Ok, it does, but I doubt the atomospheric pressure on Mars was above 73 atm, which is what is required for CO2 to stay in liquid form and not immediately turn into gas.
Ok, but again, I don't think the martian atmosphere was ever above 5 atm. Yes, the martian atmosphere is leaking out slowly, and was possibly much higher than it is now, but not 20x higher.
No, recent as in the last couple years. http://space.newscientist.com/article/dn10740-water-flows-on-mars-before-our-very-eyes.html
Come on, everyone knows that Aliens have to occasionally stop off at uninhabited planets on long journeys to crouch behind rocks safe from the prying eyes of military specialists from other advanced alien cultures. As for a serious answer, Molecules do break down and their component atoms can re-emerge as different molecular structures. We know this just from our own atmosphere, it's just with our own we have so many sources of pollution and "filtration".
This isn't really pseudoscience; it is is honest-to-goodness ordinary science. What appears to happen is that periodically underground reservoirs of ice melt and cause a flow of water; this water boils in the thin atmosphere of Mars, and by the time it has travelled a few hundred meters, it evaporates. Some of the larger flow channels on Mars were probably caused by the same mechanism. All that is missing is a mechanism for causing the melt -the debacle - in the first place.
