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Early Life Traces, Evolution, and Implications for Astrobiology

Final Report Summary - ELITE (Early Life Traces, Evolution, and Implications for Astrobiology)

The objectives of the ELiTE ERC project focused on:
1) The identification of Early traces of life and their preservation conditions, in Precambrian rocks of established age
2) The characterization of their biological affinities, using innovative approaches comprising micro to nanoscale morphological, ultrastructural and chemical analyses of fossil and recent analog material
3) The determination of the timing of major steps in evolution. In particular, we aim to decipher two major and inter-related steps in early life evolution and the rise of biological complexity: the evolution of cyanobacteria, responsible for Earth oxygenation and ancestor of the chloroplast, and the evolution of the domain Eucarya.
4) The determination of causes of observed pattern of evolution in relation with the environmental context (oxygenation, impacts, glaciations, tectonics, nutrient availability in changing ocean chemistry) and biological innovations and interactions (ecosystems evolution).
To address these objectives, we characterized chemical and morphological biosignatures at the macro- to the micro-scale, and their mode of preservation, in Precambrian rocks and in modern analogs from extreme environments. We also studied the geological context locally (age, environments, redox conditions) and globally (climate, tectonics, metamorphism) to better constrain the co-evolution of Earth and Life. We combined high-resolution micropaleontology and geochemistry to decipher the paleoecology of the proterozoic biosphere.
The ELiTE project has characterized new biosignatures of early life, including cyanobacteria and eukaryotes, discovered new microfossil assemblages in Africa, Canada, China and Australia, and evidenced a different, earlier and more gradual, pattern of eukaryotic diversification. The team has discovered the oldest evidence for intracellular biomineralisation of iron in 1.9 Ga cyanobacteria, the oldest evidence for selective protist predation at 1.1 Ga, the oldest evidence for opisthokonts at 1-0,8 Ga, the oldest eclogite evidencing modern style plate tectonics around 2.2 Ga and opening and closure of an ocean-a Wilson cycle, and also contributed to the discovery of the oldest pigment porphyrin showing that cyanobacteria were main primary producers in mid-proterozoic oceans. Biological innovations and ecological interactions such as selective eukaryovory (protist eating protist), symbiosis (photosynthesis), multicellularity, and osmotrophy in early eukaryotes are proposed as drivers for eukaryotic diversification in mid-proterozoic redox stratified oceans, close to estuarine nutrient supply.
This work not only documented some of the first traces of life, the early evolution of life, including complex life (eukaryotes), and possible biosignatures useful for paleobiology and astrobiology, but also the changing habitability conditions of Earth that sustained life from (at least) its earliest traces in the Archean through the Proterozoic, and the interactions between the biosphere, the geosphere, and the atmosphere.