This is the Proterozoic Eon, the middle phase of Earth’s history between the ancient Archean Eon and the Phanerozoic Eon (the Phanerozoic is the eon that contains all the familiar periods — Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene, Quaternary — that is to say, the last 540 million years of Earth’s 4.5-billion-year history).

At the time the Roraima sediments were being deposited, photosynthetic life had existed for more than a billion years — it is photosynthesis that had produced the first significant accumulation of oxygen in Earth’s atmosphere, transforming the atmospheric chemistry of the planet in what geologists call the Great Oxidation Event.

But multicellular life — the kind of life that leaves recognizable fossils — had barely begun its history.

The organisms of the time were primarily microbial: bacteria, archaea, algae, possibly the earliest simple multicellular forms.