The next reason is, Mars could be colonized because we could bring oxygen tanks, and save them for until we land on mars safely, we could start anytime. For a third reason, Mar's Atmosphere has some oxygen, 95.3% CO2, and 2.7% nitrogen. The oxygen level is very small, but with enough oxygen tanks, to even spend a day on mars, then we could see what we're going to need to do if we colonize forever.