Scientists have found an unexpectedly abundant amount of bacterial life more than 4,600 feet (1,400 meters) below the seabed, a discovery that has ramifications for the search for life on Mars and strategies for adapting to climate change on Earth.

Writing in the open-access, online journal PLoS One, Olivia Mason of Oregon State University and colleagues point out that although the geology of oceanic crust has been extensively studied, its biology has not—partly because digging to such depths poses logistical and financial challenges and partly because expectations of finding rich biological life in the crust have been limited.

In most areas, the deepest layer of ocean crust, known as the gabbro layer, doesn't even begin until the crust is about two-miles (3,200-meters) thick. But at a site in the Atlantic Ocean near an undersea mountain, the Atlantis Massif, gabbro rock formations are closer to the surface than usual because they have been uplifted and exposed by faulting. Mason and colleagues took advantage of this feature to drill into comparatively shallow depths and study the microbiology of the crust.

Perhaps not surprisingly given the depth and extreme conditions, although the researchers found microbial life, it was not at high density. The microbes that were there, however, showed some interesting adaptations to life in those extreme conditions. Some were degrading hydrocarbons, some appeared to be capable of oxidizing methane, and others contained genes for fixing, or converting from a gas, both nitrogen and carbon. Interestingly, analysis of the hydrocarbons suggests that they originate from deep within the crust, suggesting that the microbial ecosystem is operating entirely independently of the surface biosphere.

The findings are also of interest because little is known about the role the deep ocean crust may play in carbon storage and fixation. Increasing levels of carbon dioxide, a greenhouse gas when in the atmosphere, in turn raises the levels of carbon dioxide in the ocean.

But if these microbes are indeed able to fix carbon, the researchers say their findings may lend credence to one concept for reducing carbon emissions in the atmosphere, by pumping carbon dioxide into deep subsurface layers where it might be sequestered permanently.

The researchers also noted that methane found on Mars could be derived from geological sources, and concluded that subsurface environments on Mars where methane is produced could support bacteria like those found in this study.

“These findings don't offer any easy or simple solutions to some of the environmental issues that are of interest to us on Earth, such as greenhouse warming or oil spill pollution,” said Martin Fisk of Oregon State University in a press release to announce the findings. “However, they do indicate there's a whole world of biological activity deep beneath the ocean that we don't know much about, and we need to study.” 

Source: Mason, O.U. et al. 2010. First investigation of the microbiology of the deepest layer of ocean crust. PLoS One5(11): e15399. doi:10.1371/journal.pone.0015399

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