Billion-year-old rocks show clues of ancient life

A recent finding of organic molecules in ancient rocks in Australia helps elucidate the early history of eukaryotes, revealing that this group was already common more than a billion years ago, according to a new research.

Eukaryotes are known to date back 2 billion years, but scientists assumed that they only became ubiquitous around 800 million years ago, said Dr. Benjamin Nettersheim, one of the co-first authors of the research published in Nature.

However, newfound traces of molecules possibly produced by eukaryotes are up to 1.6 billion years old, which indicates “that early eukaryotes were already ecologically important for all this time,” said Nettersheim, who is a postdoctoral researcher in geobiology at the MARUM Center for Marine Environmental Sciences at the University of Bremen in Germany. “We just didn’t see their traces until now. They’ve sort of been hiding in plain sight.”

The evidence of these ancient eukaryotes took the form of biological substances that they created. Modern eukaryotes create a range of distinctive biomolecules, including cholesterols.

Cholesterol is an organic molecule, a naturally occurring steroid. Too much of it may create health concerns like blocked arteries, yet it’s a crucial component of cell membranes for practically all contemporary eukaryotes. Cholesterols are “really important for a large number of physiological functions, and because they are part of the cell membrane, organisms produce relatively much of these kinds of molecules,” Nettersheim added.

In the latest research, Nettersheim and another co-first author, Jochen Brocks, uncovered a molecule linked to cholesterol that appeared to validate a decades-old idea about the development of eukaryotes.

Exploring the domain of ancient molecules uncovers a fascinating world where remnants of long-lost substances are found and examined, revealing insights into the distant past.

Scientist Konrad Bloch, who earned the Nobel Prize in Physiology or Medicine in 1964, found that while contemporary eukaryotes produce cholesterol, various intermediate chemical molecules occur. He argued that in the deep past, each of these intermediary molecules was a fully functioning end-product of early organisms’ metabolic processes. However, Bloch feared that no one would ever be able to locate fossil evidence to establish that early living forms generated these now-intermediate biomolecules.

Advances in biochemical analysis have enabled scientists to detect ancient molecules retained in the fossil record, especially in old rocks that have been largely undisturbed by geological processes.

In the new Nature research, Nettersheim and his colleagues, including Brocks, a professor of geobiology at the Australian National University, studied rocks from Australia’s Barney Creek Formation.

Previous investigations demonstrated that the Barney Creek rocks, which are more than 1 billion years old, contain remnants of ancient proteins. But “people never looked, really, for these primordial types of steroids in those kinds of rocks,” Nettersheim added.

Nettersheim, Brocks and their colleagues did chemical investigations of rocks from Barney Creek, seeking for the cholesterol precursors that Bloch hypothesized would have been generated by early eukaryotes.

“To our surprise, we actually found them in surprisingly high abundance, and everywhere we have biomarkers preserved in this time period, we also see these molecules,” Nettersheim stated. “We now can confirm the Bloch hypothesis.”

The existence of these protosteroids implies that early eukaryotes were evolved to a planet considerably different from present Earth. There is significantly more oxygen in the atmosphere now than there was 1.6 billion years ago, and the proto-steroid molecules created by these early eukaryotes needed less oxygen to make than cholesterols.

“It might be an advantage to use these more primordial sterols,” Nettersheim remarked. The early eukaryotes “were already perfectly adapted to the prevailing ecological conditions.”

Dr. Susannah Porter, a professor and head of the department of earth science at the University of California, Santa Barbara, stated, “What I really like about this study is thinking about recognizing that biosynthetic pathways evolve as well.”

However, Porter, who was not involved in the work, is hesitant in stating that the chemicals revealed in this study were actually generated by early eukaryotes as opposed to other ancient species.But Dr. Roger Summons, a professor of geobiology at the Massachusetts Institute of Technology who was also not involved with the work, termed it “one of the more interesting organic geochemistry studies that I have seen in many a year.”

“Konrad Bloch would have been delighted had he lived to see this because Brocks and colleagues have elegantly confirmed his prediction that biosynthetic precursors to cholesterol reflect biochemistry’s search for functional optimization,” Summons said.

Meanwhile, Nettersheim said the next step for him and his colleagues is to further explore the environment inhabited by these ancient living forms by blasting lasers at a tiny slice of rock and utilizing the information about how the light bounces off it to map the diverse chemical components there.

“We hope that this will help us constrain a lot further, where, when, under which conditions our early eukaryotic ancestors thrived,” he stated