Newfound bacteria in South Africa are fueled by radiation. The scientists who discovered it summarize the discovery by saying:
“The bottom line is: Water plus rocks plus radiation is enough to sustain life for millennia.”
Most subsurface microbial ecosystems examined to date (including subseafloor sediments, deep-sea hydrothermal vents, terrestrial sedimentary aquifers, and petroleum reservoirs) ultimately depend on sunlight. …
To determine the long-term sustainability of a deep terrestrial environment, we examined the microbial diversity and metabolic activity of a 3‑to 4‑km-deep fracture in the 2.7‑billion-year-old Ventersdorp Supergroup metabasalt, in which fracture water ages of tens of millions of years, abundant abiogenic hydrocarbons, and radiolytically produced H2 have been reported.
The only energy source that appears to have reached any of the material there is radiation from the surrounding rocks. They estimate that the bacteria first colonized the rock between 3 and 25 million years ago, and have relied on hydrogen gas and sulfides produced from the surrounding rock. The authors conclude that “the deep crustal biosphere may be energy-rich, is not approaching entropic death, and is capable of sustaining microbial communities indefinitely by geological processes.”
Who knows what other complex communities of bacteria survive in odd corners of earth, or on other planets.