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On the age of eukaryotes: evaluating evidence from fossils and molecular clocks. in Blondes in Venetian Paintings, the Nine-Banded Armadillo, and Other Essays in Biochemistry 14–36 (Yale Univ. Integrated genomic and fossil evidence illuminates life’s early evolution and eukaryote origin. 1.1-Billion-year-old porphyrins establish a marine ecosystem dominated by bacterial primary producers. This ‘Tonian transformation’ emerges as one of the most profound ecological turning points in the Earth’s history.īutterfield, N.
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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. 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. These primordial compounds had previously remained unnoticed because their structures represent early intermediates of the modern sterol biosynthetic pathway, as predicted by Konrad Bloch 4. Here we report the discovery of abundant protosteroids in sedimentary rocks of mid-Proterozoic age. LECA, in turn, must have been preceded by stem-group eukaryotic forms by several hundred million years 3. This scarcity of eukaryotic remains is difficult to reconcile with molecular clocks that suggest that the last eukaryotic common ancestor (LECA) had already emerged between around 1,200 and more than 1,800 million years ago.
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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) and an absence of steranes, the molecular fossils of eukaryotic membrane sterols 1, 2.
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Eukaryotic life appears to have flourished surprisingly late in the history of our planet.
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