From South Africa comes news of a striking find: bacteria living two miles beneath the surface and, more significantly, dependent only on the sulphur and hydrogen produced by geological processes rather than on the energy of the Sun. That life should form in such remote venues seems extraordinary, but the finding gives credence to the belief that similar microorganisms might have evolved on other worlds right here in our own Solar System.
Sure, we’ve found life in some hostile places before, including ocean vents and petroleum reservoirs, but their biological processes can all be traced at least partially back to the Sun, which provided the energy source for photosynthesis and therefore produced the needed nutrients for life. This new find, uncovered in a rock fissure that intersects the Mponeng gold mine near Johannesburg, uses radioactive decay as its power source, converting water molecules into hydrogen and ultimately producing hydrogen sulphide out of sulphate molecules in the rock.
Here’s Douglas Rumble (Carnegie Institution) on the process:
“We also believe that the sulfate used by these creatures is left-over from ancient groundwater mixed with ancient hydrothermal fluid. We can detect that because the chemical signature arises from interacting with the fracture’s wall rock. It is possible that communities like this can sustain themselves indefinitely, given enough input from geological processes. Time will tell how many more we might find in Earth’s crust, but it is especially exciting to ponder whether they exist elsewhere in the solar system.”
The microbes seem to have survived for tens of millions of years in this mode. Is there a similar kind of geologically-fueled life under the ice crust of Europa or in even more exotic environments further out in the Solar System? For that matter, how many other such communities exist elsewhere in our own planet’s crust? The paper is Li-Hung Lin et al., “Long-Term Sustainability of a High-Energy, Low-Diversity Crustal Biome,” now running in Science Vol. 314 No. 5798, pp. 479-482. An abstract is available.