The 2 genetic materials

In the urns we see 2 distinct types of genetic material - the black goo that later flows out over the floor when exposed to an oxygen rich environment (we can safely assume that when the door closed 2000 years ago to the urn room that a vacuum was created, hence the survival of the head). The oozing is undoubtedly deliberate, IF the urns were to be used as a "bomb" per se. Now, back to goo. The black goo ALONE we know causes mutations leading to violent characteristics in the host, and accelerated evolution. Take the worms and Fifield. The Goo within the vials that are surrounded by the black goo in the urns is entirely different. When it is unwittingly given to Holloway, he transforms - relatively slowly, but is devoid - seemingly - of aggression, and his transformation is not so horrific. And the third goo, rarely mentioned - the green slime David removed from one of the runes on the wall that triggers the hologram playback. It seems to definitely be biological too - maybe it is the second type of goo found within the vials. Maybe it is genetic spatter from the violent deaths of the exosuited Engineers... Snorkelbottom surmised the premise of the urn/goo/vial pretty well, but maybe not perfectly. As stated, if the black is ingested alone, it caused cellular breakdown, and then regeneration - the sacrificail Engineer, Fifield - and induces a malevolent character to the regenerated lifeform. The vial goo alone produces a worm-like infectious "parasite", that seems relatively benevolent, but when sexual reproduction occurs, produces a form of Xenomorph - after crossing "species" twice - Holloway to Shaw, Shaw births a Squid, the Squid fellates the Engineer, the Engineer gives birth the a Xeno. Yet, in my opinion, the Engineers are already hybridised with the Xeno with such strikingly similar anatomical features, so the offspring is???? Confusing is what it is. Can't do a Punnet Square on this lineage LOL. So, back to the goo, potentially as a weapon. I believe the Xeno-Engineer hybrids were a stepping stone in the evolution of a weapon - from Pure Engineer, to a hybrid Xeno-Engineer, to a full blown Xenomorph, that seemingly required a FEMALE to add the missing link for full evolution. Perhaps as Snorkelbottom suggested, there are NO female Engineers - they have been bred out, or sacrificed in order to create the Xeno-Engineers in the first place. Or who the heck knows! ;) It's just a movie, though one that REALLY fires the imagination. Scott has that uncanny ability to juxtapose and contradict... from a seemingly replication of Annunaki and Greek mythology to create the premise of the story, to doubting religion, to reinstating religion with the Who created them line, to.... The Chicken or the Egg is a good alternate title for Prometheus.