Terrestrial and marine habitats have been considered the ecosystems with the highest primary production on Earth by far. Microscopic algae in the upper layers of the oceans and plants on land bind atmospheric carbon (CO2) and produce plant material driven by photosynthesis. Since sunlight does not penetrate into the subsurface, hardly any such primary production is to be expected.
Click here for original story, Life in the Earth’s interior is as productive as in some ocean waters
Source: Phys.org