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The development of isotopic age determination methods and stable isotopic tracers to paleo-climate investigations, including oxygen (δ18O), sulphur (δ33S) and carbon (δ13C), integrated with Sedimentological records and organic and biological proxies studies, allows vital insights into the composition of early atmosphere–ocean-biosphere system, suggesting low atmospheric oxygen, high levels of greenhouse gases (CO2, CO, CH4 and likely H2S), oceanic anoxia and high acidity, limiting habitats to single-cell methanogenic and photosynthesizing autotrophs. Increases in atmospheric oxygen have been related to proliferation of phytoplankton in the oceans, likely about ~2.4 Ga (billion years-ago) and 0.7–0.6 Ga. The oldest recorded indirect traces of biogenic activity are provided by dolomite and banded iron formation (BIF) from ~3.85 Ga-old Akilia and 3.71–3.70 Ga Isua greenstone belt, southwest Greenland, where metamorphosed banded ironstones and dolomite seawater-like REE and Y signatures (Bolhar et al. Earth Planet Sci Lett 222:43–60, 2004; Friend et al. Contrib Miner Petrol 183(4):725–737, 2007) were shown to be consistent with those of sea water (Nutman et al. Precamb Res 183:725–737, 2010). Oldest possible micro-fossils occur in ~3.49 Ga black chert in the central Pilbara Craton (Glikson. Aust J of Earth Sci 55:125–139, 2008; Glikson. Icarus 207:39–44, 2010; Duck et al. Geochim Cosmochim Acta 70:1457–1470, 2008; Golding et al. Earliest seafloor hydrothermal systems on earth: comparison with modern analogues. In: Golding S, Glikson MV (eds) Earliest life on earth: habitats, environments and methods of detection. Springer, Dordrecht, pp 1–15, 2010) and in 3.465 Ga brecciated chert (Schopf et al. Precamb Res 158:141–155, 2007). Possible stromatolites occur in ~3.49 and ~3.42 carbonates. The evidence suggests life may have developed around fumaroles in the ancient oceans as soon as they formed. The evidence indicates extended atmospheric greenhouse periods interrupted by glacial periods which led to an increase in oxygen solubility in water, with implications for enhanced life. Intermittent volcanic eruptions and asteroid and comet impacts, representing continuation of the Late Heavy Bombardment as recorded on the Moon, resulted in major crises in biological evolution. |
