What first comes to mind when I say the word “old”? The Model T, which came out in 1908? The dinosaurs that first roamed the earth about 230 million years ago? My kids would say – me!
How about water? Scientists have confirmed that gold miners in Ontario discovered water at least 1.5 billion years old while drilling into bedrock. The water was actually part of ancient oceans. The recent report suggests that the water seeped from above ground through the earth, eventually finding itself trapped in the bedrock.
We have historical documents on the creation of the Model T, we’ve dug up dinosaur bones, and somewhere (maybe on papyrus) you could find my birth records. But how do scientists determine the age of water?
There are actually a number of different options. What’s measured isn’t the age of the water molecule itself, but the age of the water within the water cycle. That can be determined by the ratio of certain isotopes through a process called isotope hydrology. The techniques are used for water-use policy, mapping aquifers, conserving water supplies, and controlling pollution.
Water molecules carry unique fingerprints, based in part on differing proportions of the oxygen and hydrogen isotopes that constitute all water. Isotopes are forms of the same element that have variable numbers of neutrons in their nuclei. Air, soil and water contain mostly oxygen 16 ( 16O). Oxygen 18 ( 18O) occurs in approximately one oxygen atom in every five hundred and is a bit heavier than oxygen 16, as it has two extra neutrons. From a simple energy standpoint this results in a preference for evaporating the lighter 16O containing water and leaving more of the 18O water behind in the liquid state (called fractionation). Thus, seawater tends to be richer in 18O, and rain and snow relatively depleted in 18O. Carbon 14 dating is also used as part of isotope hydrology as all natural water contains dissolved carbon dioxide.
Beyond just being interesting, the discovery could potentially be out of this world. The samples also contained hydrogen, which is food for some microorganisms. They’re being tested now for evidence of microbes, and scientists hope to have results within a year. If microbes are found, they could give us unique insight into the earliest forms of life on earth and the potential for life on other planets. It looks like those miners may have found something more valuable than gold!