It’s known as the deep biosphere, or the dark energy biosphere. What is it? Microbes - bacteria, archaea, even fungi - living not at the bottom of the ocean, but in the bottom of the ocean. We aren't just talking about the ocean version of soil bacteria, living in the seafloor mud (although that is part of the story). No, we're talking about microbes living in cracks in the rocks deep below that mud, in the most extreme case to date, a mile and a half below the seafloor.