Type of isopod, which lives at the bottom of the sea. Photo courtesy of

In 1977 a second type of primary productivity was discovered. It was then that other remarkable forms of life, chemosynthetic animals, were unexpectedly discovered on dives of the deep submergence vehicle (DSV) Alvin in the Pacific Ocean. This discovery shook the foundations of marine biology. It was called by some, the most important biological discovery of the 20th century. Some of the animals didn't even have a mouth or gut! And in 1984 it was found that these same kinds of animals were living in the Gulf of Mexico too.

Photosynthetic production was replaced by chemosynthesis. Here is the equation for chemosynthesis: 6CO2 + 6H2O + 3H2S —› C6H12O6 + 3H2SO4. You will notice it is very similar to the equation for photosynthesis. Chemosynthesis uses carbon dioxide and water, just like photosynthesis, but instead of using sunlight chemosynthesis relies on sulfur chemicals for energy. Chemosynthesis also produces glucose just like photosynthesis, but rather than creating oxygen as a byproduct, it creates sulfur compounds.

Chemosynthetic animals were found to be able to extract their needs from dissolved gasses in their environment in the presence of dissolved oxygen. These first chemosynthetic animals, huge tube worms (known as vestimentiferans) and clams, were discovered living near hydrothermal (hot-water) vents in the spreading seafloor at the mid-ocean ridge. These remarkable animals were obtaining their energy from dissolved hydrogen sulfide issuing from the vents. To accomplish this process the animals held certain bacteria within their tissues in a mutually-beneficial ("symbiotic") relationship. Today, similar chemosynthetic animal communities have been discovered in many locally-unusual habitats all around the world where the necessary gasses vent or seep from the ocean floor. In the Gulf there are "cold seeps" at the bottom that variously release hydrocarbons (mostly methane) or hydrogen sulfide depending on the local geology. But the chemistry of both seeps and vents would be considered inhospitably toxic for many "conventional" forms of life.

and Teachers' Domain, Deep-Sea Vents and Life's Origins, published December 17, 2005, retrieved on July 15, 2010,
Last modified: Wednesday, 19 October 2011, 8:46 AM