Note that while the cultures were outside the Space Station, they were in containers simulating the conditions of Mars, so it doesn't seem like they were in the vacuum of Space itself, unless I've missed something in the article?
0.0060 atm (0.6%), to be exact [1].
https://en.wikipedia.org/wiki/Atmospheric_escape
https://en.wikipedia.org/wiki/Future_of_Earth
What an interesting, but harrowing existence to be a part of. I don't expect humanity to last that long, but even if we did, then those would be quite the obstacles.
Life itself started about 3.5 bn years ago. So we’re well beyond the half-time of life on this planet.