- Xenomorph blood *doesnt* eat through glass. Alien blood oxidises and quickly becomes neutral, which is why both the dead and living facehuggers at Hadley's Hope were placed in water within glass tubes in medlab (in case of bleeding). Both Ripley and Newt's cryotubes confirm this in Alien 3 - visible cracks to glass, but burns only viable on the side metal. This tells us that helmets worn by the Nostromo and Prometheus crew are likely made from a very robust plastic (which makes sense - glass would be heavy when worn in gravity environments). And yes, I'm completely ignoring Ripley 8's blood.. Cause.. 'Resurrection' is poor fanfiction at best.
As for why the grappling gun doesn't melt when a Xenomorph was blasted out of the Narcissus airlock? It penetrated deep, and opened inside, sealing the wound from within - it probably was melting slowly within, though we have no *conclusive* evidence that Xeno blood 'burns' in a vacuum... The only time we *think* we saw it was the facehugger that melted Kanes helmet, though since Dallas, Lane and Lambert weren't carrying a lot of scientific equipment, it's entirely possible that the derelict had its own internal atmosphere just like the facility on LV-233 and they simply weren't aware.
On the subject of the Jockey: It was old.. Thousands of years old. David didn't create the xenomorph. David mimicked what the engineers had already done before him based on writing he found, though his was not the 'perfect organism'. David's creation was organic, and lacked a biomechanical exoskeleton. We see in Prometheus that the Engineers on LV-233 are augmented - the biomechanical exterior is part of their body, it is not a suit (the engineer that David awakes on the juggernaut from hypersleep is actually naked). They are different from those seen seeding life on Earth or like the people seen in Covenant.. So why is the XENO that bursts from Kane biomechanical? Simple:
In the derelict, Lambert asks "I wonder what happened to the rest of the crew". They find them.. Or rather Kane does. The eggs were morphed from engineers. Aliens take on genetic traits of hosts. Sooo... Biomechanical infused egg - human host = slightly diluted XENO (still has Biomechanical traits). This accounts for different exoskeletons in 'Aliens' - Russ Jordan pops a Biomechanical XENO, it eggmorphs a number on colonists.. So now it's derelict egg - human host - big chap - eggmorphed human - human host... Eventually a queen is born so same as above, then lays eggs - human host and repeat.. Diluting each time and mixing more human dna into the mix /less biomechical traits.. This is why the runner in alien 3 is completely organic. This is why David's creation is organic. A true XENO has the same Biomechanical traits as its engineer host creators.
How did the egg get on the sulaco?
-it wasn't Bishop (impossibility, eggs are sourced from sub level 3 of the atmosphere processor.. Exactly where Ripley was)
-it wasn't carried by the queen (we have Eyes, and can clearly see this)
-it wasn't an "emergency egg" (c'mon, we literally SEE undeveloped egg yolks pouring from within the egg sack when Ripley grenade launches it.. The eggs develop within the sack, not in the queen)
-nobody "put" it there.. A human would trigger it hatching and an android wouldn't position it upside down in the corner of a room
-it wasn't eggmorphed from Bishops legs (which, you know, were sucked into the vacuum of space).
-it wasn't a dream (that's just overused and lazy as f**k.. Plus Alien 3 is an underappreciated masterpiece).
Logical deduction: bundled with the fact we see the crew in, not only different shaped cryotubes, but a different cryochamber completely than what we see at end of Aliens (yes, I am well aware it was a directors choice, but we roll with what is seen), and the fact that the only way an egg (or cluster of eggs) could be positioned in such a fashion is by a XENO, the *only* logical choice is that there is a part of the story we have not seen yet, between Aliens and Alien 3. There is nothing in Alien 3 that would contradict such an event.. The nearest mention of past events is in the Assembly cut when Clemons tells Andrews that Ripley was part of a military operation that suffered losses (paraphrasing). That's it. Ripley also mentions to Clemons "I've been out here a long time" (of course, talking about her experience of Space in general, 57 years cryo, etc etc) but in the right context, it works.
