Help me with Black Goo

The 'black goo' can either create life or destroy it. In the beginning it was used to create life on earth, then the Engineers were planning to come back to use it as a virus to destroy it. How it chooses to do that I'm not entirely sure. I believe its used to breed the xenomorph in some strange way and that's what they were going to use to kill off Earth in the end. It reacts to environment change. The worms probably absorbed it and had their DNA altered rather then ingesting it..for all we know it could have killed them before mutating them...just like Holloway was dead before he came back in that crazy way.

The bioformer which decomposes life is contained within the VIALS INSIDE THE URNS. It is categorically not the mutagen that changes the worms/Fifield. Unfortunately they are both black and gooey. This point was glanced over in the film, but seems fundamental to it being more than a convenient plot device.

I think Its the same substance, the difference being that fifield did a face plant into the puddle of goo and Halloway/Engineer ingested it. Ingesting it would be the quickest (besides breathing) way for it get into your blood stream and spread everywhere. My theory is that its supposed to get into your bloodstream, cause body wide necrosis and then transform the dead cells into a virus that can rewrite DNA.

Oh yeah! You're right. David dosed him with the goo inside the vials which were inside the urns. And the Mohawk guy face planted into the black goo which was oozing out of the urns, but not the vials.

All of these explanations sound reasonable. Another thing I thought while watching was that it reacted differently based on what it infected. It dissolves adults in large doses, and dissolves them more slowly while causing severe mutation and possibly exploding heads in smaller doses. It simply mutates larval lifeforms, however, into some variant of a facehugger, the larval stage of the xenomorph life cycle. The two things we witness it mutate are mealworms, the larval stage of a beetle, and Holloway's sperm, the closest thing to a "larval" stage in a human (though technically a gamete). Then again, the gamete stage of a xenomorph would be the egg itself, which kind of is what Shaw gave birth to, not a full-fledged facehugger. And the infected adults seem to take on adult xenomorph traits, like the uncontrollable desire to kill, joints that articulate in many directions, and greatly enhanced leaping ability, while dissolving. Then again, it seems unlikely the goo has its origins in xenomorph biology, given that we witnessed it being used 3.5 billion years ago. I can buy that the engineers would undergo no physical-morphological evolution in that span since they seem to either be clones, engineered themselves, or simply very strict controllers of their own genes, but the xenomorphs wouldn't stay the same, given what we already know of them. The original goo from the beginning scene was probably just some enzyme they engineered to isolate and split DNA while dissolving everything else organic, apparently catalyzed by water, while in the interim eons they created different mutagenic forms of it and perhaps weaponized it by incorporating xenomorph DNA. Or it could just be an inert substrate that carries other substances that can do many different things.

Maybe the stuff that the SJ at the start of the film wasn't the same 'black goo' but rather a base biochemical substance capable of unzipping DNA and either creating RNA or simply more DNA. As we see in the film, when ingested the SJ's body is broken down into a "black goo" like substance which we then see is unzipped DNA. Rather than be caught in ampules it is instead dispersed into Earth's water system to later recombine and become the developing cells we see splitting. Perhaps the 'black goo' on LV-223 is simply the broken down DNA of an original Xenomorph species which they recognised as the perfect killing machine and thus both 'worshipped' (as with the Predator race) and used as a bioweapon. We already know that the Xenomorphs are capable of combining their DNA with that of the Host so perhaps this is another reason they chose them or why the 'black goo' is particularly invasive. The black goo in it's current form could also simply be a xeno DNA based mutagen formed from the original Bioformer that seeded Earth. The worms could have mutated and/or reproduced into cobra like things. The two guys affected by it could have been mutating hence his crazy crab walk. Elizabeth's 'baby' could have been a xeno mutant baby OR it could have mutated somthing else inside her such as a Virus/Cell etc which then infected the SJ at the end.

A good - but not perfect - analogy to the goo, for those of you who play video games, is the FEV virus from the Fallout series. It causes rapid changes on the genetic level, forcing the creature to rapidly evolve. In fact, there are creatures similar to the mutated worms seen in the movie in the game. It seems like the Engineers have some strains down path while others are more volatile. For example, the strand used to seed planets appears stable, but weaponized versions are not. Thus the die-off of the Engineer installation. Overall, it appears though to have a similar effect as FEV in Fallout. The exposed become faster and stronger than before (however, unlike Fallout, the exposed are not made sterile). If he had not been killed, would Holloway have become a berserker like Fefield? Did infected, mutant Engineers kill the installation? Was the decapitated Engineer a mutant (did the others close the door to seal him away?).