@SM and @whiterabbit, I admit this was wild speculation on my part...and I have no evidence to support my claims lol and in fact, it could be more like POMPEII, who knows at this point...
@BishopShouldGo, that's the fun part of participating in forums like these: speculation and theories.
"Das Rheingold, to outline it very briefly, sees a dwarf named Alberich steal a magical gold ring from a bunch of maidens who live in the Rhine. That ring, which gives its wearer power over the whole world, is in turn stolen from the dwarf by Wotan, a Zeus-like god of gods. Meanwhile, there's trouble in Valhalla: the gods have contracted a pair of giants to build them a luxurious new house, but when it comes time for the gods to pay up, they renege on the deal. What follows is an almighty tussle between giants, gods and ordinary mortals, with the purloined ring the MacGuffin at the centre of it all."@Ingwar, interesting reading...so, the black goo could be as an equivalent of the ring of Das Rheingold, an item that contains the power of the gods. And we have the mortals (humans), the Giants (Engineers) and maybe the Gods (those who created them). I think a great battle or event occurred in the ancient past...and I wonder if we can see part of this conflict at the present time (Maybe David will unleash hell in paradise). Also, Engineers can be divided into fractions:
a) Those who support God
b) Those who support Satan
For a civil war I can think of several reasons, such as:
1) Space Jesús: There are engineers who want to help the human race to evolve...but there are evil giants who are jealous of the progress of mandkind, ready to exterminate life on planet Earth.
2) Prometheus Myth: There are Engineers who want to give powerfull gifts to mandkind against the will of God...
3) The rebellion of angels: Perhaps there are Engineers who want to be like their Gods (the original Space Jockeys), and they have stolen technology from them...perhaps they betrayed them and killed them.
4) Engineers have an enemy (Another race of aliens): unlikely, but this could explain why they have created a biological weapon so powerful and dangerous...
And that's all I can think of for now