Life uncovered by the deepest-ever marine drilling expedition has been analysed by scientists.
The International Ocean Discovery Program (IODP) found microbes living 2,400m beneath the seabed off Japan.
The tiny, single-celled organisms survive in this harsh environment on a low-calorie diet of hydrocarbon compounds and have a very slow metabolism.
The findings are being presented at the America Geophysical Union Fall Meeting.
Elizabeth Trembath-Reichert, from the California Institute of Technology, who is part of the team that carried out the research, said: “We keep looking for life, and we keep finding it, and it keeps surprising us as to what it appears to be capable of.”
The IODP Expedition 337 took place in 2012 off the coast of Japan’s Shimokita Peninsula in the northwestern Pacific.
From the Chikyu ship, a monster drill was set down more than 1,000m (3,000ft) beneath the waves, where it penetrated a record-breaking 2,446m (8,024ft) of rock under the seafloor.
Samples were taken from the ancient coal bed system that lies at this depth, and were returned to the ship for analysis.
The team found that microbes, despite having no light, no oxygen, barely any water and very limited nutrients, thrived in the cores.
To find out more about how this life from the “deep biosphere” survives, the researchers set up a series of experiments in which they fed the little, spherical organisms different compounds.
Dr Trembath-Reichert said: “We chose these coal beds because we knew there was carbona, and we knew that this carbon was about as tasty to eat, when it comes to coal, as you could get for microbes.
“The thought was that while there are some microbes that can eat compounds in coal directly, there may be smaller organic compounds – methane and other types of hydrocarbons – sourced from the coal that the microbes could eat as well.”
The experiments revealed that the microbes were indeed dining on these methyl compounds.
The tests also showed that the organisms lived life in the slow lane, with an extremely sluggish metabolism.
They seem to use as little energy as possible to get by.