Reconstructed setting· The columns of time
Carboniferous forest
359 Ma → 299 Ma
Tall scale-trees with diamond-patterned trunks, tree ferns beneath them, and an insect on the wing that could not fly today. The air held more oxygen than it ever has since.
What the evidence shows
Arborescent lycopsids dominate, and their unbranched trunks carry the diamond leaf-scar pattern that makes them recognisable in coal seams. Tree ferns and seed ferns stand alongside them, in a tropical wetland flora that also held medullosans and cordaitaleans. The giant flying insect is what ties the scene to the atmosphere: oxygen reached as much as 35 per cent in the Permo-Carboniferous, and insects breathe by diffusion through tubes, so the size an insect can reach depends on how much oxygen the air holds.
Bounds and conventions
A wetland scene standing for a period that also had deserts and uplands. The oxygen figure is a model output rather than a measurement, and the models that produce it disagree by several percentage points.