Ancient steroid molecules found in 1.64 billion years

Aug 30, 2023

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Much before ancient humans, Earth was largely populated with microbial life forms in prehistoric times. And now, scientists have traced back an ancient record of the eukaryotic life on the Earth.

To begin, Eukaryotes are a diverse group of organisms with nuclei in their cells. It is a broad term that refers to the "kingdom of life," which includes all animals, plants, and algae. Eukaryotes are estimated to have been around for more than 2 billion years.

A team of researchers has discovered a unique molecular record of eukaryotes. Finding early eukaryotic fossils may aid in better understanding the conditions underlying the evolution of complex forms of life.

In ancient rocks, they discovered a new type of steroid, which are biologically active organic compounds. It's referred to as protosteroids.

This discovery suggests that complex eukaryotic life was abundant throughout the Earth's Middle Ages. It even verifies Nobel Laureate Konrad Bloch's hypothesis of the presence of ancient steroid compounds.

Fossils of ancient Eukaryotes organisms are scarce, but researchers posited that there could be some traces of molecular fossils in rocks.

The researchers discovered protosteroids molecules in mid-Proterozoic sedimentary strata in Australia's Barney Creek Formation. These rocks date back 1.64 billion years.

The Australian National University

The findings supported early eukaryotes' dominance in aquatic habitats from at least 0.8 to 1.6 billion years ago.

"Almost all eukaryotes biosynthesize steroids, such as cholesterol that is produced by humans and most other animals," said Benjamin Nettersheim from MARUM, University of Bremen, and one of the first authors of this study, in an official release.

Nettersheim adds, "Due to potentially adverse health effects of elevated cholesterol levels in humans, cholesterol doesn't have the best reputation from a medical perspective. However, these lipid molecules are integral parts of eukaryotic cell membranes where they aid in a variety of physiological functions. By searching for fossilized steroids in ancient rocks, we can trace the evolution of increasingly complex life."

But how did the scientists find this new type of molecule in ancient rocks? It is, after all, a rather difficult process.

The researchers began by experimenting with several strategies to convert known modern steroids to their fossilized counterparts. This improved their grasp of what to look for.

"Once we knew our target, we discovered that dozens of other rocks, taken from billion-year-old waterways across the world, were oozing with similar fossil molecules," said Jochen Brocks, first author of this study from the Australian National University (ANU).

After identifying the target, the scientists utilized a laser to peer into ancient rocks, while an ultra-high resolution mass spectrometer was employed to detect the molecules.

The authors highlight that metabolic products of cyanobacteria and the earliest eukaryotic algae began to fill the Earth's atmosphere with oxygen about hundreds of millions of years ago.

Soon after the cold "Snowball Earth" event occurred and the protosterol communities started to vanish from the globe. The last common ancestor of all living eukaryotes may have lived 1.2 to 1.8 billion years ago.

It is possible that the last common ancestor of all extant eukaryotes lived 1.2 to 1.8 billion years ago. Its descendants evolved to adjust to heat, cold, and UV rays — and eventually displaced their ancestors.

The findings have been reported in the journal Nature.

Study abstract:

Eukaryotic life appears to have flourished surprisingly late in the history of our planet. This view is based on the low diversity of diagnostic eukaryotic fossils in marine sediments of mid-Proterozoic age (around 1,600 to 800 million years ago) andan absence of steranes, the molecular fossils of eukaryotic membrane sterols. This scarcity of eukaryotic remains is difficult to reconcile with molecular clocksthat suggest that the last eukaryotic common ancestor (LECA) had already emerged between around 1,200 and more than 1,800 million years ago. LECA, in turn, must have been preceded by stem-group eukaryotic forms by several hundred million years3. Here we report the discovery of abundant protosteroids in sedimentary rocks of mid-Proterozoic age. These primordial compounds had previously remained unnoticed because their structures represent early intermediates of the modern sterol biosynthetic pathway, as predicted by Konrad Bloch4. The protosteroids reveal an ecologically prominent ‘protosterol biota’ that was widespread and abundant in aquatic environments from at least 1,640 to around 800 million years ago and that probably comprised ancient protosterol-producing bacteria and deep-branching stem-group eukaryotes. Modern eukaryotes started to appear in the Tonian period (1,000 to 720 million years ago), fuelled by the proliferation of red algae (rhodophytes) by around 800 million years ago. This ‘Tonian transformation’ emerges as one of the most profound ecological turning points in the Earth's history.