[just_boost_it]

Like, without that inert gas there would have to be something else. Being in a pure oxygen environment for a prolonged period has health impacts to many animals including us. Anything even remotely flammable, like paper, wood, sugar, would burn uncontrollably with the slightest spark.

If you didn't have nitrogen you would need another inert gas to make up 80% (or whatever) of the atmosphere you were going to make.

[adastra22]

For the most part, partial pressure is what matters, not absolute pressures. The only contribution inert nitrogen has to life is raising the boiling point of water. But on a frigid planet like Mars that’s not going to be an issue.

Being in a pure oxygen environment does not have a long term impact on animals… if the pure O2 environment is 0.21 atm oxygen. There’s a long history of biological experimentation done by space agencies on this, and the Apollo missions operated on a 0.2 atm pressure for the duration of their missions. Apollo 1 famously had trouble not because it was pure O2, but because it was 1.2atm O2.

There is no reason you need backfill inert gasses to have 1.0 atmospheres.