Living-on-Mars

It's not going to happen. Probably ever. Many years ago, I worked testing fans. One thing we had to deal with was air pressure. 14.7 PSI is about 2,000 pounds per square foot. The top of Mt Everest is referred to as "the death zone" because if you stay in that reduce atmosphere too long, you die. There is not enough oxygen humans need to sustain life.

Now, you could live in 100% oxygen at a much lower pressure, but if there was ever a fire, everything burns. NASA found that out, much to their dismay. SO, if we have a dome, 200' in diameter, and only 500 3-1/2 psi (that'd be shaving it really close) the pressure trying to lift that dome up would be 83 tons. You could not keep the thing on the ground -- or more realistically, keep it from leaking.

Maybe you've noticed that there are no large rooms on the ISS. There are longer tubes. So that the air pressure inside doesn't blow them apart. And the air pressure in the ISS is 14.7psi, just like here on earth. It could be lower, but you don't want to reduce oxygen all that much. But you also have to consider fire. It's worth it to NASA and everyone to maintain conditions as they are here on earth.

On Mars, that would increase the force trying to lift the dome from 83 tons to 340 tons.

A similar argument can be made for living in space. The tube structure of the ISS will always be used. That makes for a pretty cramped life. Inside the ISS it's already cramped. You're just not going to have a large community with that size restriction.

AND, for both cases, there's the problem of, where's the food going to come from? Lots of plants don't do all that well when there's hard solar radiation, that's not insulated by earth's atmosphere + magnetic shield. And this is just a quick look at 2 obvious problems.