When I was in high school, just beginning to think about what to study at university, they’d found for the first time in the deep, dark parts of the ocean bottom the hydrothermal vents.

And this was changing our understanding of the nature of life on the planet, the fact that there were chemosynthetic organisms, or microorganisms deriving their energy for life not from sun’s energy but from the chemistry of water-rock reaction.

What our work has done is taken that another step, moving away from the ocean floors to the exploration of the continents. We work all over the world, but one of the most important localities for these kinds of rocks is the Canadian Shield. In some of the sites, they’ve found water that pushes back our understanding of how old groundwater can be, because some of these waters actually have residence times on the order of billions of years. Most of the oldest water that has ever been proposed to have been found is maybe 100, 200 million years old.

The other very important thing about this water is that it is very salty. And what that means to us is, being salty, it is also full of all kinds of chemical energy that may be able to support life in these kinds of systems just as we’ve seen on the hydrothermal vents of the ocean floor. Understanding where we see life and where we don’t see life in the deep, salty waters and ancient rock on our planet will help us design strategies for looking for life, or evidence of past life, on the deep, salty waters and the ancient rocks of Mars.

And so if we’re looking for life on Mars, we understand now that either if life ever arose and then became extinct, or if there’s any evidence that there’s still some microbial life present on our sister planet, that that life is likely deep within the planet, protected from the very harsh surface environment.