The liquid was discovered deep down in a mine in Canada in 2013 and is about 1.5 billion years old.
At the same site, University of Toronto scientists have found a deeper source of water that is at least 500 million years more ancient.
The work was presented at the American Geophysical Union Fall Meeting in San Francisco.
These things are flowing at rates of litres per minute – the volume of the water is much larger than anyone anticipated.
” The first pool of ancient water was discovered 2.4km-down in a copper, zinc and silver mine.
“And we took advantage of the fact that the mine is continuing to explore deeper and deeper into the earth.
” This new investigation led by Dr Oliver Warr, from the University of Toronto, found water at a depth of nearly 3km. And tests have revealed that it is at least two billion years old.
It provides scientists with a unique insight into the history of our planet, and gives a glimpse at the life that was present at this time.
The researchers have found chemical traces left behind by tiny single celled organisms that once lived in the fluid.
“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. This isn’t just a signature of very modern microbiology.”This has to be an indication that organisms have been present in these fluids on a geological timescale.