"Mars does not have an atmosphere and does not have a magnetic field today, so the planet doesn't hav..." — David Grinspoon

What we should really be thinking about is what it would look like for a truly intelligent technological species to be interacting with their planet's atmosphere.

Radiation is one of the important factors in evolution. It causes mutation, and some level of mutation is actually good for evolution.

I'm an astrobiologist, and I come from a planetary science background, so in a very broad sense, I study the evolution of planetary environments.

Earth is going to lose its oceans in the future, just as Venus did in the past. How long planets retain their oceans is a function of distance from the sun, all other things being equal.