Microbially influenced formation of 2,724-million-year-old stromatolites

Abstract

Nanoscale evidence suggests that the Tumbiana Formation stromatolites in Australia were influenced by microbial activity. In the stromatolites, clusters of organic globules are closely associated with 2,724-million-year-old aragonite crystals. Laminated accretionary carbonate structures known as stromatolites are a prominent feature of the sedimentary record over the past 3,500 Myr (ref. 1). The macroscopic similarity to modern microbial structures has led to the inference that these structures represent evidence of ancient life1,2. However, as Archaean stromatolites only rarely contain microfossils, the possibility of abiogenic origins has been raised2. Here, we present the results of nanoscale studies of the 2,724-Myr-old stromatolites from the Tumbiana Formation (Fortescue Group, Australia) showing organic globule clusters within the thin layers of the stromatolites. Aragonite nanocrystals are also closely associated with the organic globules, a combination that is remarkably similar to the organo-mineral building blocks of modern stromatolites3,4,5. Our results support microbial mediation for the formation of the Tumbiana stromatolites, and extend the geologic record of primary aragonite by more than 2,300 Myr (ref. 6).