Paper Number: 822
Archean life on land
Retallack, G.J.1
1Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403, USA
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Newly discovered alluvial paleosols in the 3.0 Ga Farrel Quartzite of Western Australia are thin with organic surface (A horizon) and sulfate-rich subsurface (By) horizons, like soils of the Atacama Desert of Chile, Dry Valleys of Antarctica, 3.4-3.5 Ga paleosols of the Strelley Pool and Panorama Formations (Fig. 1), and 3.7 Ga paleosols of Mars [1]. Farrel Quartzite paleosols also contain a variety of microfossils, permineralized by silica in a way comparable with another famous terrestrial locality, the Devonian Rhynie Chert [2]. Five microfossil morphotypes in the Farrel Quartzite [3] each have distinctive carbon isotopic compositions, and include a variety of spheroidal cells (Archaeosphaeroides) as well as distinctive large spindles (cf. Eopoikilofusa). Cell-specific carbon isotopic analyses of the Farrel Quartzite microfossils [4] and unusually abundant sulfate for a likely anoxic atmosphere allow interpretation of these morphotypes as a terrestrial community of actinobacteria, purple sulfur bacteria, and methanogenic Archaea. Communities of anaerobic photosynthetic sulfur bacteria promoting a distinctive acid sulfate style of weathering, were widespread on land before driven underground by the Great Oxidation Event at around 2.4 Ga.
Figure 1: Polished slab of complete Jurl paleosol from 3.5 Ga Panorama Formation in Panorama Portal, north of Dresser Mine, Pilbara region, Western Australia. Bedded sandstone sharply overlies the massive and sand-crystal-rich paleosol above trough cross-bedded sandstone.
References:
[1] Retallack GJ (2014) Geology 42:755-758.
[2] Retallack GJ (2014) Palaeobotanist 63:1-15.
[3] Sugitani K et al. (2007) In: Stromatolites: interaction of microbes with sediments, Springer, Berlin, 117-132.
[4] House C et al. (2013) Geology 41:651-654.