Groundwater, hidden beneath the Earth's surface, is an essential resource for more than a quarter of all Canadians, serving as their primary source of drinking water, irrigation for farming, and support for various industries like manufacturing. While its importance is undeniable, most Canadians do not fully grasp the value of this underground water reserve. Professor Oliver Warr, a new Assistant Professor in the Department of Earth and Environmental Sciences, is dedicated to understanding the nature, distribution, and transport of groundwater in a broad range of environments, and the role these fluids have in modern society.
With a total volume second only to the oceans, these underground reservoirs of water are not confined to channels or depressions in the same way that surface water is concentrated in streams and lakes. Instead, they exist almost everywhere underground, permeating through the spaces between particles of rocks and soil, or trapped within crevices and cracks in the rocks themselves. Fluids located in these cracks and fractures can remain isolated from the outside world for extremely long time periods, undergoing chemical changes as they interact with surrounding rocks, causing them to become extremely saline.
Determining exactly how long these deep and saline fluids have been trapped can be a challenging task. Traditional methods like carbon-14 and tritium dating are limited to waters younger than 50,000 years. However, all rocks contain traces amounts of uranium, thorium, and potassium, which naturally decay over time, producing noble gases such as helium, neon, argon, krypton, and xenon, that diffuse and accumulate in these waters. By measuring the noble gas content of the water, Prof. Warr’s team can accurately estimate how long the water has been trapped, far beyond the 50,000-year limit.
Professor Warr’s groundbreaking research, in collaboration with the University of Toronto and Oxford, has taken them to multiple active mines around the world, including Timmins, Ontario, and South Africa, to collect samples of these mysterious underground fluids directly from fractures in the rock. In a notable study published in 2018, water samples from three kilometres below the surface in an active mine in Timmins revealed groundwater over a billion years old! Their recent publication in Nature Communications unveiled groundwater samples from a South African gold mine with unprecedented concentrations of radiogenic products, including a novel noble gas isotope never before observed in a natural setting. Using noble gas measurements, they determined that the groundwater had a residence time of more than a billion years. These findings suggest that groundwaters can be preserved in the deep continental crust on billion-year or more geologic timescales and that they may be more prevalent globally than previously thought.
The implications of these ancient fluids are far-reaching. From a resource perspective, understanding the production and accumulation of helium is critical for advancing medical and industrial applications. Moreover, these groundwaters shed light on alternative models of habitability. While most life on Earth uses the Sun as an energy source, microorganisms residing three kilometres below the surface do not have access to sunlight and need to find other sources of energy. Instead, they rely on the same natural radioactive decay processes, which not only produce noble gases but can also generate food such as hydrogen. Understanding the persistence of these habitable fluids can help researchers understand and explore alternative habitability models applicable beyond Earth, informing exploration strategies for other planets like Mars.
In essence, Professor Warr's research not only unveils the secrets of Earth's ancient groundwater but also opens new avenues for understanding habitability and resource utilization both on our planet and beyond.
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