Is the black goo really a weapon?

The Engineer at the end was certainly on his way to Earth, because the star map showed a growing green line headed for our planet as he was preparing to leave. I suppose you could twist the story round all kinds of ways if you wanted. For example, maybe the black goo behaves quite differently (for beneficial purposes) in Earth's environment. Given that the Engineers we've seen so far are probably part of a much bigger picture, who knows!

Bjorn: Welcome! Shaw and Janek took Earths destruction for granted under the stress of the situation and the information at hand. However, even if our destruction was the intent, it may not have been out of hostility, but rather necessity to the Engineers schemes. For example, they may have wished to evolve us into more of them. Is it possible Shaw killed the last surviving Engineer, or one of the few? If so, she's on her way to meet something much worse. The true purpose of the domes is unknown. LV223 was possibly just a remote storage location for the Goo ( I wish it had a better name ), which in and of itself is not a weapon, much like atomic energy. I'm stating all this from my own perspective, of course.

If worm from earth turned into say that creature. so that liquid, looks more like some steroid. Let's not think much on Lindeolf's imagination.

@Major Noob Yeah, nobody talks about the domes enough. The dome, mural, ceremonial statues point to religious characteristic of the location. The Engineers take this procreation thing very seriously. Or like many twisted religion, they could be fooled into maintaining self-destructive rituals that wipe out their numbers. The statue seems to reference the Easter Island giant face statues. If you Google the Rapa Nui people and their own extinction, you may get the rough idea of what happened on LV 223. Or is it? Like that pictogram on cave wall, the movie is incomplete and way too open for interpretations.

I believe that the Black Goo in the Urns could indeed be a Bio Weapon, but it would be a very peculiar one. You see from what i have seen these Urns are as ampules and they contain this substance and it appears that this substance when it comes into interaction with a Organism it does not kill the Organism, it upgrades them both physically and mentally. By that it mutates the Organisms Genes so that it takes on traits of a Xeno and thus changes the Organism into a Hybrid Organism that has Xeno traits but also evolves and improves certain aspects/traits of the original Organism. The level of this mutation depends on the amount of black goo the organism comes into contact with and how it comes into contact with it. My reasons for this are... we do not see what becomes of Holloway we can only assume, and so we get no proof that he was having the same affect as the Sacrificial Engineer. We do see that Holloway gets Shaw Pregnant while he is infected with a small amount of the black substance, we can only assume that the substance first affected his genes slowly but enough to affect and mutate his sperm. His Sperm then was able to fertilize Shaws none defective Eggs. The Embryo being a simple form of life (all mammals, reptiles, birds and fish have a similar near identical stage 1 embryo) Thus this embryo only has basic mammal genetics and thus has less Human DNA to rewrite. Thats how the Embryo mutated into the Squid which is very similar to the Face Hugger. Its assumed that those worms we saw that could have been brought in from outside by the crew; mutated into the Hammerpede which again mutated the worms into larger organisms that carried again some Xeno traits but also kept some worm traits. Next we have Fifield, now he gets a lot of Black Goo on his face... but forget the Fifield we saw... look at the many concept works only a few looked like Toxic Avenger Fifield, the others looked more Alien, you could see Xeno DNA in them but none in mutant Fifield. Why? Well if Ridley wanted to save the Xeno DNA until the Shaws Baby vs Engineer and then Face Hug (Body Hug) Scene and resulting Deacon Chest Buster. Maybe thats a good enough reason for him to cut out the Alien DNA looking Fifield and go with more bland mutant Toxic Avenger Fifield. Maybe the same as we really never see much of the Hammerpede or what becomes of its victims. Again purely on my part i think it was to edit and leave out Alien DNA until the Shaw Baby and its attack and implanting of Embryo in the Engineer scenes. So if we consider that Fifield was originally going to look more Xeno DNA than Elephant man (Joseph Merrick). I have come to this conclusion. The Xeno was a Organism that they may had used as a Bio Weapon, its use was simple, deploy the Xeno Eggs and watch as they hatch Face Huggers who then implant Xeno Embryo on its targets, these Embryos grown into Chest Busters who then grow into Xenos which take on some traits of its Host. The Xeno is deadly and also a very hard Bio Weapon to contain and control. What if the Engineers then found a way to use the Xeno well change it to something that can still be used as a Bio Weapon but one that can be contained and stored more easy. Surely breaking down the Xeno DNA and storing them in Urns are a much easier and safer way to contain and store a Bio Weapon? But how do they do that? This brings me back to the Sacrificial Engineer, the substance he had taken did not mutated him it broke down his DNA but did so in a way that his DNA then diluted into water and may had then either mutated into basic life forms and building blocks of life on Earth.... or maybe mutated basic life forms on Earth so they evolve into Organisms that carried some DNA and traits of the Engineer Race. I propose that the Goo the Engineer drank was not the same as what was in the Urns. I believe that they used the same process that broke down the Sacrificial Engineers DNA to break down the Xenos DNA, but where as the Engineers DNA escaped into the Water Fall, the Xenos was collected into the Urns and maybe also mixed with some other chemical that helps to store and hibernate the DNA and maybe helps it Evolve and Mutate at a quicker cycle of Evolution than that of the Engineers DNA.. Unless the Xenos DNA mutated and evolves at a much faster rate anyway (likely). This is what i feel the Black Goo is.... broken down Xeno DNA for a safer way to store and deploy the Xeno Bio Weapon and also have more varied use. Maybe they never created the Xeno, but they came across it and wished to use its DNA to be used as a Weapon or to create new Organisms with Xeno traits. I also think this is what the Space Jockey Suits are, they are Bio Suits, whose purpose it to prevent contamination of the Black Goo and maybe protect them from the Black Goo but not any accidentally created organisms via the Goo. Remember the Urns only appeared to activate and leak once some of the crew had taken of their helmets and their breathing affected the atmosphere of the room and caused the Urns to leak. This is why the Engineers wear those suits.... as they could breath outside for at least a short period with them off (The Engineer got from his crashes Juggernaut to the Lifeboat to attack Shaw without a mask). Also why wear those suits in the Ghost Engineer scene, when the Human Crew could walk around without them as there was oxygen in that part of the temple and the Juggernaut.