FTIR raw data of organic molecules in basalt samples from IODP Hole 336-U1383C and 330-U1376A

The organic matter associated with those textures shows evidence for the occurrence of remnants of complex biomolecules like proteins. The biosignatures from the older Louisville Seamount Trail (~70 Ma), for which archaeal origin is suggested, are much more texturally diverse and the associated organic molecules are also more degraded. We hypothesize that microbial communities change significantly during crustal evolution and aging, and suggest that microbes that are associated with older and severely altered crust are not responsible for the biotic alteration textures commonly found in subseafloor basalt glass.

We suggest that biotic alteration textures are related to microbially-catalyzed oxidation of Fe2+, Mn2+, and S compounds and form predominantly within the first ~10 Ma of crustal evolution. In older crust with less glass and decreased permeability, other metabolic pathways may dominate which only leave molecular biosignatures. We propose that diverse biosignatures in oceanic crust may form during different stages of crustal evolution.