A message in a very old bottle
Deep beneath the Canadian Shield, in the Kidd Creek Mine near Timmins, Ontario, scientists have found water that has been trapped in rock fractures for billions of years. This is not a small, isolated pocket; the ancient water flows from boreholes at rates of liters per minute. The initial discovery in 2013 was of water dated to 1.5 billion years old, found at a depth of 2.4 kilometers. A subsequent discovery in 2016, at a depth of nearly 3 kilometers, pushed the age back to at least 2 billion years.
The Kidd Creek Mine is the world's deepest base-metal mine, excavating copper and zinc from a 2.7-billion-year-old volcanogenic deposit that was once ancient seafloor. The immense pressure and near-impermeable nature of the rock have kept this groundwater isolated from the surface water cycle for much of Earth's history. A team led by geochemist Barbara Sherwood Lollar from the University of Toronto analyzed the water's contents to determine its age. The method involved measuring the concentration of dissolved noble gases—helium, neon, argon, and xenon—that accumulate in the water over geological time from interactions with the surrounding radioactive rock. The specific isotopic signatures of these gases act as a clock, revealing how long the water has been sealed away.