"These are probably not only the deepest, but the hottest organisms found in deep marine sediments," said R. John Parkes, a geobiologist at Cardiff University in Wales. "I was hoping we would find them this deep, so we were very excited that we actually did confirm they were present. It's fascinating to know what proportion of our planet actually has living organisms in it."
While life has been known to exist at even greater depths beneath land — such as bacteria found nearly two miles underground in a gold mine in South Africa — life under the sea had previously only been detected to depths of about half a mile (842 meters) below the seafloor.
Parkes and his colleagues analyzed core samples returned from the Ocean Drilling Program. They found evidence for prokaryotic cells, which lack a central nucleus, that appear to be from the archaea family, a sister domain to bacteria.
The newly-discovered life likely gets its energy from methane. It thrives in 111 million–year-old rocks, enduring temperatures between 140 to 212 degrees Fahrenheit (60 to 100 degrees Celsius). In this extreme environment, life is relatively sparse.
"There's no light around, there's no oxygen around," Parkes told LiveScience. "It's basically just rocks, but there is still some space for water, which the organisms need."
This discovery of living creatures in some of Earth's most extreme hideouts may shed light on the search for extraterrestrial life.
"Until we know what's there on Earth, we're not going to have a clue what's possible on other planets," Parkes said. "I think people have taken the message from this type of work that it's no longer sufficient to take a scoop of Martian soil from the surface and say there's no life. If life on Earth can go as deep as several kilometers, there's no reason why that wouldn't be true under similar conditions on another planet."
The team detailed their findings in the May 23 issue of the journal Science.
Source: Live Science