This review presents 30 years of integrated geoscience data and modern analogue studies for the well-preserved, stromatolite-bearing lower chert member of the c. 3.48 Ga Dresser Formation (DF: Pilbara Craton, Australia), widely considered as the best, oldest evidence for life on Earth. Discovered in the late 1970s, subsequent detailed geological and hyperspectral mapping of the entire outcrop area has been augmented by scientific drilling campaigns (2007, 2019) to investigate primary structures and compositions unaffected by surface oxidation. Results from stratigraphic sections integrated with mapping, structural and alteration studies demonstrate that sedimentation was contemporaneous with voluminous hydrothermal fluid flow, epithermal-style alteration of footwall basalts, and listric growth faulting within an active, piecemeal-type volcanic caldera (Nijman et al., 1998; Van Kranendonk et al., 2008, 2019; Tadbiri and Van Kranendonk, 2020; Caruso et al., 2021). The basin evolved from deep, to shallow water - including emergent - conditions, and back to deep water, reflecting magmatic inflation and caldera subsidence. Emergence was accompanied by deposition of siliceous hot spring sinter (including geyserite and terracettes), and fluvial and lacustrine facies (Djokic et al., 2017, 2021). Bedded siderite-chert couplets with negative δ13Ccarb values, aragonite evaporative crystal splays, and Ba-Zn enrichments were deposited from evaporatively-concentrated seawater enriched by hydrothermal fluids during alternating wet season-dry season in a closed volcanic caldera basin, with analogues in East African rift lakes. Demonstrably biogenic domal, columnar, coniform and stratiform stromatolites flourished on the shoreline of the caldera lake, whereas small bushy microbialites inhabited hot spring deposits (Baumgartner et al., 2019; Van Kranendonk et al., 2019). 20 cm to 6 m thick intervals of repeated, coarse, upward-pointing barite crystals that cut into overlying, bedded pyrite-dolomite-chert sediment with/without stromatolites are analogous with textures in modern sabkhas where sulfate crystallisation via evaporation occurs in unlithified dolomite (+pyrite + organic matter) muds beneath microbial mats (Bontognali et al., 2010).

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Van Kranendonk MJ et al. 2019. In: Van Kranendonk MJ, Bennett V, Hoffmann E (eds.), Earth’s Oldest Rocks, 2nd Ed. Elsevier, USA, p. 985-1006.