Archean tufted microbial mats and the Great Oxidation Event: new insights into an ancient problem

The macroscopic fossil record of the Archean consists solely of stromatolites and other microbialites, which seldom offer compelling clues to the identities of the organisms that formed them. Tufted microbial mats are an exception because their formation is known to require a suite of morphological and behavioural characteristics from which the behavioural and biological affinities of early microbialite-constructing microbes can be inferred. Here, the oldest yet reported convincing fossil tufted microbial mats are described and discussed in the context of other ancient and modern examples. Significantly, cyanobacteria dominate all known modern occurrences and may also have been the builders of ancient examples, the oldest of which predate by several hundred million years the earliest convincing cyanobacterial microfossils and most geochemical evidence for an oxygenated atmosphere.