Reconstructed setting· The columns of time

Carboniferous forest

359 Ma → 299 Ma

This backdrop shows a Carboniferous swamp forest: tall lycopsids with diamond-shaped leaf scars, tree ferns at their feet and a large insect in flight.

Backdrop representing a Carboniferous swamp forest: tall lycopsids with diamond-shaped leaf scars, tree ferns at their base, and a large insect in flight.

What the evidence shows

Arborescent lycopsids dominate the composition, their unbranched trunks carrying the diamond-shaped leaf scars by which they are identified in coal seams. Tree ferns and seed ferns accompany them, in a tropical wetland flora that also included medullosaleans and cordaitaleans. The large insect in flight relates the scene to the composition of the atmosphere: oxygen reached as much as 35 per cent in the Permo-Carboniferous, and since insects breathe by diffusion through a network of tracheae, the size they can attain depends on the oxygen content of the air.

Bounds and conventions

A wetland scene here represents an entire period, which also contained deserts and uplands. The oxygen value is a model output and not a measurement, and the models producing it differ from one another by several percentage points.