The question of when the transition from prokaryotic to eukaryotic form occurred and when the first crown group eukaryotes appeared on earth is unresolved. The oldest known body fossils that can be positively assigned to the Eukaryota are acanthomorphic acritarchs from the 1.631 Gya Deonar Formation of India. These fossils can still be identified as derived post-nuclear eukaryotes with a sophisticated, morphology-generating cytoskeleton sustained by mitochondria. This fossil evidence indicates that endosymbiotic acquisition of alphaproteobacteria must have occurred before 1.6 Gya. Molecular clocks have also been used to estimate the last eukaryotic common ancestor, however these methods have large inherent uncertainty and give a wide range of dates. Reasonable results include the estimate of c. 1.8 Gya. A 2.3 Gya estimate also seems reasonable, and has the added attraction of coinciding with one of the most pronounced biogeochemical perturbations in Earth history, the early Palaeoproterozoic Great Oxygenation Event. The marked increase in atmospheric oxygen concentrations at that time has been suggested as a contributing cause of eukaryogenesis, inducing the evolution of oxygen-detoxifying mitochondria. Alternatively, the Great Oxidation Event might be a consequence of eukaryogenesis, and its impact on the export and burial of organic carbon.
the question of when the transition from prokaryotic to eukaryotic form occurred and when the first crown group eukaryotes appeared on earth is unresolved the oldest known body fossils that can be positively assigned to the eukaryota are acanthomorphic acritarchs from the 1631 gya deonar formation of india these fossils can still be identified as derived post-nuclear eukaryotes with a sophisticated morphology-generating cytoskeleton sustained by mitochondria this fossil evidence indicates that endosymbiotic acquisition of alphaproteobacteria must have occurred before 16 gya molecular clocks have also been used to estimate the last eukaryotic common ancestor however these methods have large inherent uncertainty and give a wide range of dates reasonable results include the estimate of c 18 gya a 23 gya estimate also seems reasonable and has the added attraction of coinciding with one of the most pronounced biogeochemical perturbations in earth history the early palaeoproterozoic great oxygenation event the marked increase in atmospheric oxygen concentrations at that time has been suggested as a contributing cause of eukaryogenesis inducing the evolution of oxygen-detoxifying mitochondria alternatively the great oxidation event might be a consequence of eukaryogenesis and its impact on the export and burial of organic carbon