Micrograph of showing sulfur-rich particles formed by microbial activity
Courtesy of NOAA
Life on the surface depends on a process called photosynthesis. Photosynthesis occurs in green plants when they use the sun’s energy to produce simple sugars from carbon dioxide and water. Photosynthetic organisms exist in the ocean as well but near the surface in what is known as the photic zone(upper layer of the ocean surface which transmits enough light for photosynthesis to occur). Photosynthetic organism are found at the bottom of the food chain and are eaten by other organisms to produce who digest them to produce energy.
At the bottom of the ocean no light exists so using photosynthesis as a source of energy for life is not an option. Black Smokers emit a variety of chemical compounds such as hydrogen sulphide and methane that are oxidized when they come in contact with the sea water. This chemical reaction produces energy which is harnessed by chemoautotrophs to produce simple biological compounds. The chemosynthetic microbes are either eaten by other organism or in some cases live in a symbiotic relationship with a host organism.
Sources: BRIDGE, NOAA