While it is true that building a city under the ocean would be easier than going to Mars, going to Mars isn’t going to stop oceanographic research. One does not cancel out the other. It’s not like we are pulling out funds from researching the ocean so we can go to Mars. There are things still to be discovered under the sea. There are things still to be discovered in space. Both will go on because we have billions and billions of people and some people like studying the oceans and some people like studying space!
Exactly the disappointing truth. It can’t. Since Mars is too small, the core cooled down long ago and therefore the organized magnetosphere doesn’t exist. Put as much atmosphere you want and it will still be blown away and not protect us from dangerous rays from the sun. We can only “colonize” the same way we “colonized” the Moon or the International Space Station: staying indoors!
Terraforming Mars is a long ways off. In fact, it’s highly unlikely that it would ever be possible and since there’s no organized magnetic field on Mars, any life that walked outside would be exposed to lethal radiation from the sun with or without an atmosphere.
That being said, life can evolve even with high amounts of radiation under certain conditions. Over time, life finds a way to exist even in extreme conditions. Evolution would follow a random pattern – the fittest of those would survive and the less fit would perish. Survival of the fittest is what drives Evolution, whether on Earth or on Mars, forward.