Originally posted by bluewaterrider
If we're talking specifically about that fight "Dark" Kara had with Martian Manhunter again, it's important to keep in mind that the locale wasn't really out in the middle of space somewhere.The location was the crater on the Moon that then housed the Justice League of America (JLA) Satellite Base.
Which is significant, because, within range, that base generated a breathe-able atmosphere for people in and around the area.
A final proof of this is that, after going back to the crater, and after J'onnz's assault, and after Dark Kara chokes J'onnz into submission, and AFTER Light Kara then intervenes, the JLA finally rallies and confronts the merciful but wayward girl.
The members include Blace Canary and Flash, just demonstrated to, in fact, need air to breathe, even on the Moon, but there are no visible barriers save the perimeter of the crater to mark this safe area.
Dark Kara takes off and seems unimpeded by anything, Light Kara takes right off after her, and the JLA members talk among themselves about what action should be taken next, if any.
At any rate, the premise, likely, again, borrowed from X-Men, appears reasonably well-supported: the JLA Satellite produces sufficient air to keep man and alien alike breathing -- as long as they stay within the satellite's crater.