Scientists discover the ‘Lost World’ of our early ancestors in rocks billions of years old

A multinational research team has discovered ancient protosteroids in rocks, indicating that complex life existed 1.6 billion years ago. These molecules offer new insights into the evolution of complex life and reconcile discrepancies between the traditional and lipid fossil records.

Newly discovered records of so-called protosteroids turned out to be surprisingly abundant during Earth’s Middle Ages. The primordial molecules were produced at an earlier stage of eukaryotic complexity—extending the current record of fossil steroids from 800 and up to 1,600 million years ago. Eukaryotes is the term for a kingdom of life including all animals, plants, and algae and separated from bacteria by a complex cell structure that includes a nucleus as well as more complex molecular machinery.

“The highlight of this discovery is not simply an extension of the current molecular record of eukaryotes,” says Christian Holmann, one of the participating scientists from the German Research Center for Geosciences (GFZ) in Potsdam. “Given that the last common ancestor of all modern eukaryotes, including us humans, was probably able to produce ‘common’ modern sterols, the chances are high that the eukaryotes responsible for these rare signatures belong to the stem of the phylogenetic tree.’

This “stem” represents the common ancestral lineage that was the ancestor of all still-living branches of eukaryotes. Its representatives are long gone, but details of their nature may shed more light on the conditions surrounding the evolution of complex life. Although more research is needed to estimate what percentage of protosteroids may have had a rare bacterial source, the discovery of these new molecules not only reconciles the geological record of traditional fossils with that of fossil lipid molecules, but provides a rare and unprecedented look at a lost world of ancient life. The competitive death of stem-group eukaryotes, marked by the first appearance of modern fossil steroids about 800 million years ago, may reflect one of the most abrupt events in the evolution of increasingly complex life.

“Almost all eukaryotes biosynthesize steroids, such as cholesterol, which is produced by humans and most other animals,” adds Benjamin Nettersheim of MARUM, University of Bremen, who co-first authored the study with Jochen Brox of Australian National University (ANU) – “because of the potentially adverse health effects of elevated cholesterol levels in humans, cholesterol does not have the best medical reputation. However, these lipid molecules are an integral part of eukaryotic cell membranes, where they support various physiological functions. By looking for fossilized steroids in ancient rocks, we can trace the evolution of increasingly complex life.

Nobel Laureate Konrad Block already speculated about such a biomarker in an essay almost 30 years ago. Bloch suggests that the short-lived intermediates in modern steroid biosynthesis were not always intermediates. He believed that lipid biosynthesis evolved in parallel with changing environmental conditions throughout Earth’s history. Unlike Block, who did not believe that these ancient intermediates could be found, Nettersheim began looking for protosteroids in ancient rocks that had been deposited at a time when these intermediates could actually be the final product.

But how do we find such molecules in ancient rocks? “We used a combination of techniques to first convert various modern steroids into their fossil equivalent; otherwise we wouldn’t even know what to look for,” says Jochen Brocks. Scientists have ignored these molecules for decades because they don’t fit typical molecular search images. “Once we figured out our target, we found that dozens of other rocks, taken from billions of years of waterways around the world, flowed with similar fossil molecules.”

The oldest samples with the biomarker are from the Barney Creek Formation in Australia and are 1.64 billion years old. The rock record of the next 800 million years yielded only fossil molecules of primitive eukaryotes before the molecular signatures of modern eukaryotes first appeared in the Tonian period. According to Nettersheim, “The Tonic Transformation looms as one of the most profound ecological turning points in the history of our planet.” Hallman adds that “both primitive stem groups and modern eukaryotic representatives such as red algae may have lived side by side for many hundreds of millions of years.” During this time, however, Earth’s atmosphere became increasingly enriched with oxygen—a metabolic product of cyanobacteria and the first eukaryotic algae—that would have been toxic to many other organisms. Later, global glaciations occurred on Earth with a snowball, and the protosterol communities largely died out. The last common ancestor of all living eukaryotes may have lived 1.2 to 1.8 billion years ago. Its descendants were probably better able to survive heat and cold as well as UV radiation and displaced their primordial relatives.

“Earth has been a microbial world for much of its history and has left few traces,” Nettersheim concludes. Research at ANU, MARUM and GFZ continues to search for the roots of our existence – the discovery of protosterols now brings us one step closer to understanding how our earliest ancestors lived and evolved. By imaging the ancient rocks with a laser coupled to an ultra-high-resolution mass spectrometer in MARUM’s globally unique Geomolecular Imaging Laboratory, Dr. Nettersheim and his international collaborators aim to zoom in on the cradle of eukaryotic life at unprecedented resolution to improve even more our understanding of our early ancestors in the future.

Reference: “The Lost World of Complex Life and the Late Emergence of the Eukaryotic Crown” by Jochen J. Brocks, Benjamin J. Nettersheim, Pierre Adam, Philip Schaefer, Amber J. M. Jarrett, Nur Guneli, Tarika Liyanage, Lennart M. van Maldegem, Christian Holman, and Janet M. Hope, 7 June 2023, Nature.
DOI: 10.1038/s41586-023-06170-w

Participating institutions:

• Research School of Earth Sciences, Australian National University, Canberra, Australia
• MARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
• Faculty of Geosciences, University of Bremen, Bremen, Germany
• University of Strasbourg, CNRS, Institute of Chemistry of Strasbourg, Strasbourg, France
• Northern Territory Geological Survey, Darwin, Australia
• German Research Center for Geosciences (GFZ), Potsdam, Germany

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