Metabolically diverse primordial microbial communities in Earth's oldest seafloor-hydrothermal jasper

The oldest putative fossils occur as hematite filaments and tubes in jasper-carbonate banded iron formations from the 4280- to 3750-Ma Nuvvuagittuq Supracrustal Belt, Quebec. If biological in origin, these filaments might have affinities with modern descendants; however, if abiotic, they could indicate complex prebiotic forms on early Earth. Here, we report images of centimeter-size, autochthonous hematite filaments that are pectinate-branching, parallel-aligned, undulated, and containing Fe2+-oxides. These microstructures are considered microfossils because of their mineral associations and resemblance to younger microfossils, modern Fe-bacteria from hydrothermal environments, and the experimental products of heated Fe-oxidizing bacteria. Additional clusters of irregular hematite ellipsoids could reflect abiotic processes of silicification, producing similar structures and thus yielding an uncertain origin. Millimeter-sized chalcopyrite grains within the jasper-carbonate rocks have S-34- and S-33-enrichments consistent with microbial S-disproportionation and an O-2-poor atmosphere. Collectively, the observations suggest a diverse microbial ecosystem on the primordial Earth that may be common on other planetary bodies, including Mars.

Automated summary

This study reports the discovery of putative fossils in jasper-carbonate banded iron formations from the Nuvvuagittuq Supracrustal Belt in Quebec. These fossils, which are hematite filaments and tubes, have characteristics that suggest both biological and abiotic origins. The presence of mineral associations, resemblance to younger microfossils, and similarities to modern Fe-bacteria indicate a possible biological origin. On the other hand, the presence of abiotic structures and the enrichment of certain minerals suggest complex prebiotic forms. These findings provide insight into the diversity of microbial ecosystems on early Earth and the potential for similar ecosystems on other planetary bodies.