Advanced 2D-3D insights into Earth's oldest stromatolites (~3.5 Ga): prospects for the search for life on Mars

Paleoarchean stromatolites are among the oldest compelling evidence for life. Here, we present advanced 2D–3D reconstructions of the morphology, mineralogy, trace element geochemistry and taphonomy of permineralized stromatolites from the lowermost horizons of the ~3.5 Ga Dresser Formation, Pilbara, Western Australia. Rare earth element plus yttrium compositions suggest a restricted palaeodepositional setting influenced by marine influxes; this contrasts with other Dresser stromatolites, which developed around terrestrial hot springs. Mineral phase relationships and positive Eu anomalies denote syndepositional hydrothermal influence and silicification promoting high-fidelity microstructural preservation. Although no primary kerogen is preserved, numerous 2D–3D morphological characteristics denote a biogenic origin, including the onlap of sedimentary layers onto stromatolitic topography, fine-scale undulatory laminations, non-isopachous laminations with crestal thickening, laminoid fenestrae, and sub-vertical fabrics interpreted as microbial palisade structure; these features suggest that the stromatolites were largely phototrophic in origin. The deep iron-rich weathering profile of the Dresser stromatolites makes them pertinent analogues for potential microbialites in altered carbonates on Mars. Were putative biogenic meso- and micromorphologies identified in habitable Martian settings by rover imaging systems, such materials would be compelling targets for sample return