It’s probably a good guess that most of us don’t think too much about where our water comes from or just how old it might be, but one thing we do know – securing this vital resource and using it in a sustainable way is necessary to life on this planet.
In a new study published in the online journal Nature on Tuesday, researchers set out to determine how old the Earth’s groundwater really is. The findings were presented at a European Geosciences Union meeting in Vienna, Austria.
The planet’s groundwater is usually found at depths of more than 250 meters (820 feet) under the Earth’s surface. This water is called “fossil water,” or sometimes, “paleowater” because it trickled down through the porous rocks to be stored in vast underground reservoirs called aquifers thousands of years ago. This water has been around since before the age of the mammoths, with some of it dating to 12,000 years ago.
People today use this fossil water to irrigate their crops and as drinking water. And because this water initially infiltrated into the underground reservoirs long ago and often under climatic conditions different from the present, it has always been assumed to be pristine and without contamination.
Technology, using isotopic signatures aided the scientists in determining the age of the fossil waters in aquifers. And what the team found was surprising. According to study co-author Scott Jasechko, of the University of Calgary. Deep wells, believed to bring only pure, ancient water to the surface, are “vulnerable to contaminants derived from modern-day land uses.”
The study used the radiocarbon and tritium content of the water to distinguish if it was fossil water or “young” groundwater. Basically, tritium, a short-lived isotope of hydrogen, can only be found in young water because it has been more recently exposed to the atmosphere and surface, tainted by nuclear tests done back in the 1950s.
Radiocarbon, on the other hand, takes nearly 6,000 years to decay, so it is less abundant in fossil water. Analysis showed that “most of the groundwater under our feet is surprisingly old,” said study co-author James Kirchner of the Swiss Federal Institute of Technology in Zurich.
Almost half of our groundwater, according to the study, dates from 12,000 years ago, or even more. “The assumption would be if your groundwater comes from a time when mammoths were roaming the Earth, that those mammoths did not have chlorinated hydrocarbons,” Kirchner explained.
So this means that if the water was present before the age of the Industrial Revolution, there is no way it could possibly have modern-day contaminants. And this leads to the surprising findings. The team found that about half of “fossil water” wells they studied contained detectable levels of tritium, indicating the presence of younger water.
“This observation questions the common perception that fossil groundwaters are largely immune to modern contamination,” concluded the study. And it also raised a couple of worrisome issues. Jasechko points out that not only can fossil water be exposed to modern-day pollution, but it could take millennia to replenish it once it is used up.
“Conserving groundwater for future generations is important and requires us to consider time spans beyond the typical political or land management timescales of years or decades,” he added. “Securing safe drinking water remains a key challenge for hundreds of millions of individuals around the globe.”
For further reading on groundwater and aquifers:
One of world’s largest water sources is contaminated
One-third of the world’s groundwater basins are in distress
Call for Nestlé to pay for groundwater extraction
