The first known organisms that live totally independently of the sun have been discovered deep in a South African gold mine.
The bacteria exist without the benefit of photosynthesis by harvesting the energy of natural radioactivity to create food for themselves. Similar life forms may exist on other planets, experts speculate.
The bacteria live in ancient water trapped in a crack in basalt rock, 3 to 4 kilometres down. Scientists from Princeton University in New Jersey, US, and colleagues analysed water from the fissure after it was penetrated by a narrow exploratory shaft in the Mponeng gold mine near Johannesburg, South Africa. The shaft was then closed.
“Sulphate and hydrogen gas are generated from geological processes. Microbes use these nutrients to live,†explains Lin.
Uranium and other radioactive elements in the rock emit radiation that shatters water molecules, producing high-energy hydrogen gas that is able to cleave chemical bonds.
The bacteria exploit this hydrogen gas to turn sulphate (SO4) molecules from the rock into hydrogen sulphide (H2S). It is the energy-trapping equivalent of photosynthesis. The energy of radiation, which makes hydrogen gas energetic enough to form these bonds, replaces the energy of the Sun.
A study of the inert gases in the sample, such as xenon, show that the Mponeng water has been isolated from the surface for 20 million years, says Lin.
Gold mine holds life untouched by the Sun * 19:00 19 October 2006 * NewScientist.com news service * Debora MacKenzie
