On Earth, volcanic eruptions trigger the carbon cycle that accounts for the eventual concentration of calcium carbonate wherever water once existed. On Mars, the absence of calcium carbonate and, even more importantly, the presence of jarosite suggests that the element sulfur may have played a comparable role to that of carbon on Earth. Specifically, Martian volcanoes apparently ejected vast quantities of sulfur dioxide (instead of carbon dioxide released in volcanoes on this planet) where it was eventually dissolved in Martian oceans to form silicates and sulfites including calcium sulfite. At the same time, the presence of calcium sulfite would also have inhibited the formation of carbonates like limestone.

Additionally, this recent observation also offers a logical explanation for how a planet like Mars which is presently far too cold to support liquid water could ever have been warm enough to do so. That answer derives from the fact that just...
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