News in Science

Life discovered deep under ocean crust

Strange microbes The first direct evidence of communities of micro-organisms buried deep in the oceanic crust has been discovered during deep sea drilling off the United States Pacific coast.

Research reported in the journal Science, indicates these micro-organisms rely on chemical reactions - not sunlight or photosynthesis - to produce energy.

The study's findings not only help scientists understand more about the vast ocean crust ecosystem, which covers 60 per cent of the Earth, but have implications for discovering life on other planets such as Mars.

The idea that organisms could survive on chemical energy - a process known as chemosynthesis - has been known since 1880, and more recently seen in ecosystems clustered around hydrothermal vents along the mid-ocean ridges where new crust forms.

But the bulk of the ocean's crust is deeply buried under layers of mud and thousands of kilometres away from the edges of the continental plates, says Dr Mark Lever, at the time a PhD student at the University of North Carolina, and now a scientist at Aarhus University.

"Until now, we had no proof that there is life down there," says Lever.

Lever and colleagues drilled 600 metres into seafloor sediment and underlying basaltic oceanic crust, 2.5 kilometres below the surface.

They specifically selected a location 55 kilometres from the nearest outcrop where seawater could enter the basalt crust, ensuring any micro-organisms found, were native to the basalt, rather than being transported through seawater.

"Here the water in the basaltic fissures and cracks has a chemical composition that differs fundamentally from seawater ... [and is] devoid of oxygen produced by photosynthesis," says Lever.

Using special equipment to prevent external micro-organism or seawater contamination during drilling and transport, the researchers extracted uncontaminated rock from inside the sample.

They successfully grew microbes by incubating the samples in conditions mimicking their native habitat.

The samples were kept at temperature of 65°C for several years in an environment designed to resemble the chemistry of water flowing through fissures and cracks in oceanic crust.

"What we found came as a huge surprise," says study co-author Dr Andreas Teske of the University of North Carolina.

The energy sources keeping these microbes alive comes from chemical reactions between water flowing through the basalt and reduced iron compounds, such as olivine, releasing hydrogen, says Teske.

"The microbes use this hydrogen to convert carbon dioxide into methane.

"These create organic material forming the basis for other micro-organisms in the basalt, which get their energy by reducing sulphate, or breaking down organic carbon through fermentation," says Teske.

Now that microbes have been found deep in the basalt crust, Teske says the next step is to find out what happens thousands of kilometres away from any active mid-ocean ridges or subduction zones.

"That could harbour a different kind of life," he says.

The Red Planet

Teske says the findings indicate it could be possible to find life based on chemosynthesis on other planets.

"This brings up a completely new dimension of where life can hide, so astrobiologists would be interested," he says.

"I would bet drilling 500 or 1000 metres below the Martian surface would stand a reasonable chance of finding life on Mars.

"It would have had to move underground, the surface is cold, dry and exposed to radiation.

"But the sub-surface, who knows? Martian microbes could have survived there ever since the planet lost its atmosphere four billion years ago," says Teske.