The scientific ocean drilling community has been retrieving cores from hundreds of meters below the seafloor since the inception of the Deep Sea Drilling Project (DSDP) in 1968. While microbiological research was not part of the scientific impetus for the creation of DSDP, it became apparent to geochemists that some of the observations in pore water chemistry indicated microbiological activity at great depth (e.g., Claypool and Kaplan, 1974). Site after site yielded profiles of microbiologically relevant compounds (e.g., sulfate, methane) that indicated microbial activity.

Smith, D.C., and S. D’Hondt. 2006. Exploration of life in deep subseafloor sediments. Oceanography 19(4):58–70, https://doi.org/10.5670/oceanog.2006.05.

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