Ridley Scott is great at atmosphere and striking visuals. But this movie is so stupid it is nearly incoherent. Supposedly smart scientists do moronic things over...and over...and over. Because if they didn't, they wouldn't get to die in spectacularly gross fashion for our entertainment.
"Hey, there's air here, let's all TAKE OFF OUR HELMETS on this unknown alien world with all these alien corpses lying around. It'll be fine!" "But Bob, somebody who did that yesterday had alien worms come out of his eyeballs and had to be killed with fire..." "Oh, shut up and breathe the sweet air."
"Let's screw." "I wouldn't do you if you were the last man on earth." "Yeah, but the plot requires me to be away from the communications center long enough for two more crewmembers to die horribly." "My quarters, big boy. Ten minutes."
"Oh, look, alien goo. I think I will slip some in a crewmember's drink. Why? No friggin' clue. But perhaps it will have an utterly inexplicable effect that I will somehow be able to predict even though I have been here on this world all of ten minutes, and only a scriptwriter on SERIOUS drugs would imagine it would do any such thing."
"I had major abdominal surgery 2 minutes ago. See how I run!"
This film, like its characters, is too dumb to live.
I haven't seen Prometheus, but your first quote reminds me of Galaxy Quest:
[Fred opens the door after the shuttle lands]
Guy: "Hey! Don't open that! This is an alien planet! Is there air? You don't know!"
Fred: [sniffs the air outside] "Seems OK."