SYDNEY: Life can exist deep underground for millions of years without any energy input from the sun, according to a new international study.
A community of bacteria that obtains its energy not from sunlight, but from radioactive decay, has been located three kilometres underground in a gold mine in South Africa. The team of scientists, led by Princeton University’s Tullis Onstott, say that this subterranean ecosystem is the first example of a stable community that receives no energy from the sun.
“The bottom line is: water plus rocks plus radiation is enough to sustain life for millennia,” Onstott told the Washington Post.
Scientists have long known of the existence of microbes living far underground, cut off from sources of sunlight-based energy. According to the report, which appeared last week in the journal Science, until now no one knew whether these communities were stable.
The knowledge that life can exist for indefinite periods totally without energy input sunlight is very exciting for scientists, because it strengthens the chances of finding life on other planets, like Mars.
“This is a very nice potential model of the habitability of Mars, Jupiter’s Europa and other moons,” said one of the paper’s authors, Steven D’Hondt of the University of Rhode Island, in an interview with the Post.
According to the authors, the surfaces of Mars, Europa, and other planets are quite inhospitable to life, either because of extreme temperatures or lack of water. Scientists think that they might find more suitable environments below the surface, though. Now that life has been found on Earth in conditions similar to that which might be encountered on other worlds, scientists think that the chances of finding life have improved.
“This really increases the chance of finding life beneath the surface of Mars,” said Onstott.
Mars was more temperate in its ancient past, and the new findings have scientists speculating that, if life did evolve under those more favourable conditions, it might have survived underground in a similar radiation-powered environment.
“The sorts of ecosystems you could get there could certainly be something like this,” said D’Hondt.
The community of microbes found in the gold mine is dominated by a single as-yet-unnamed strain of bacteria of the group Firmicutes, closely related to specimens recovered from high-temperature sub-oceanic crust and other high-temperature environments. The rest of the community is made up of other primitive bacteria and archaea (bacteria-like single celled organisms).
The microbes found inside the gold mine use sulphur instead of oxygen as the basis of their metabolism, reacting it with molecular hydrogen to produce energy. Bacteria that live without any energy from sunlight have also been found in volcanic aquifers deep underground, but the researchers say it’s not clear whether these ecosystems are either sustainable or totally isolated from food sources originally produced by photosynthesis.
The researchers add that the question of contamination from the products of photosynthesis also separates these bacteria from the famous communities thriving around deep-sea hydrothermal vents known as ‘black smokers’.