West-to-east profile of the Florida-Bahamas carbonate platform.
Deep in the Gulf of Mexico, along the edge of the great carbonate platform that breaks the surface as Florida and the Bahamas, thrives a diverse community of animals that does not depend upon the sun for energy. Instead, they feast on carbohydrates provided by symbiotic bacteria. Since there are no ocean-floor vents spewing mutrients and hot water in the area, scientists have wondered where these bacteria obtain the methane and sulfides that nourish them. C.S. Martens and C.K. Paull, of the University of North Carolina, propose that bacteria living miles down within the carbonate platform generate the methane and sulfides as they consume organic matter buried long ago in the limestone. These excreted, energy rich gases and fluids seep upward and outward, sustaining biological communities along the edge of the platform.
(Monastersky, R.; "Buried Rock, Bacteria Yield Deep-Sea Feast," Science News, 140:103, 1991.)
Comment. (1) Looking far back in time, the sun was, of course, the energy source, because it helped create the buried organic matter. (2) However, there is always the possibility that the methane seeping out of the earth is abiogenic. See BLACK GOLD -- AGAIN under Geology. (3) How deeply into the crust has life penetrated? The Soviets reported bacteria at 12 kilometers in their drill hole on the Kola Peninsula.