Although Darwin predicted life in the continental deep subsurface almost two hundred years ago only recently we started to pay attention to this new geomicrobiological frontier, consequence of the skeptic opinion on its existence and considering preliminary data consequence of contamination during the inevitable drilling processes. Although most of the diversity information has been obtained from artesian well groundwater, with its limitations to understand the operation of the underground biogeochemical cycles, today there is sufficient information from devoted continental hard rock drillings to evaluate that an important part of the prokaryotic biomass and diversity resides in the so call dark biosphere. During the development of the Iberian Pyrite Belt Subsurface Life Detection (IPBSL) drilling project we collected sufficient information along a 613 m borehole, using diverse methodologies, to describe the coupled operation of the most important biogeochemical cycles (C, H, N, S and Fe) in the oligotrophic deep subsurface of the Iberian Pyrite Belt in the absence of radiation. These results underline the need to amplify the extremely restrictive definition of Habitable Zone (HZ) considering the possibility of life in the subsurface and that most of the detected rocky exoplanets cannot hold water in their surface.