How we cite our quotes: All quotations are from Alien.
Quote #1
ASH: It's almost primordial. There's inert nitrogen, high concentration of carbon dioxide crystals, methane. I'm working on the trace elements.
The keyword in this quote is "primordial," a word that means "pertaining to the origin or beginning of something." By this, Ash means that it represents a time when Earth was first forming and when the nature of our planet was at its most violent. By our standards, it was a time when nature was not compatible with human life.
Quote #2
KANE: A cave. A cave of some sort. I don't know but it's like the goddamn tropics in here.
The cave Kane is discussing is hot, humid and layered with mist. It brings to mind instances of other works of art dealing with an entrance into violent nature and away from civilization—like, say, Joseph Conrad's Heart of Darkness.
Quote #3
DALLAS: Haven't seen anything like that except molecular acid.
BRETT: Must be using it for blood.
PARKER: It's got a wonderful defense mechanism. You don't dare kill it.
Talk of "defense mechanisms" makes us think about Charles Darwin's idea of natural selection. We humans have been the dominant species on our planet for a decent chunk of time. But here, the human characters are playing the evolutionary equivalent of an away game.