They discovered a “lost world” of ancient ancestors in billion-year-old rocks

At least 1.6 billion years ago, microscopic organisms lived in water, whose molecular fossils have been found in rocks from that time and may be the oldest traces of our lineage.

The discovery of this microscopic “lost world,” published today in Nature, could change our understanding of our earliest ancestors.

All organisms with eukaryotic cells (animals, plants and fungi, membrane-enclosed DNA) had a first common ancestor known as LECA, which lived 1.2 billion years ago, but must have been preceded by other forms of eukaryotes. .

A team of Australian, French and German researchers has found abundant protosteroids in Proterozoic (2.5 billion to 542 million years ago) rocks, primordial compounds that had previously been overlooked as fossil evidence of early life.

Those biomarker signatures point to the presence of previously unknown species that dominated complex life on Earth and lived at least a billion years before the appearance of any animal or plant.

A team led by Jochen Brocks of the Australian National University (AUN) has discovered the existence of these microscopic organisms that are part of eukaryotic organisms, commonly named “protosterol biota”.

“Molecular remains of protosterol biota found in 1.6-billion-year-old rocks appear to be the oldest remnants of our own lineage: they lived before LECA,” said co-author Benjamin Nettersheim of the University of Bremen in Germany. .

These organisms, which flourished from about 1.6 billion years ago to about 800 million years ago, were abundant in marine ecosystems around the world and may have shaped ecosystems for much of Earth’s history.

Although it is not known what they looked like, they would have been more complex and presumably larger than bacteria, Brocks pointed out in his university’s report: “We believe they may have been the first predators on Earth to hunt and devour bacteria.”

They differ from complex eukaryotic life (animals, plants and algae) in their cellular structure and perhaps their metabolism, which adapted to a world with much less oxygen in the atmosphere, the center said. German Research Center for Geosciences (GFZ).

It is also not known when these ancient organisms went extinct, although it points to a tonic period, when more advanced eukaryotic organisms such as fungi and algae began to flourish.

“For our mammalian ancestors to grow large and abundant, the protosterol biota had to die out a billion years ago to make room for modern eukaryotes, just as the dinosaurs went extinct,” Brocks said.

To make the discovery, the researchers analyzed fossil lipid molecules known as protosteroids, which were unearthed from a 1.6-billion-year-old sedimentary rock that formed on the sea floor near Australia from the mid-Proterozoic.

The molecules had a primordial chemical composition, pointing to the existence of primitive complex organisms that had evolved and died out before the LECA. Without these biomarkers, “we wouldn’t have known that the protosterol biota existed, and scientists have overlooked these molecules for four decades because they don’t fit into conventional molecular search images,” says Nettersheim.

But once they knew what they were looking for, they found that dozens of other rocks, taken from billion-year-old streams around the world, “extruded similar fossil molecules.”

1958 Nobel Prize in Medicine Konrad Bloch predicted the existence of primitive molecules of this type in 1994, so these findings may prove him right.

However, he assumed that these intermediate protomolecules would never be found because they would not survive in the geological record, although this research now indicates that this is not the case and suggests that the remains of protosteroids may have remained in the rock for over a billion years.