Our study has confirmed that there's no place in the oceans that doesn't have these features

Dr Hubert Staudigel

Analysing rock samples from under the Atlantic and the Pacific, scientists have seen evidence that microscopic organisms are eating into volcanic rock, leaving worm-like tracks.

The microbes alter the chemistry of the rock, allowing it to exchange chemicals and minerals with seawater when they come into contact.

The process influences global chemical interactions, such as the carbon cycle which plays a crucial role in the Earth's climate.

'Rock bottom'

"These organisms are the bottom of the food chain," according to Dr Hubert Staudigel, of the Scripps Institution of Oceanography, at the University of California, US.

The traces they left behind were seen in samples of volcanic rock recovered from beneath the sea floors of the Atlantic and the Pacific by the Ocean Drilling Program (ODP).

The scientists have found the tracks everywhere they have looked for them

Samples were extracted from as deep as six kilometres (four miles) below sea level, sliced into sections and examined through a scanning electron microscope.

"We've documented how extensive these microscopic organisms are eating into volcanic rock, leaving worm-like tracks that look like someone has drilled their way in," says Dr Staudigel.

It appears to be a common process throughout the ocean. "Our study has confirmed that there's no place in the oceans that doesn't have these features," he adds.

Prior to this analysis, most scientists believed that the process of volcanic rock changing from one state to another was a purely chemical-physical process. Now, it seems biology is involved.

If true, the tiny microbes have an importance out of all proportion to their size.

Deep biosphere

Some scientists believe that most of the life on Earth, in terms of the quantity of organic matter, may not live on the surface of our world, but be in the form of microbes in rock in the Earth's crust. Certainly, the discovery and exploration of the "deep biosphere" has been one of the highlights of science in the past decade.

Presently, no one knows how deep this biosphere goes, but there are some hints in the new data.

The number of the worm-like tracks in the rocks diminishes with depth; at 300 metres (985 feet) below the sea floor, they become much rarer.

Although it is difficult to draw conclusions from samples returned from only a few sites, Dr Staudigel believes his team has determined the depth of the biosphere.

He says the microbes may tunnel their way into the rock to derive chemical energy from the minerals, and to find protection from larger grazing organisms. If so, they may be the "rock bottom" of the food chain, living off rock.

The material released may interact with the ocean and be a key feature in global cycles such as the movement of carbon through living and non-living things.

It is even suspected that such microbes, if they arose early in Earth's history, could have altered the global conditions of a primitive Earth to make possible the development of more advanced organisms.

The research is published in Geochemistry, Geophysics, Geosystems, an online journal.