“It’s exciting on about five different levels,” said Barbara Sherwood Lollar, a professor of Earth Science at the University of Toronto who was part of the team that made the discovery. “It’s a part of the planet where we have waters of a nature we never thought possible.” The team’s analysis of the water has been published today in the journal Nature.

The water exists in a network of interconnected pockets where the rock has been fractured by movements in the Earth’s crust over geologic time. It is abundant enough that litres of can be seen flowing from mine boreholes.

Prof. Sherwood Lollar and her colleagues have determined that gasses in the water are similar to those found in deep sea vents, suggesting that certain forms of microbial life could survive there without requiring any energy from the sun. Samples of the water are now being examined by researchers outside the team who are looking for signs of microorganisms. If such microbes are found their presence would signal the existence of a "Galapagos of the deep," Prof. Sherwood Lollar said — isolated ecosystems that have been free to follow different evolutionary pathways independent from the rest of life on Earth. Their existence would also bolster the theory that life could be flourishing today deep below the surface of Mars or on other distant planets where conditions at the surface are inhospitable.

The volcanic rock within which the water was found is “very similar to Martian rocks,” said Greg Holland, a geochemist at Manchester University in the UK who helped analyze the chemical signature of the water. “Mars when was much more habitable, three to four billion years ago, life there went underground and has carried on living happily ever since.”

Among the key ingredients in the water that Dr. Holland and others measured are isotopes of noble gases, including helium, neon, argon, krypton and xenon. The gasses are produced by the radioactive decay of heavier atoms in rock but are chemically inert so their accumulation in the water can be used to measure how long the water has been sealed off.