Witwatersrand basin has ‘world’s oldest water’
Deep saline groundwaters in the basincould be the world’s oldest water.
Washington: A new study has suggested that deep saline groundwaters in South Africa`s Witwatersrand Basin may have remained isolated for millions of years and could be the world’s oldest water.
Researchers found noble gas neon dissolved in water in three-km deep crevices.
The unusual neon profile, along with the high salinities and some other unique chemical signatures, is very different from anything seen in molten fluid and gases rising from beneath the Earth`s crust, said University of Toronto professor Barbara Sherwood Lollar at the American Association for the Advancement of Science recently.
“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,” she said.
“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,” she added.
“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,” said Lollar.
The study showed that 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, said Lollar.
The discovery adds yet another dimension to what has only recently been recognized as a truly unique environment.
One of these fracture systems contains the deepest known microbial ecosystems on Earth. These are organisms that eke out an existence independent from sunlight on chemical energy that originates from rock.
“These deep microbial communities radically expand our concept of the habitability of the Earth`s subsurface and, indeed, our biosphere,” said Lollar.
“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," she said.
“Clearly the long period of isolation affected their evolution. This is one area we hope to explore with continuing research with our microbiology colleagues,” she added.
The study has been accepted for publication in Chemical Geology.