Agradecimentos: The authors thank the University of Brasília, Nexa Resources and the geologist Bruno Baptistella for the support in the field trip; the Brazilian Synchrotron Light Laboratory (LNLS) for the facilities (µ-XRF, µ-XEOL, and XANES, proposals 20150076, 20160140 and 20180687) and Carnauba beamline (XANES, proposal 20210014); the microXAS beamline at Swiss Light Source (SLS, proposal 20190823); the Earth and Planets Laboratory at the Carnegie Institution of Science (Washington, DC) for the availability of the Raman spectrometer and EPMA microprobe. We also thank Dr. Silvio Y. Onary Alves (USP) for some clarification on terms and concepts about biological evolution. Brazilian Federal Agency for Support and Evaluation of Graduate Education—CAPES and the PDSE Program for the financial support, and scholarship in the beginning of the study; National Council for Scientific and Technological Development—CNPq Research Productivity Grants (310817/2020-0, 310,890/2021-7 and 303527/2017–0) and the São Paulo Research Foundation—FAPESP grants 2016/20927-0 and 2016/06114-6 (for funding the field trips to collect the samples), 2020/02537-5 and 2021/05083-8 for funding analysis and fellowship for this project, and 2015/21810-6 scholarship; the French National Research Agency in the framework of the Investissements d’Avenir program (ANR-15IDEX-02) Ver menos

Abstract: Deciphering the evolution of ecological interactions among the metabolic types during the early diversification of life on Earth is crucial for our understanding of the ancient biosphere. The stromatolites from the genus Conophyton cylindricus represent a datum for the Proterozoic (Meso to Neoproterozoic) on Earth. Their typical conical shape has been considered a result of a competition between microorganisms for space, light and nutrients. Well-preserved records of this genus from the "Paleontological Site of Cabeludo", Vazante Group, São Francisco Craton (Southern Brazil) present in situ fossilized biofilms, containing preserved carbonaceous matter. Petrographic and geochemical analyses revealed an alternation between mineral laminae (light grey laminae) and fossilized biofilms (dark grey laminae). The dark grey laminae comprise three different biofilms recording a stratified microstructure of microbial communities. These three biofilms composing the dark grey laminae tend to be organized in a specific pattern that repeats through the stromatolite vertical section. Iron and manganese are distributed differently along the dark and light grey laminae; X-ray absorption and luminescence data showed possible different areas with authigenic iron and iron provided from diagenetic infiltration. Cryptocrystalline apatite in the lowermost biofilms in each dark grey laminae may suggest past metabolic activity of sulfide-oxidizing bacteria. These findings suggest that the microorganisms reached a complex metabolic diversification in order to maintain an equilibrium situation between the three different biofilms along the vertical section of the structures, thus benefiting the whole microbial community. This means that the stromatolites from the Conophyton genus may have formed as a result of a greater complexity of interactions between microorganisms, and not only from competition between photosynthesizers Ver menos