Bioweapons?

When the dvd comes out we can turn on the engineer subtitles or the engineer language track and finally see/hear what David said!

Munch on this. The liquid is shown as an organic aggressor substance. -The earthworms turn into arm breaking acid snakes -A wounded Fifield turns into a zombie (who is blind potentially(xeno-similarity-unconfirmed) -An infected Holloway (who may have turned zombie) impregnates Shaw with Cuddles (a facehugger relative) that puts a chestbursting xeno into the engineer at the end -Thus, we can assume the liquid is a life-destroying substance that in its natural cycle would produce the xeno (Alien) we are used to seeing. That xeno is the perfect predator and a colony of them would wipe out any population like a plague. -There are thousands of canisters that are non-organically made. This would insure quick and widespread infection to Earth through the soil. -So black xeno liquid of death + tons of engineer-made canisters (bombs) + ship heading to earth = bioweapons -The question is why they wanted to kill us all. Could be the 2000 year old Jesus theory, the Sumerian myth (human jealousy/hatrid theory), or they want our planet. Although I don't know how they would kill the xenos effectively. -We don't know exactly what killed them 2000 years ago. Most likely they were unable to contain the fluid/infection (pile of chest bursted engineer bodies), and one sealed himself in stasis. It would appear xenos killed them, and we are lead to believe xenos have a very short lifespan (a few days at most) so that is why they are no longer there. This moon was terraformed to act as a spaceship/military dock facility. You're right though. There are 5 ships total, and it seems no engineers have returned since. I don't think we have enough information to answer this yet. -We definitely don't know what David said. Could have been anything, but it obviously didn't please the engineer. Keep in mind he was just woken up from a 2000 year sleep, by humans (he was intent on eliminating), they are fighting and arguing with eachother, and an old one has shown up asking for immortality. We saw how difficult it was for the humans to awake from 2 year sleep. At least give him some coffee first! Sorry there's so much text but I hope you enjoy this answer!