AstronomyTeacher

An analysis of the surface of Mars shows that some of the gullies were formed under conditions identical to the present condition of Mars. Since Mars has been the way it is for a long time, that makes an inference which I don't think is necessarily required to be true: that water flows on Mars are relatively recent. It would be better in my opinion to argue that based on the amount of degradation of the flow structures due to erosion, they must have occurred relatively recently. Mars, after all, does have weather, wind, and sandstorms, which can alter the surface.

SPACE.com -- Water Flowed Recently on Mars, NASA Scientists Say