Volcanic rocks of the oceanic crust as habitat for recent to Paleoarchean microbial life: A review

Abstract

Submarine alteration of basaltic glass in pillow lavas and hyaloclastites result in 1) abiotic palagonite with smooth interface between the fresh and altered glass, and 2) biogenically-produced irregular granular and tubular textures. In the upper oceanic crust, the bio-generated textures are dominant, but become progressively less abundant downwards into the volcanic pile to finally disappear at ca. 500 m depth, contemporaneously with the increase in palagonite alteration. The bio-related granular and tubular alteration structures can be found in originally basaltic glass of pillow lavas dating back to ca. 3.5 Ga, providing information of the earliest life on Earth. Element mapping of these bio-related textures show traces of carbon even in the oldest examples. Further, carbon isotope data of the glassy pillow rims and crystalline material exhibit significantly lower δ¹³C_carbonate of the former than the latter. Thus, both the carbon signatures and the C-isotope signatures are consistent with microbial influence during alteration of the basalt glass.