Water from rocks in a mine is at least 1 billion years old

Ars Technica : Deep below Earth’s surface, sediment is compacted and metamorphosed into hard rock. Hydrothermal fluids that bathe the rocks while they are forming can get trapped in fissures. When those rocks are later uncovered by human mining, the water’s age can be determined by examining the ratios of isotopes of noble gases dissolved in the water. With that method, water from a mine near Timmins, Canada, has been determined to have been trapped between 1 billion and 2.6 billion years ago, making it the oldest known water. The key element in the determination was xenon, of which 9 different isotopes were present. Some of those isotopes point to the water’s hydrothermal origin. Others reflect the atmospheric composition of Earth about 1.5â2.6 billion years ago. And the levels of other noble isotopes, which are the products of the decay of radioactive elements, put the date of entrapment anywhere between 1.1 billion and 1.7 billion years ago. Also present in the water were H ₂ and methane, two compounds necessary for microbial life. That discovery suggests that similar fluids could be preserved on other worlds, such as Mars, and could contain signs of ancient, extraterrestrial life.