| Summary: | In press. International audience Conditions at the surface of the young (Hadean and early Archean) Earth were suitable for the emergence and evolution of life. After an initial hot period, surface temperatures in the late Hadean may have been clement beneath an atmosphere containing greenhouse gases over an ocean-dominated planetary surface. Plate tectonics probably started early, and had produced voluminous continental crust by late Hadean, but ocean volumes may have been sufficient to submerge much of this crust. In the Hadean and early Archean, hydrothermal systems around abundant komatiitic volcanism may have provided suitable sites for hosting the earliest living communities, and for the evolution of key enzymes. Evidence from the Isua belt, Greenland, suggests life was present by 3.8 Ga ago, and by mid-Archean the geological record both in the Pilbara in Western Australia and the Barberton Mountain Land in South Africa shows that microbial life was abundant, probably using anoxygenic photosynthesis. By late Archean oxygenic photosynthesis had evolved, transforming the atmosphere and permitting the evolution of eukaryotes.
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