Reconstructed setting· The columns of time

Proterozoic world

2.5 Ga → 539 Ma

This backdrop shows the Proterozoic: a sea with oxygen but little of it, and algae attached to the floor that grow taller through the eon.

Backdrop representing an oxygenated but oxygen-poor sea, with algae attached to the floor whose height increases through the eon.

What the evidence shows

After the Great Oxidation the water contains oxygen, which the composition represents, but the concentration remains low across the 1,960 million years of the eon. Benthic macroalgae, that is, attached to the substrate, appear on the floor because algae are established ecological actors from the Proterozoic, and they are drawn taller in the later part of the band for a measured reason: the maximum size of macroalgae and the diversity of their forms both increase in the Neoproterozoic. The backdrop is therefore not identical from one end of the band to the other, which is rare on this timeline.

Bounds and conventions

A single composition represents two billion years, the longest interval any backdrop on this timeline has to cover. What it depicts is a plausible shallow marine setting and not a determined place: Proterozoic sea floors were highly varied, and the only constant the backdrop asserts is the low oxygen concentration.