Microbial endoliths are known from intertidal and shallow water marine environments with only a few reports on their occurrence in greater oceanic depths. We find microbial endoliths and microborings in abundance down to depths of over 4,000 m (13,000 ft), which means that a significant portion of the ocean floor is the site of microbial endolithic activity. Microbial endoliths are a strictly benthic phenomenon, and no endolith activity takes place in the water column. Endoliths leave a specific and well-preservable overprint on the sedimentary record of the oceans. The taxonomic composition of endolith assemblages reflects their environmental requirements and is depth related. The extent of endolith activity is a function of their exposure time at the sediment-water inte face, which in turn is a function of sedimentation rate. Thus, the endolithic signature in the sedimentary record contains information on the conditions at the site and time of sediment formation.

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