Geologists have discovered 1.2-billion-year-old groundwater about 3 km below surface in Moab Khotsong, a gold- and uranium-producing mine in South Africa. This ancient groundwater is enriched in the highest concentrations of radiogenic products yet discovered in fluid. The discovery have implications beyond Earth, where on rocky planets such as Mars, subsurface water may persist on long timescales despite surface conditions that no longer provide...
