Abstract EANA2025-63

The Ediacaran period (635–541 My ago) marks a crucial phase in Earth's history, characterized by the emergence of the first large, complex multicellular life forms, the rise of soft-bodied Ediacaran biota, increased oxygen levels, and ecological innovations that set the stage for the Cambrian Explosion and the rapid diversification of animal life. Reconstructing the paleoecology of the Ediacaran period contributes to a better understanding of the causes and processes that led to environmental changes that triggered such significant biological transformations, with implications for the reconstruction of early life and astrobiology. Yet, biogeochemical evidence of this type of communities and activity in different terrestrial environments are scarce.

In the lack of well-preserved hard-shelled organisms and body fossils, the aid of chemical fossils is crucial for reconstructing the paleobiology of such an important evolutionary period, where molecular or isotopic signatures provide key information about their origin, biological sources and synthetic pathways. Notably, the organic compounds derived from cell membranes (i.e. lipids) are compelling biomarkers to trace ancient life given their ubiquity in terrestrial life and their chemical resistance. Their hydrocarbon skeletons are able to withstand over geological timescales while retaining enough characteristic features to recognize biogenicity up to billion years ago.

The Ouarzazate Supergroup in the Moroccan Anti-Atlas represents a significant geological formation from the Ediacaran, where carbonate stromatolites have been found in the basin of an ancient alkaline lake. The Amane-n´Touhart formation offers unique insights into the paleoenvironmental conditions and microbial life during the late Precambrian through the study of their abundant stromatolites. These organo-sedimentary structures are among the oldest evidence of life on Earth (at least over 3.5 Gy old) and represent interactions between biosphere and geosphere that provide compelling astrobiological targets for detecting life on planetary bodies. Yet, little is known on the preservation of molecular fossils in stromatolites from the Ediacaran.

Here we search for lipidic fingerprints of life in three stromatolites from the Amane-n'Tourhart formation. Their molecular analysis revealed the presence of syngenic n-alkanes, isoprenoids, hopanes and steranes, with stable-carbon isotopic composition reflecting the use of the Calvin–Benson–Bassham cycle. This was consistent with the detection of hopanes associated with oxygenic cyanobacteria (i.e. 2α-methylhopanes) and steranes indicative of eukaryotic phototrophs (algae). Other steranes suggested the presence of biomass from fungi and early animals, while the molecular distribution of steranes revealed a marine fingerprint compatible with a Ediacaran scenario. These findings align with fossil evidence of Ediacaran algae, sponges, and fungi, reinforcing the biological diversity of the period.

The combination of isotopic signatures, molecular distributions, and contamination controls supports the indigenous and syngeneic nature of the detected biomarkers. This study highlights the value of lipid biomarkers in reconstructing ancient ecosystems and contributes to our understanding of the environmental and biological transitions leading up to the Cambrian Explosion. As far as we know, this is the first study that provides molecular and isotopic fingerprints of life in this stromatolitic formations from the Ediacaran period from Morocco with high value for early life and astrobiology.