Fig. 1: Analogue sedimentary sample collection.

A A microbialite ( ~ 2800-year-old) was sampled in Alchichica, Mexico, an alkaline crater lake with high concentrations of NaCl and Na₂CO₃. These microbialites formed through microbially mediated carbonate precipitation and remain submerged in shallow waters, where they continue to accrete carbonate minerals and support diverse microbial communities. B A stromatolite ( ~ 541 Ma) was sampled from this field in Morocco, which is part of the Mançour Group within the Ouarzazate Supergroup (Anti-Atlas region). This carbonate stromatolite formation (400 m × 500 m) developed in a shallow marine environment and was later buried beneath volcanic and volcaniclastic sediments. Tectonic uplift and erosion during the late Paleozoic and Cenozoic exposed the stromatolites, which are primarily composed of limestone (CaCO₃) and dolomite (CaMg(CO₃)₂), formed by cyanobacteria-driven sediment trapping and binding before the Cambrian explosion. C Carbonate samples ( ~ 2930 Ma) from drilled cores extracted from a depth of 133 m, in the carbonate formation from the Bridget Lake area. These samples consist of dolomite (CaMg(CO₃)₂). They precipitated in an open marine environment as dissolved calcium and bicarbonate ions reached saturation. Cyanobacteria likely influenced this process through photosynthesis, which removed CO₂, increased carbonate alkalinity, and promoted mineral precipitation. D Detailed view of a carbonate formation fragment ( ~ 2930 Ma). Small portions (4–5 g) were extracted from fragments of each sample type for further analysis.