LIFE × EVOLUTION

A Lost World, Read in Its Molecules

~1.64 billion to 800 million years ago

Proterozoic · Paleoproterozoic · Statherian

For eight hundred million years the seas were full of organisms nobody knew existed, and a molecule gave them away. The sterol that stiffens the membrane of every complex cell is assembled in stages; mid-Proterozoic rocks are loaded with the half-built versions from the middle of that line, and chemists had walked past them for decades while looking for the finished product. Making any of them takes oxygen, so their owners lived in water that already had some. Deep-branching eukaryotes or bacteria, they held the ocean from about 1.64 billion years ago until roughly 800 million, when modern eukaryotes and red algae took it over.

Why it matters

Two clocks disagreed: genes placed the common ancestor of all complex cells deep in the Proterozoic, while the rocks showed almost nothing for the billion years that follow. The gap was never in life. It was in what we knew how to look for.

Dating & uncertainty

These molecules were overlooked for decades because chemists were looking for modern sterols. They are intermediates of the same pathway, predicted in the 1960s and only recognised in rocks in 2023. Whether their makers were stem eukaryotes, bacteria, or both is not settled.

Sources

1. Brocks et al. (2023), Nature · Lost world of complex life and the late rise of the eukaryotic crown
2. Gold et al. (2017), Nature · Paleoproterozoic sterol biosynthesis and the rise of oxygen
3. Brocks et al. (2017), Nature · The rise of algae in Cryogenian oceans and the emergence of animals

Earth history as one day

15:19:498 h 40 min before midnight

if Earth’s 4.54 billion years were compressed into a single day