And doesn't Mars have those Polar Ice Caps, and evidence of River Beds.
It also has salt residues that can only be formed naturally by tidal currents of liquid water. It's pretty much fact that Mars, at one point, had liquid water.
Mars might've been a Future Earth, that had some sort of Genocidal Disaster, wiping life from the surface (Meteor, Volcanic Activity, other Aliens) heck while we were still curly blobs in the pool of life. Mars could've been decades ahead of were we are now.
"Decades"? Decades are a blink of an eye, when you consider the real age of the solar system, let alone the entire age of the universe. What is a few tens of years when you're talking about billions?