This multidisciplinary proposal has the objective to enhance our knowledge on the early steps of the evolution of life on Earth by providing a foundation for better deciphering the molecular fossil record as well as the geochemical signals hidden in ancient rocks. Based on the multiscale and multitechnique study of morphologically preserved microorganisms fossilized within ancient siliceous nodules, I propose to chronologically reconcile the evolution of metabolisms of life forms during the Precambrian with the variation of (sea)water paleo-temperatures registered by the silica matrix in which the investigated organic microfossils are embedded.Spatially-resolved information on fossil organic constituent speciation and their structural relationships with the silica matrix will be obtained at the nanometer scale using a unique combination of spectroscopy and microscopy techniques, notably including STXM and TEM. Crucial information on paleo-metabolisms will be obtained from NanoSIMS experiments by measuring the stable H-C-N-S isotope composition of the investigated fossilized objects at the scale of individual cells. In parallel, laboratory experiments will be conducted to better assess the potential isotopic and molecular evolution of organic molecules during the fossilization process. Estimations of water paleo-temperatures – likely corresponding to oceanic paleo-temperatures – will be achieved based on the distribution of the silicon and oxygen isotopic composition of silica closely associated to the fossil cells, measured at the very high spatial resolution of the NanoSIMS. Furthermore, the study of natural proxies will provide a more profound understanding of the significance of the temperature registered by the isotopic compositions of Precambrian cherts. In addition to radically change scientific ideas about Precambrian Paleontology, the technical and scientific developments resulting from this work will be broadly applicable and serve numerous communities.