The freezing point is -73 C. You could have a cold Mars, yet still have liquid. What water may have been present would form sulfurous acid, and later, sulfates. The heavier gas and liquid SO2 would have been more resistent to solar ablation. When the seas had eventually thinned or disappeared, the seafloor would have been exposed to higher levels of oxygen, allowing the SO2 and acid to react with the rocks. This mechanism, resulting in sulfate deposition, could have completely scrubbed the atmosphere of the sulfur dioxide if oxygen was in excess. I give less credence to this theory than to water as the primary fluid, but it seems interesting. Some mix of water and SO2 seems plausible, but which was in excess? Io shows how odd a planet or moon can be in composition, much like a distillate. Drink in the Io shine.

Sulfur dioxide, less thermally stable than CO2 and water, could only form farther out from the sun in cooler temperatures than the Earth zone. Sulfur, as a fairly light element, was centrifugally distilled farther out in the planetary disk. The moons of Jupiter show the same basic stratification, with denser elements closer in, but starting with a lighter mix than the solar planetary disk. Io's atmosphere is principally SO2. Sulfur would have been most abundant, relatively, in the region somewhere between Earth and Jupiter, perhaps in the region of Mars.

Speaking of distillates, most of the theories I have seen propose that the Earth got most, or all, of its water from comet impacts. I am skeptical, and think this was just a late stage supplement. My conestoga model of the proto planetary disk is that it was basically a type of solar wind versus gravity distillation. Earth formed in the dense rock zone, but also with much water and CO2, so it was steamy and had hydrates from the beginning. Pictures in Time/Life books show the early Earth as a sea of lava, molten rock everywhere with meteorites filling the skies. How likely really is that? Without some super thick and cloudy atmosphere to trap that hellish heat, could it really have been that hot across the whole surface? Wouldn't that heat have driven off much of the atmosphere? Wouldn't such a thick atmosphere burn up most of the small to medium size meteorites at high elevation where the heat would radiate to space? These books describe how the Earth finally cooled down, and a great flood (like Noahs...) finally descended and the oceans condensed out of the atmosphere in a cataclysm. Most everyone takes this picture as the undisputed (Gospel...) Truth, and I did too, at first. However, the proto Earth likely began as a small, relatively cold body, and only later underwent much heating. Sure the overall volatile content of the Earth shows that it underwent great heating, and complete melting of the core and everything else. But these rocks were recycled tectonically. Overturned and subducted like boiling fudge. None of the possible proto crust survives to tell its thermal history. The heat from Thorium decay is what has kept the Earth's core molten. Could the Earth, and Mars, have had liquids, or even ices in places throughout their history? At least I question this possibility, and invite debate.