Recent discoveries have raised the possibility of a huge and diverse subsurface biosphere of microbial life. Below the ocean floor, a variety of chemical reactions between seawater and rocks, taking place over a range of temperatures, creates a chemical bouillabaisse. These chemicals diffuse upward and become sources of energy and carbon that sustain a wide variety of microbes. The microbes have evolved to take advantage of specific conditions in particular niches.
* White numbered dots: Microbes living in the subsurface at or near deep-sea hydrothermal vent sites exploit a wide range of conditions. Here is a list of known or possible chemical reactions microbes use to live and grow. (Illustration by Jayne Doucette, Woods Hole Oceanographic Institution)