On a planet with an unchanging amount of water, and a pretty good idea where all of it is, scientists have uncovered something startling up in Ontario, Canada. Water locked deep under Canadian bedrock was slowly seeping out of tunnels that gold miners were drilling in the hills. When a few British scientists caught word, they asked to sample the water. They discovered it was more than one billion years old.
How do you test water’s age? Not easily, it turns out. Generally you need a large amount of water, and a laboratory to do complex chemical analysis. There are a few ways to date water, but the most common is by testing isotopes of hydrogen and helium. Both are found in large supply in the universe, and fortunately for chemists, both also decay at certain known intervals. Measuring those intervals essentially gives you a rough estimate of how long the water has been stagnant, without the introduction of new hydrogen or helium.