It has been only a few decades since scientists have discovered that life at the surface of our planet and in oceans is just a fraction of the global biomass. Indeed, a large portion of life on Earth could occur beneath the oceans’ abyss, within marine sediments. In these ‘extreme’ environments, there is no sunlight, nor oxygen, and pressures are extremely high. Yet, it is the habitat of unicellular organisms, the simplest of all life forms, which can survive by ‘breathing’ chemicals carried by the interstitial fluids, fossil organic matter, hydrogen and methane.
Our present understanding of deep microbial life, its extent and relationships/interactions with the subsea floor largely derive by deep-sea drilling science programs (e.g. IODP) that allow directly sampling and studying these buried environments. Deep subsea floor life has been also documented at the ocean bottom in deep hypersaline anoxic basins and mud volcanoes, which, unlike traditional volcanoes, are driven by chemistry and not heath.
