atmosphere hits roughly 35% oxygen — the highest it has ever been.
- When
- Known to
- ± 10 million years
- Era
- Carboniferous, Paleozoic
Enormous burial of undecayed plant matter removes carbon from circulation and leaves the oxygen behind, pushing atmospheric concentrations to around 35%, against 21% today. Wildfires become frequent even in wet conditions, and charcoal is abundant in Carboniferous rocks. The elevated oxygen is the standard explanation for the period's giant arthropods, though the relationship is not as simple as it is often stated.