Scientists have discovered the oldest known water on Earth in an ancient pool in Canada. The water, which was untouched for 2 billion years, was found 3 kilometers (1.86 miles) underground.

2-Billion-Year-Old Water

In 2013, researchers found water dating back about 1.5 billion years at the same site, an underground tunnel at the Kidd Mine in Ontario, but after searching deeper, they found an even older source of water buried underground.

After conducting an analysis of the gases dissolved in the ancient groundwater, which include neon, helium, argon and xenon, the researchers dated the liquid to at least 2 billion years, making it the oldest known water in the world.

The researchers were also able to find chemical traces left behind by tiny unicellular organisms that once lived in the water.

"The microbes that produced this signature couldn't have done it overnight. This isn't just a signature of very modern microbiology," study lead Barbara Sherwood Lollar from the University of Toronto told BBC News. "This has to be an indication that organisms have been present in these fluids on a geological timescale."

Possibility Of Alien Life Living Underground On Mars

The discovery, which was presented at the American Geophysical Union Fall Meeting in San Francisco, offers clues about the possibility of alien life residing within the underground pockets of water on planet Mars.

NASA has been sending rovers to the planet with the hope of finding evidence of extraterrestrial life. Studying water on Earth such as the one discovered in Canada may offer hints on where life may be found on the red planet and elsewhere in the solar system.

In an earlier study that looked at the 1.5-billion-year-old water discovered 2.4 kilometers underground, researchers have found evidence that the ancient water has its own independent life support system.

What this means is that it is possible that exotic life has been evolving underground, totally independent from life on the surface for billions of years without sunlight or atmospheric oxygen.

If microbial communities can evolve in parallel to life as we know it deep below the surface, it is possible that the same thing can happen on the red planet.

"Because this is a fairly common geological setting in early Earth as well as modern Mars, we think that as long as the right minerals and water are present, likely kilometers below the surface, they can produce the necessary energy source to support the microbes. I'm not saying that these microbes definitively exist, but the conditions are right to support microbial life on Mars," said Long Li from the University of Alberta.