When Barbara Sherwood Lollar sent water samples to a colleague at the University of Oxford for testing, she knew this was no ordinary water. The geochemist had spent much of her career wandering around some of the deepest mines in the world, finding and extracting water that was millions of years old. She waited and waited for results that should’ve come back promptly. So she dialled up the U.K. researcher in charge of the test. “I said, ‘Hey, what’s going on with the samples?’ ” she recalls. “He said, ‘Our mass spectrometer is broken. This can’t be right.’ ” The tests pegged the mean age of the samples, extracted from a mine north of Timmins, Ont., in 2009, at 1.6 billion years old—the oldest ever found on Earth.