Traces of early Life from the Barberton Greenstone Belt, South Africa

We review the evidence for traces of Paleoarchean (3.47–3.2 Ga) life in the Barberton Greenstone Belt (BGB), South Africa. Morphological, organic, geochemical, isotopic, and mineralogical biosignatures are preserved in massive and stratiform volcano-sedimentary cherts, in hydrothermal and chemical sedimentary rocks, and in quartz-rich sandstones. The well-preserved lithologies of the BGB record a broad diversity of features interpreted as the remnants of anaerobic life forms, including chemotrophs, benthic phototrophs, and possible planktonic organisms. Inferred photosynthetic fossils include planar to low-amplitude, finely laminated microbial mats and stromatolites from marine and terrestrial settings. Rarely preserved, putative, filamentous microfossils are very small compared with present-day phototrophs. Putative chemotrophic fossils are more enigmatic and generally restricted to nutrient-rich hydrothermal environments. Relatively large (up to some hundreds of microns) lenticular and spherical carbonaceous microfossils are interpreted as possible planktonic forms. Many proposed microfossils are of simple morphology and poorly preserved, thus it is difficult to completely discount abiogenic mechanisms for their formation.