Or what if he went way back in time, before the earth had a breathable atmosphere?

Death within seconds, as the craft shot beyond breathable atmosphere.

On the other side of the shell, there was atmosphere, cold but breathable.

They would not get into the naturally breathable atmosphere for several minutes after that.

But here on P2 we had the advantage of a nearly breathable atmosphere.

And even that one does not have a breathable atmosphere.

First a breathable atmosphere had to be created within the dome.

"And they'll have a breathable atmosphere in a decade, I hear?"

It turns out to be very similar to Earth, with a breathable atmosphere.

On final approach, an area with breathable atmosphere is detected.