OCEANIC PILLOW LAVAS AS A HABITAT FOR MICROBIAL LIFE THROUGH TIME

The upper oceanic crust consists predominantly of pillow lavas that, soon after their eruption, are colonized by microbes when the ambient temperature ameliorates. During the process of microbial interaction with the glassy rims of pillows (termed “bioalteration”) several types of bio-traces (micro-textures, geochemical and isotopic) are generated, of which micro-textures are the most spectacular. Bioalteration features are abundant in the upper 300 m of the in situ oceanic crust, and have been found in Phanerozoic and Proterozoic ophiolites and greenstone belts back to 3.5 Ga. The bioalteration features are most useful for mapping the depth of the oceanic biosphere, giving indications of the tectonic control of the alteration processes, and in the search for the earliest life on the Earth. Systematic interdisciplinary studies of the bioalteration of modern and ancient oceanic crust reveal significant new information on how biological activities influence seafloor weathering fluxes and the important role submarine volcanoes have played in the biological evolution of the Earth.