In some regions, huge amounts of sediments pile atop the seafloor near hydrothermal vents. Organic matter in the sediments is subjected to heat and pressure, producing hydrocarbons (including oil) that microbes use to live and grow.
* 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)