A new paper describes the finding of live microbial communities in the earth’s crust deep below the seabed. Without recourse to sunlight and photosynthesis these bacteria seem to have found a different source of energy. “The bacteria feed on chemicals that are released when water seeps down through the rocks. The rocks contain iron ions that can react with sea water and produce hydrogen, which the bacteria can use as an energy source for producing their own organic matter,” says author Mark Lever. “This form of chemical synthesis, which is an alternative energy source to photosynthesis, also occurs elsewhere on Earth, for instance around warm springs in the seabed. But this is the first time that it has been found in the earth’s crust below the sea.”
M.A. Lever et al., “Evidence for microbial carbon and sulfur cycling in deeply buried ridge flank basalt,” Science, 339:1305-08, 2013. DOI:10.1126/science.1229240
The Scientist: Tiny fissures in 3.5-million-year-old rock hundreds of meters below the seabed are home to microbes that gain their energy from the rock itself, according to a paper published in Science today (March 14). The study suggests that the largest ecosystem on the planet depends on energy, not from the sun, but from chemical reactions.
“The fact that you can get viable microbes out of those rock samples—and they’re clearly indigenous; they’re not contaminants—that’s just tremendously exciting,” said Andy Fisher, a professor of earth and planetary sciences at the University of California, Santa Cruz, who was the lead scientist on the drilling vessel.
The oceanic crust of volcanic-derived basalt rock lies below the sedimentary seabed, covers approximately two thirds of the Earth’s surface, and is on average 7 kilometers thick. Although scientists have found evidence of life within this vast expanse of rock, the samples obtained were of crustal fluids, rather than the basalt itself, explained Mark Lever, an ecologist at Aarhus University in Denmark, who led the study. “Ours was the first direct study that conclusively showed that there is life within these rocks,” he said. …..
….. The thick layer of sediment “acts like a blanket” to keep the relatively young crust warm, around 64°C, explained Damon Teagle, a professor of geochemistry at Southampton University in the UK, who was not part of the team. It also largely prevents seawater from entering the rock from above, he said. There is, however, horizontal flow of water through the rock from distant sediment-free entry points created by small seamounts. But, by the time that water has reached the site where Lever’s rock samples were collected, “it’s suggested to be over 10,000 years old,” said Lever. The water in the samples is also free of oxygen and chemically quite distinct from seawater due to the filtering effect of passing through rock. …..
…… Back in his land-based lab, Lever and colleagues extracted DNA from the fissure samples and identified genes for methane and sulfur metabolism, consistent with microbes living in an oxygen-free environment. He also observed that the chemical composition of the rock samples was in line with methane and sulfur metabolism by resident microbes.
The presence of microbial genes and characteristic rock chemistry was not sufficient to confirm the existence of life, however. “The sulfur and carbon isotopes that were analyzed could, in theory, have been produced thousands or millions of years ago,” said Lever, and the microbial DNA could have been from fossils. But, he added, “we didn’t just find DNA.”
The team also found that rocks incubated for several years under conditions resembling the crustal environment exhibited rising methane levels. “[It’s] evidence that [the microbes] are active and directly gaining energy from reactions with the rocks,” Lever said. ….
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