Mark Lever, Aarhus University, works under sterile conditions in the laboratory. Familiar tools such as a hammer are necessary for a geomicrobiologist working with rock samples from the oceanic crust. (Credit: Photo: Jesper Rais, AU Communication.)

Mar. 14, 2013 — The core drill slides through a drill pipe, extending from the drill ship at the sea surface, through a water depth of 2.5 km and hundreds of metres of sediment, into the oceanic crust off the west coast of North America. Microbiologist Mark Lever is on board the Integrated Ocean Drilling Program's research vessel JOIDES Resolution to examine rock samples from the depths.

The results of the studies he and his colleagues carried out are published today in the journal Science.

"We're providing the first direct evidence of life in the deeply buried oceanic crust. Our findings suggest that this spatially vast ecosystem is largely supported by chemosynthesis," says Dr Lever, at the time a PhD student at the University of North Carolina at Chapel Hill, USA, and now a scientist at the Center for Geomicrobiology at Aarhus University, Denmark.

Energy from reduced iron

We have learned that sunlight is a prerequisite for life on Earth. Photosynthetic organisms use sunlight to convert carbon dioxide into organic material that makes up the foundation of Earth's food chains. Life in the porous rock material in the oceanic crust is fundamentally different. Energy — and therefore life's driving force — derives from geochemical processes.

"There are small veins in the basaltic oceanic crust and water runs through them. The water probably reacts with reduced iron compounds, such as olivine, in the basalt and releases hydrogen. Microorganisms use the hydrogen as a source of energy to convert carbon dioxide into organic material," explains Dr Lever. "So far, evidence for life deep within oceanic crust was based on chemical and textural signatures in rocks, but direct proof was lacking," adds Dr Olivier Rouxel of the French IFREMER institute.

Our biosphere is extended

The oceanic crust covers 60 per cent of Earth's surface. Taking the volume into consideration, this makes it the largest ecosystem on Earth. Since the 1970s, researchers have found local ecosystems, such as hot springs, which are sustained by chemical energy.

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