Reconstructed setting· The columns of time

Archean world

4.03 Ga → 2.5 Ga

This backdrop shows the Archean: shallow seas worked by swell, with low microbial mounds on the floor, the first composition on the timeline with a horizon and living things.

Backdrop representing shallow seas worked by swell, with low microbial mounds on the floor. It is the first composition on the timeline to include a horizon and living organisms.

What the evidence shows

The wave-worked shallows proceed from the microbial mat facies of Strelley Pool, which preserves crescent ripples shaped by wind, evidence of a beach and therefore of shallow water. The mounds appear only from 3.7 billion years, the age of the oldest reported stromatolites, at Isua in Greenland, and their broad, low form is deliberate: tall columnar stromatolites appear only in the Proterozoic, and depicting them here would import a later state into an earlier scene.

Bounds and conventions

The date at which the mounds appear is contested: the Isua structures have been interpreted as microbial and as tectonic, and at this degree of metamorphism the two are difficult to separate. The backdrop depicts them from 3.7 billion years, which corresponds to the publication and not to a settled result.