In 2016, geologists studying a Canadian mine made an incredible discovery. At a depth of about 3 kilometers (1.8 miles), they found flowing water, which tests revealed to be between 1.5 billion and 2.64 billion years old. Having been isolated for all this time, it was the oldest water that had been found on Earth. 

“When people think about this water they assume it must be some tiny amount of water trapped within the rock,” Professor Barbara Sherwood Lollar, who led the team, told BBC News. “But in fact it’s very much bubbling right up out at you. These things are flowing at rates of liters per minute – the volume of the water is much larger than anyone anticipated.”

The team found traces that indicated life had once been present within the water.

“By looking at the sulphate in the water, we were able to see a fingerprint that’s indicative of the presence of life. And we were able to indicate that the signal we are seeing in the fluids has to have been produced by microbiology - and most importantly has to have been produced over a very long time scale. The microbes that produced this signature couldn’t have done it overnight," Sherwood Lollar said. “This has to be an indication that organisms have been present in these fluids on a geological timescale.”

Without light, the microbes survived using substrates produced from radiation.

“The sulfate in this ancient water is not modern sulfate from surface water flowing down. What we’ve found is that the sulfate, like the hydrogen, is actually produced in place by reaction between the water and rock," Long Li, assistant professor in the University of Alberta’s Department of Earth and Atmospheric Sciences, said in a press release. "What this means is that the reaction will occur naturally and can persist for as long as the water and rock are in contact, potentially billions of years."

While the discovery had implications for finding life elsewhere on Earth as well as out there in the Solar System, what everyone on the Internet always wants to know is: what does the forbidden drink taste like? Amazingly, we have an answer for that.

“If you’re a geologist who works with rocks, you’ve probably licked a lot of rocks,” Sherwood Lollar told CNN. While not a rock, she still gave the water a try, tasting it off her finger. She was looking for a salty taste, with saltier water tending to be older. Much to her delight, the water was "very salty and bitter" and "much saltier than seawater." This isn't altogether surprising, given that it had been aged for over 2 billion years.

The paper was published in Nature in 2016.