How was the Alien alive for so long in the 1st Alien movie

First, the juggernaut's cargo hold had a stasys field over the eggs, to keep them safe before deployment, also now implying that ship was sabotaged. [i]Book and movie are clear on that, so the stasys field kept them alive and protected (alas telling how advanced and sturdy their tech is)[/i] Second, different beings, although related. The ones on that millitary cargo vessel were bioweapons ready for deployement when that ship got compromised, and the xeno we see is product of whatever they were working on that installation, maybe even a decayed/spoiled product. Third, if that squid thing follows the facehugger model, it would just move aside and die away...

First of all, in Alien it is the DERELICT. The JUGGERNAUT is the ship we see in Prometheus. Not the same ship. Just wanted to clear that up :-D Now, is the Alien you are talking about the facehugger that attaches itself to Kane? If it is, we are led to believe that they can stay dormant and alive for many thousands of years until a host happens by. The original ALien that popped out of Kane's chest was intended by Dan O'Bannon, the original writer of ALIEN, to have a 4 day lifespan, which was why they had to get it off the ship before it died and bled acid all over the place, but since it was never put onto film you have to dig around a bit for the information. Google is your friend ;-)

The Squid was basically a evolution of the Xeno. The Squid and Face Hugger had the same task and that is to find a host and implant a embryo inside them. Once the Squid and Face Hugger accomplish this task they then just die. The Deacon is a evolution of the Xeno that contains Human DNA the Deacon is larger than a Chest Buster maybe because the Squid was larger than a Face Hugger. As for the Derelict well its a Derelict Juggernaut that had been on LV 426 for thousands of years.

The Deacon also came from the substantially larger Engineer, which may explain its greater size in part.

Humm, chosen to be not noticed, but I endure... Again, first what we call Juggernaut is not the ship's name, but its class so to speak, so The Juggernaut in Alien is a derelict ship from that Class, WHICH had a cargo hold full of bioweapons primed to be used in a conflict THAT were stored under a stasys field of some sort WHICH was still working when the Nostromo crew arrived there, just proving that the engineers really knew how to build their machines, THAT stasys field being what kept those bioweapons still viable after thousands of years (the last pilot knew the field would be functional and thus advised for no one, NEVER land on that moon (Movie's Director Cut and Book) No mistery there, just facts that were explained way back then both In the Movie and In the book XD XD Just that, which does answees the first post directly. Differences among the two depicted creatures are just because they ARE NOT the same thing, maybe the organism showed in Prometheus even possibly being the original life form whereas the ones on that cargo hold were the product made to be used as bioweapons...final adapted product based on that organism template. As a biowepon the smaller facehugger and the apparently more armored organims shown in Alien could be more effective as bioweapons, with even some enhancements into aggressivity and and possibly intelligence.

Cypher answered the question about "How the Alien was alive for so long". None of us really know why the Squid, that came out of Shaw, was different to the original facehuggers but the best guess would be that Ridley wanted something different to the original creatures, if they would have made it more like ALIEN, then the squid would have been more like the original facehugger. It's basically just a facehugger remake, which, most people find hard to accept because they love the original facehugger, including myself. The way i explain the difference of the deacon to the "xeno" (apart from Ridley wanting something new) is that the deacon looked the way it did because it gestated inside an engineer. The engineers are much bigger than us humans and apparently, they are purer than humans which is why the deacon looked like a purer version of the original alien (necronom) LOL. Also, during the scene where the deacon rips its way out of the engineer, the giant facehugger (squid) looks dead, just like the original facehuggers after they have released their seed.

Kind of, as it is not said the thing could still be viable for thousands upon thousands of years... Best and probably the real thing ( as shown in the first movie and book alike) is that they were kept viable due being inside the stasys field in the juggernaut class ship we saw in the first movie. It was clearly a good attention to detail back then and it is a good story telling attention, as making them so durable is a bit going over the top...and something not necessary, as well as giving too mueh to the creature, which is in the end just a very sofisticated bioweapon since thr first movie years back, no matter what the fans of that organism might say. I am nowhere a fan of that thing, being a fan of the science fiction context behind it, so it is easier for me I think to see it that way. Lets see what comes ahead, but I would really like to see the whole concept back to what it was in 1979 for the creature, and bring it to its real size, a bioweapon that can even have an easy turn-off trigger developed by the ones who created it. With a tech millions of years old that is something we should expect...

@Void, In the book, Ash also describes the Space Jockey as belonging to race of " noble people........." Which was the feeling I got from him when I first laid eyes on him. I never thought the species was at all sinister, just in the wrong place at the wrong time. And look how that ended up?

Yeah, I remember Ash comment on them, after telling Ripley the real content of the message. I had the feeling back then that there was more in the message, but even the book has little on that, although a lot more than in the movie. I remember first being impresed by the aesthetics of the ship, then the alien corpse (something missing in the book, as they never found any body inside the derelict in the book) and the feeling of an old tragedy... I read the book after watching the movie so the movie itself was able to convey the idea... And even noble races could be engaged in a war against a terrible foe, needing weapons like the one we see in the movie, although such weapon would be clean. I take it the design should call for a very short lifespam. Once no more hosts were found it would spent itself. A noble weapon of sorts if you think about it...

[b][i]"None of us really know why the Squid, that came out of Shaw, was different to the original facehuggers"[/i][/b] Well i have a theory but back to that later. First of all though Ridley wanted to leave some hint that connects the Xeno to the Engineer and he did that via the Substance in the Urns and how they mutated the life forms it comes into contact with to carry Xeno DNA The Squid was the one that would have the most DNA of a Xeno and less of Host Organism because of this process. The Urns Black Goo mutates any organism DNA it comes into contact with so that they maintain some of their original DNA/Traits and also Xeno DNA/Traits, if the process was to mutate them all into Xenos then why does the Worm maintain a part of its look and traits (regrow head) and why did Fifield and Shaws Baby all not look like the Hammerpede. The stuff basically re-writes some of the Organisms DNA so we can assume that if we took a Fish, a Cat, a Bird and a Human and dunked them into the Black Stuff they would not look the same but if we dunk two same kinds of Cat they would turn out similar.. hence the two Worms became the two Hammerpedes. The end result was to show that via this substance and more likely because a Embryo has not full formed into a Adult and thus has less none Xeno DNA to re-write thats how we get to the Squid Baby that is closest to the Face Hugger and any Organism from the Xeno Life Cycle simply because a Embryo is the base stage for all life and thus less DNA to re-write. Also the Original Star Beast Script had the Face Huggers described as Octopus like and i think Ridley wanted to use that concept for Shaws Baby, so Shaws Baby was how the original scripts Face Huggers looked. But the end product Chest Buster from that script looks nothing like the Xeno or Deacon.

[i]"None of us really know why the Squid, that came out of Shaw, was different to the original facehuggers but the best guess would be that Ridley wanted something different to the original creatures"[/i] Someone posted some links a while ago showing that the adult squid / trilobite, whatever it's called, was heavily inspired by a cartoon strip created by French artist Moebius. Sorry, can't find the article in question, but there is no doubt that's where the concept for the creature came from.