Underneath the gold mines of South Africa's Witwatersrand Basin, scientists have discovered ancient, secluded pockets of water that are also home to some of the most isolated extremophile ecosystems on our planet.
To determine how isolated the Witwatersrand's saline groundwaters are, researchers examined a specific type of the element neon dissolved in the waters, which are situated three kilometers below the surface and could date back millions of years.
Says University of Toronto professor and study contributor Barbara Sherwood Lollar of the Witwatersrand groundwaters:
The chemical signatures also don't match those of ocean water or waters higher up in the Witwatersrand Basin, where as in most regions of the crust ground waters show evidence of mixing with surface waters and are extensively colonized by microorganisms [...] We concluded that the deeper waters were the product of isolation and extensive chemical interaction between water and rock over incredibly long geological time scales [...]
We know that this specific neon isotope signature was produced and trapped within the rock at least two billion years ago. We can still find it there today [...] The study shows some of the neon found its way outside of the rock minerals, gradually dissolving into, and accumulating in, fluids in crevices. This could only happen in waters that have indeed been cut off from the surface for extremely long time periods.
Lollar also noted that the life within the Witwatersrand crevices bear a resemblance to other microorganisms found at geothermally heated bodies of water:
Given that they have a genetic similarity to organisms found at hydrothermal vents, we assume this is not a separate origin of life, but instead these organisms arrived from elsewhere to colonize these rocks in ancient times [...] Clearly the long period of isolation affected their evolution. This is one area we hope to explore with continuing research with our microbiology colleagues.