Large domal stromatolites in the Paleoarchean ocean at 3.47 Ga

Abstract Stromatolites are indicators of life on Earth since at least 3.5 Ga and possibly 3.7 Ga. From the mid-Archean onward, records of stromatolites display a range of morphologies and sizes, indicating that microorganisms were present in a variety of habitats. By comparison, the existing Paleoarchean stromatolite record is limited to small decimeter-scale domes, cones, and tufts that occur in evaporitic environments. Here, we document large domal stromatolites with ~1.5 m width and 0.8 m height from a chert-jasper-carbonate member in the Paleoarchean (ca. 3.47 Ga) Mount Ada Basalt, Pilbara craton, Western Australia. Sedimentological features and trace-element chemistry show that the stromatolites grew on seafloor pillow basalts in an anoxic environment with hydrothermal influence. Aqueous alteration of basaltic-komatiitic crust likely supplied key nutrients, extending benthic microbial habitats into the deeper Paleoarchean ocean and supporting a thriving biosphere independent of continental exposure.