Nanophase Goethite as a Promising Target in the Search for Past Life on Mars.

The ubiquitous iron oxides and oxyhydroxides on Mars represent intriguing targets in the search for evidence of past microbial life on the Red Planet. So far, no studies have systematically investigated microbial fossils in fluviolacustrine ferricrete composed entirely of nanophase goethite; thus, our understanding of biosignatures in such deposits is limited. Here, we report exceptionally well-preserved microfossils in laminated nanophase goethite from the Miocene McGraths Flat Lagerstätte, New South Wales, Australia. Using scanning electron microscopy and energy dispersive spectroscopy, we identified a diverse range of fossil morphotypes, including bacteria and fungi. Syngenetic forms embedded in the sedimentary matrix and post-depositional endolithic colonizers were recognized. Our findings establish nanophase goethite as an excellent preservation medium for microfossils, capable of preserving subcellular details across multiple generations of microbial communities, and highlight nanophase goethite as a promising target for future Mars exploration missions.