March 15, 2013
First Evidence Of Life Deep Under Oceanic Crust Realized
Lee Rannals for redOrbit.com — Your Universe Online
Scientists writing in the journal Science say they have found the first direct evidence of life in the deeply buried oceanic crust.
Researchers on board the Integrated Ocean Drilling Program's (IODP) research vessel JOIDES Resolution drilled a water depth of 1.5 miles and hundreds of feet of sediment into the oceanic crust off the west coast of North America. After examining rock samples from this depth, they were able to uncover evidence of life, suggesting this ecosystem is largely supported by chemosynthesis, which is the biological conversion of molecules using oxidation or methane as a source of energy, rather than sunlight like in photosynthesis.
Dr Mark Lever, a scientist at the Center for Geomicrobiology at Aarhus University, Denmark, said they learned that sunlight is a prerequisite for life on Earth. In the photosynthesis process, organisms use sunlight to convert carbon dioxide into organic material. However, life in the rock material in the oceanic crust is fundamentally different.
"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.
Ocean crust covers about 60 percent of the Earth's surface, making it the largest ecosystem on the planet. Since the 1970s, scientists found local ecosystems, like hot springs, are sustained by chemical energy.
"The hot springs are mainly found along the edges of the continental plates, where the newly formed oceanic crust meets seawater. However, the bulk of oceanic crust is deeply buried under layers of mud and hundreds to thousands of kilometers away from the geologically active areas on the edges of continental plates. Until now, we've had no proof that there is life down there," says Dr Lever.
Although the ecosystem is mostly based on hydrogen, several different forms of life are found in these depths. The hydrogen-oxidizing microorganisms create organic material, forming the basis for other microorganisms in the basalt. Some of the organisms get their energy by producing methane or reducing sulphate.
"We collected rock samples [34 miles] from the nearest outcrop where seawater is entering the basalt. Here the water in the basaltic veins has a chemical composition that differs fundamentally from seawater, for instance, it is devoid of oxygen produced by photosynthesis. The microorganisms we found are native to basalt," explains Dr Lever.
Laboratory cultures in the study have shown that the DNA belonging to these organisms is not fossil.
"It all began when I extracted DNA from the rock samples we had brought up. To my great surprise, I identified genes that are found in methane-producing microorganisms. We subsequently analyzed the chemical signatures in the rock material, and our work with carbon isotopes provided clear evidence that the organic material did not derive from dead plankton introduced by seawater, but was formed within the oceanic crust," Lever said.
He added that sulphur isotopes showed the team that microbial cycling of sulphur had taken place in the same rocks.
"These could all have been fossil signatures of life, but we cultured microorganisms from basalt rocks in the laboratory and were able to measure microbial methane production," says Lever.
Finding life in these harsh environments on Earth could shed light on what kinds of life lives on other planets. Researchers studying microorganisms in Antarctica are finding better examples of what life on Mars and other extreme environments may be like.
Scientists from the University of Maryland reported in the journal BMC Biotechnology recently about how they found new aspects of certain proteins that could enable life to function on Mars. They found significant differences in the core proteins of Antarctic extremeophile bacteria, or Haloarchaea, compared to similar proteins in other microorganisms. These differences allow the extremeophiles to tolerate severe living conditions.