Remains of an extinct world of living organisms have been discovered

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Artist’s imagination of a group of primitive eukaryotes from the “Protosterol Biota” living on a bacterial mat on the ocean floor. Based on molecular fossils, the Protosterol Biota organisms lived in the oceans from about 1.6 to 1.0 billion years ago and are our oldest known ancestors. Credit: Organized on MidJourney by TA 2023

Newly discovered biomarker signatures point to a whole group of previously unknown organisms that dominated complex life on Earth about a billion years ago. They differed from the complex life of eukaryotes as we know them, such as animals, plants, and algae in their cellular structure and potential metabolism, which were adapted to a world with much less oxygen in the atmosphere than it does today.

An international team of researchers, including GFZ geochemist Christian Hollmann, is now reporting this breakthrough in the field of evolutionary geobiology in the journal. nature.

And it turns out that previously unknown “elemental steroids” were surprisingly abundant throughout the Middle Ages of the Earth. Primordial molecules were produced at an early stage in the complexity of eukaryotes – extending the current record of fossil sterols beyond 800 and even 1,600 million years ago. Eukaryotes is a term given to the kingdom of life including all animals, plants, and algae and is separated from bacteria by having a complex cellular structure that includes a nucleus, as well as a more complex molecular mechanism.

“The most important implication of this discovery is not simply an extension of the current molecular record of eukaryotes,” Holman says, “given that the last common ancestor of all modern eukaryotes, including us humans, was likely able to produce ‘regular’ modern sterols.” Chances are high that the eukaryotes responsible for these rare signatures belong to the trunk of the phylogenetic tree.”

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An unprecedented glimpse into a lost world

This “stump” represents the common ancestral lineage that was the precursor to all still living branches of eukaryotes. Its representatives are long extinct, but details of their nature may shed more light on the circumstances surrounding the evolution of complex life.

Although more research is needed to assess what percentage of protosteroids may have a rare bacterial source, the discovery of these new molecules not only reconciles the geological record of traditional fossils with that of fossil fat molecules, but gives a rare and unprecedented glimpse into the world. lost from the old life.

The competitive demise of stem-group eukaryotes, marked by the first appearance of modern fossil stromals about 800 million years ago, may reflect one of the most enduring events in the evolution of increasingly complex life.

Artist’s silhouette of a primitive eukaryotic “Protosterol Biota” on the ocean floor. Based on molecular fossils, the Protosterol Biota organisms lived in the oceans from about 1.6 to 1.0 billion years ago and are our oldest known ancestors. Credit: Organized on MidJourney by TA 2023

“Almost all eukaryotes synthesize vital steroids, like cholesterol produced by humans and most other animals,” adds Benjamin Nittersheim from the University of Bremen, first author of the study.

“Due to the potentially harmful health effects of high cholesterol levels in humans, cholesterol does not have the best reputation from a medical perspective. However, these lipid molecules are an integral part of eukaryotic cell membranes where they assist in a variety of physiological functions.” When Looking for Fossil Steroids In ancient rocks, we can trace the evolution of increasingly complex life.”

What the Nobel laureate thought is impossible

Nobel laureate Konrad Bloch had already speculated about such a biomarker in an article nearly 30 years ago. Bloch suggested that the short-lived intermediates in the modern biosynthesis of steroids may not always be intermediates.

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It was believed that lipid biosynthesis evolved in parallel with changing environmental conditions throughout Earth’s history. Unlike Bloch, who did not believe that such ancient media could be found, Nettersheim began looking for protosteroids in ancient rocks deposited at a time when such media would have been the final product.

But how do we find such molecules in ancient rocks? says Jochen Brooks, a professor at the Australian National University who co-first authors a new study with Nettersheim.

Scientists have overlooked these molecules for decades because they don’t fit into the typical picture of molecular research. “Once we knew our target, we discovered that dozens of other rocks, taken from billion-year-old waterways around the world, were exuding similar fossil particles.”

The oldest samples containing the biomarker are from the Barney Creek Formation in Australia and are 1.64 billion years old. The rock record for the next 800 million years yielded only fossil particles of primitive eukaryotes before the molecular signatures of modern eukaryotes first appeared in the Tonian period.

According to Nettersheim, “The Tonian Transformation is emerging as one of the most profound environmental tipping points in our planet’s history.” Holman adds that “both primitive stem groups and representatives of modern eukaryotes such as red algae may have lived side by side for hundreds of millions of years.”

However, during this time, the Earth’s atmosphere became increasingly rich in oxygen – a metabolic product of cyanobacteria and eukaryotic algae that would otherwise be toxic to many other organisms. Subsequently, “Snowball Earth” global glaciation occurred and the protosterol communities largely vanished. The last common ancestor of all living eukaryotes probably lived 1.2 to 1.8 billion years ago. It is likely that her descendants were better able to tolerate heat and cold as well as ultraviolet radiation and displaced their Neanderthal relatives.

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Since all stem-group eukaryotes became extinct long ago, we’ll never know for sure what most of our early relatives looked like, but technical efforts have created tentative renderings (see attached images), while primitive steroids may eventually shed more light on Biochemistry and lifestyle.

“Earth has been a microbial world for most of its history and has left few traces,” Nettersheim concludes. Research at ANU, MARUM and GFZ continues to trace the roots of our existence – and the discovery of protosterols now brings us closer to understanding how our early ancestors lived and evolved.

more information:
Jochen Brooks, A Lost World of Complex Life and the Late Emergence of the Eukaryotic Crown, nature (2023). DOI: 10.1038/s41586-023-06170-w.

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