One of science's simple but elegant observation -- all life gets its energy, ultimately, from the sun -- has been proven wrong.
Doubts about it arose in 1977 when marine biologists discovered luxuriant animal communities thriving on the ocean floor about 8,000 feet below the surface in total darkness. Unlike the well-known deep-sea animals that live on organic matter falling from the surface, the newly found animals were clustered around underwater vents that spewed hot, mineral-rich water.
These hydrothermal vents, found first near the Galapagos Islands off Ecuador, appear to support compact ecosystems comprising colorfully fringed worms, mussels, clams and crabs. They constitute a food chain that derives its energy from something near the vents.
Biologists found that water near the vents contains unusual forms of bacteria that feed upon chemicals exuded by the vents, mainly compounds of sulfur and oxygen called sulfides. The bacteria employ a metabolic process that breaks apart the sulfur and oxygen atoms, extracting the energy that bound them. The process is fundamentally different from that of conventional bacteria.
Early in the research, it appeared that the unusual bacteria were the primary food of the worms, which are eaten by the higher animals. Still, it was not certain that the animal community relied exclusively on the sulfide-eating bacteria.
This reliance now has been established by scientists from the University of California at Santa Barbara. Using a small research submarine equipped with a newly developed instrument for measuring water chemistry at the site, Kenneth S. Johnson has obtained evidence that the amount of sulfide energy being removed from the water correlates with the abundance of life near the vents.
Similar forms of chemically powered bacteria, believed to be close relatives of the earliest forms of life on Earth, have since been found in sewage outfalls of Los Angeles, in natural gas seeps in the Gulf of Mexico and other hydrothermal vents.
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