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Article Dans Une Revue (Article De Synthèse) Nature Année : 2023

Lost world of complex life and the late rise of the eukaryotic crown

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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 (~1,600 to 800 million years (Ma) ago) and an absence of steranes, the molecular fossils of eukaryotic membrane sterols 1,2. This scarcity of eukaryotic remains is difficult to reconcile with molecular clocks that suggest that the last eukaryotic common ancestor (LECA) already emerged ~1200 to >1,800 Ma ago. LECA, in turn, must have been preceded by stem-group eukaryotic forms by several hundred million years. We report the discovery of abundant protosteroids in sedimentary rocks of mid-Proterozoic age. These primordial compounds remained unnoticed because their structures represent early intermediates of the modern sterol biosynthetic pathway, as famously 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 ~800 Ma ago and that likely comprised ancient protosterol-producing bacteria and deep-branching stem group eukaryotes. Modern eukaryotes started to rise in the Tonian period (1,000 to 720 Ma), fuelled by the proliferation of red algae (rhodophytes) by ~800 Ma. This ‘Tonian Transformation’ emerges as one of the most profound ecological turning points in our planet’s history.
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hal-04273175 , version 1 (07-11-2023)

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Jochen J Brocks, Benjamin J Nettersheim, Pierre Adam, Philippe Schaeffer, Amber J M Jarrett, et al.. Lost world of complex life and the late rise of the eukaryotic crown. Nature, 2023, 618 (7966), pp.767-773. ⟨10.1038/s41586-023-06170-w⟩. ⟨hal-04273175⟩
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