Stromatolite reef from the Early Archaean era of Australia

The 3,430-million-year-old Strelley Pool Chert (SPC) (Pilbara Craton, Australia) is a sedimentary rock formation containing laminated structures of probable biological origin (stromatolites). Determining the biogenicity of such ancient fossils is the subject of ongoing debate. However, many obstacles to interpretation of the fossils are overcome in the SPC because of the broad extent, excellent preservation and morphological variety of its stromatolitic outcrops—which provide comprehensive palaeontological information on a scale exceeding other rocks of such age. Here we present a multi-kilometre-scale palaeontological and palaeoenvironmental study of the SPC, in which we identify seven stromatolite morphotypes—many previously undiscovered—in different parts of a peritidal carbonate platform. We undertake the first morphotype-specific analysis of the structures within their palaeoenvironment and refute contemporary abiogenic hypotheses for their formation. Finally, we argue that the diversity, complexity and environmental associations of the stromatolites describe patterns that—in similar settings throughout Earth's history—reflect the presence of organisms. Biodiversity rocks The existence — or otherwise — of life on Earth in the Archaean eon (prior to 2,500 million years ago) has been a matter of heated debate. Much of this centres on whether layered sedimentary structures called stromatolites reflect the activities of colonial microorganisms, as is the case today, or betray some non-biological process. The case for life is boosted by a new analysis of a remarkable 10-km-long rocky outcrop in Western Australia. The stromatolites here are around 3,430 million years old, and display characteristics similar to those found in younger microbial reefs: this is not a series of isolated fossils — more like an entire ecosystem in fossil form. Life not only existed way back then, it seems, but it was thriving. The cover image shows a conical stromatolite from the reef outcrop: no scale bar, but the shades peering from beneath the Nature logo indicate size.