Black Goo & Sacrificial Goo

One question that I have which is based on an assumption that a lot of people seem to have made - how do we know that the black goo from the urns and the drink that the Engineer consumed at the beginning are the same thing. Janek made an assumption that the complex on the moon was a base to create weapons of mass destruction. The worms appeared to advance in their evolutionary state. Holloway was going through changes which we were unable to see the end result. He could have been evolving into something close to an Engineer...... The only thing that makes me question this is Fifield. All we see is him fall after getting burnt by the acid from the cobrahugger and fall to the floor. Perhaps he is evolving but has brain damage from his injuries; thus explaining him attacking other crew members. I do not believe that the black goo from the complex and the substance drank by the Engineer in the beginning sequence is the same.... I'm hoping the cobrahugger gets a better explanation in a sequel or directors cut. The Engineers all look to be A sexual. The pile of Engineers all had holes in their chests. This would explain how the Engineer in the original Alien was fossilised after escaping whatever happened on the moon (but infected). Perhaps the cobrahugger develops / evolves into a facehugger?? Be good to know if anyone has similar views.........