Reconstructed setting· The columns of time
Proterozoic world
2.5 Ga → 539 Ma
An oxygenated sea that is still poor in oxygen, with seaweeds on the floor, growing taller as the eon goes on.
What the evidence shows
After the Great Oxidation Event the water holds oxygen, and the scene is drawn accordingly, but the quantity stays low for all 1,960 million years of the eon. Benthic macroalgae are drawn on the sea floor because seaweeds have been ecological players since the Proterozoic, and they stand taller in the younger part of the band for a reason that is measured rather than assumed: the maximum size and the shape diversity of macroalgae both increase through the Neoproterozoic. The backdrop therefore changes within itself, which few others on this timeline do.
Bounds and conventions
A single scene for two billion years, the longest stretch any backdrop on this timeline has to cover. What it shows is a plausible shallow marine setting, not a place: the Proterozoic sea floor varied enormously, and the only constant the backdrop asserts is the low oxygen.