ABSTRACT

In his 1994 essay ‘Evolutionary Perfection of a Small Molecule’, Nobel Laureate Konrad Bloch made the bold prediction that each intermediate step in the long biosynthetic pathway to cholesterol was once a fully adapted membrane molecule in ancient cells. He doubted, however that these primordial compounds would ever be found in the rock record.

Here I present the discovery of such molecules, protosteroids, in 1.6 to 0.8 billion-year-old sediments. These unexpected lipid fossils, long overlooked because of their unusual structures, confirm Bloch’s vision of stepwise molecular evolution.

The protosteroids reveal a previously hidden biosphere dominated by stem-group eukaryotes in Earth’s middle ages. Modern eukaryotes, the crown group that includes protists, algae, animals and plants, appear to have expanded only after ~800 million years ago, marking one of the most profound ecological turning points in Earth’s history that set the stage for complex life and the emergence of animals.

BIOGRAPHY

Jochen Brocks is a professor of palaeobiogeochemistry at the Research School of Earth Sciences, Australian National University. He is fascinated by arcane biological processes in Precambrian oceans, the early evolution of eukaryotes and the emergence of the first animals. To find clues about ancient life, he studies molecular fossils of biological lipids (biomarkers) that can be preserved in sedimentary rocks for billions of years.