This was taken from a comment I saw on another site, and I did a little research and everything seems to check out! :
To give some historical/mythological background that may shed some light, Ridley stated the SJ culture was based on Persian Myths. This would be Sumerian/Akkadian/Hindu. This is all taken from the Atra Hasis.
Creators - "G"ods- Annunaki - Dragon Humanoids (Naga, Dragon Kings,)
Helpers - "g"ods - Igigi - Engineers. (Android like living beings....BIOmechanical humanoid. Key features- Pale skin and large black eyes. Also known as watchers, Grigori, and Archons) (in many summerian texts they are actually referred to as "Pilots". Pretty much the Annunaki Air Force.)
When the Annunaki began terraforming the earth, they had the Igigi do the work for them. After a few thousand years the Igigi revolted and went on strike. The Annunaki then decided to create humans to do the work for them.
They sacrificed one of the rebel Igigi named Geshtu to use his blood and dna to make human beings, by mixing it with elements native to the earth.
(In the movie, this can be explained by the the different oval spaceship at the beginning representing the spaceship of the Annunaki)
(It can also be explained by the concept art that leaked from the official book this week)....
So lots of mythology wrapped up in science fiction. Wonder how much of this will be expounded upon in the sequel..
Hmmm...It's already the highest grossing Aliens movie ever. It made $100 million in 13 days, and $227 million worldwide..budget: $130 million.
If the plot really is as convoluted as I linked above, it's kind of amazing the movie did this well...