Long before life exploded in diversity on the planet, the seas already housed discreet organisms, without shell or skeleton, of which there are almost no visible trace. However, certain clues buried in the oldest rocks begin to lift the veil over this enigmatic period. This is how new hypotheses emerge on the first animals on earth, no longer guided by bones but by the molecules themselves.
These steranes with 30 carbon atoms, almost absent from other living beings, already raised questions. But their rarity and the possibility of a non -biological origin left the door open to doubt. To support this track, the researchers continued their work for more than ten years. Over time, they have collected new samples in India, Siberia and elsewhere. Then they refined their methods in order to draw more precise results. Thanks to these efforts, another family of steranes appeared, even rarer than the first. This time these are molecules containing 31 carbon atoms, which are also found in certain current sponges.
What ancient steroids reveal to the first animals on earth
The new discovered biomarkers share a precise chemical structure with the sterols produced by several current species of demospons. In the laboratory, researchers have even synthesized eight C31 sterols to simulate their fossilization over millions of years. Only two of these compounds are found in Precambrian rocks, a result that pleads in favor of a biological origin and not a random transformation.
MIT, at the origin of this research published in the Proceedings of the National Academy of Sciences, underlines that these steranes cannot be explained either by algae or by unicellular microorganisms as the Rhizaria. The latter produce many sterols, but in tiny quantities and in configurations which do not correspond to the found molecules. As for the possibility of a natural chemical alteration of algae sterols, it is contradicted by the very selective distribution of the C31 steranes in sediments.
By crossing geological, biological and experimental data, scientists have shown that these compounds can only appear when sponges with the appropriate genes are present. Modern demosponges capable of producing these rare sterols present the same molecular profiles as those found in the southern rocks of Oman, dated from the ediacarian, more than 541 million years.
A promising track to go up the lifetime line
This discovery is not limited to a simple identification. It changes the framework in which the history of animal appearance is written. So far, most stories have placed the emergence of animal complexity during the Cambrian explosion, about 540 million years ago. However, the steranes found in the precambrian rocks indicate that forms of multicellular life, already animal, existed well before this date.
The study relayed in Popular Science highlights the potential of these fossil molecules to track down invisible life, that which has left neither imprint nor shell. As researchers are probe other deposits in the world, they hope to refine the chronology and perhaps discover other sole-speaking molecular clues. This approach based on sterols could become a central tool to map the beginnings of animal life on earth, by revealing the forgotten presences in the oldest sediments.
The fact that these steroids are still produced today by certain current sponges weaves a direct link between the primordial ocean and contemporary marine ecosystems. These molecules are going through time, unchanged, like a biochemical Ariane wire which connects the first animals on earth to the simplest forms of life still present in our seas.
With an unwavering passion for local news, Christopher leads our editorial team with integrity and dedication. With over 20 years’ experience, he is the backbone of Wouldsayso, ensuring that we stay true to our mission to inform.
