Above: Strata rocks line an ancient lake bed on Mars, as captured by Curiosity. Credits: NASA/JPL-Caltech/MSSS

This is a question that I’ve had trouble getting a straight answer to. Yes, there is frozen water on Mars. Yes, there is much evidence that it once flowed as liquid water across the planet. But are the more-than-ancient riverbeds lined with calcium carbonate deposits? We’re not sure.

Why is this an important question?

Imagine a colony on Mars. Those who make that journey from Earth will have a limit to what they can bring along. If we want to continue printmaking traditions on Mars, perhaps the planet itself can offer up some supplies—namely, lithography stones.

Lithography stones are made of limestone, a form of calcium carbonate. On Earth, the chemical is dissolved in most bodies of water, originating (for the most part) from animal life. Think of shells washed up on a beach: these are animal-made constructions of calcium carbonate. Recently, scientists have been studying carbonate structures deep in the ocean created by ancient (but extant) microbes. Limestone deposits occur when a reaction in a body of water causes calcium carbonate to precipitate to the bottom and settle, creating a layer of stone.

So far, we have not found life on Mars, but it’s possible that non-organic calcium carbonate exists on Mars, once dissolved in its once-flowing waters. Perhaps future colonists will carve these Martian arroyos and start a new chapter in lithographic printmaking.