London, May 23 : Scientists have found microbes in a 111-million-year-old rock buried 1.6 kilometres below the sea floor, a discovery that marks the deepest living cells ever to be found beneath the sea floor.
According to a report in Nature News, this finding beats the old record of the presence of microbial life - 842 metres below the sea floor.
Microbes have been found in nearly every nook and cranny that Earth has to offer, from deep-sea vents to the drainage from acid mines.
Some estimates reckon that two-thirds of Earth's microbial biomass could be found below the sea floor - although given the difficulty of sampling so far below the waves, it is almost impossible to say for certain.
But conditions become progressively harsher deeper in the sediment. The rock becomes older and more likely to be depleted of the organic material for microbes to feast on.
Meanwhile, pressure and temperature steadily rise. In some regions, the temperature rises 20 degree C for every kilometre deeper below the sea floor.
At present, the uppermost temperature at which life can survive is estimated at around 120 degree C.
"If temperature is the ultimate limit, then one might reasonably expect the biosphere to extend as much as 5 kilometres below the sea floor," said Steven D'Hondt, an oceanographer at the University of Rhode Island.
The new sample was retrieved from the Newfoundland Margin in the Atlantic Ocean, by the ocean drilling ship JOIDES Resolution.
John Parkes, a geobiologist at the University of Cardiff, UK, and his colleagues, extracted the microbes from the inner core of the sediment samples, where they were unlikely to have been contaminated with external seawater. hey found simple organisms known as prokaryotes in every sample.
Prokaryotes are organisms that often have just one cell. Their peculiarity is that, unlike any other form of life, their DNA is not neatly packed into a nucleus.
About 60% of the cells Parkes and his team found were alive. They are related to organisms found in deep-sea hydrothermal vents.
The researchers were also able to isolate DNA from the microbes.
DNA sequences indicated that several species of Archaea, mainly members of the heat-loving genus Pyrococcus, lived 1,000 metres deep. As depth and methane concentrations increased, they found additional DNA sequences from microbes that oxidize methane to produce energy.
According to Parkes, his team's discovery might one day help find life on other planets.