What Is the Oldest Water Ever Found on Earth?

The Oldest Water on Earth

The oldest free-flowing water ever discovered on Earth was found 2.4 kilometres underground at the Kidd Creek Mine near Timmins, Ontario, Canada — sealed inside ancient rock for between 1.5 and 2.64 billion years, long before complex life existed on this planet.

Where Was It Found?

The Kidd Creek Mine is one of the deepest base-metal mines on Earth, descending more than three kilometres below the surface. It is primarily a copper and zinc operation, and the surrounding rock belongs to the Precambrian Canadian Shield — some of the oldest geology on the planet, dating back over 2.7 billion years. In 2016, geochemist Barbara Sherwood Lollar and her team at the University of Toronto discovered water trickling from cracks in these ancient rocks at the 2.4-kilometre level. Unlike surface groundwater that might seep down over centuries, this water had been completely isolated, locked inside microscopic fractures in rock that formed before animals, plants, or even complex single-celled organisms existed on Earth.

Why Is This Water So Unusual?

The water is several times saltier than the ocean — so dense and mineral-rich that a researcher who tasted it described it as almost undrinkable. That extreme salinity is part of what allowed it to remain liquid and chemically stable for billions of years rather than freezing or evaporating. Age dating was confirmed through the analysis of noble gases dissolved in the water, particularly xenon, helium, and neon isotopes, which act like a chemical clock, building up at predictable rates from radioactive decay in the surrounding rock. These signatures left no doubt: this water had been cut off from the surface world since before the Cambrian explosion, before dinosaurs, before fish, before almost everything.

Could Something Be Living Inside It?

This is where the discovery becomes truly extraordinary. Over billions of years, radioactive decay of uranium, thorium, and potassium in the surrounding Precambrian rock generated hydrogen inside the sealed water. Scientists detected elevated levels of both hydrogen and methane — two chemical compounds that can serve as energy sources for microbial life. On the surface of Earth, hydrogen-fed microbes thrive in some of the harshest environments imaginable. The chemical conditions inside the Kidd Creek water are consistent with supporting a similar community of microorganisms that have lived in complete isolation for geological timescales. Whether life is actually present has not yet been conclusively confirmed, but the chemical fingerprint strongly suggests it is possible — and perhaps likely.

What Does This Mean for Life on Mars?

The implications extend far beyond Ontario. Mars has ancient, fractured bedrock beneath its surface, and scientists now believe that similar pockets of ancient fracture water could exist there today. If microbial life can survive for two billion years inside isolated water on Earth, sustained only by the slow chemistry of radioactive rock, then the same process could theoretically be underway beneath the Martian crust right now. The Kidd Creek discovery has become a cornerstone reference point in astrobiology — the science of searching for life beyond Earth — and has shifted scientific thinking about where in the solar system life might be hiding.