Possible major science flub in Promethius: that our DNA is 100% identical to the engineers' DNA. How could we have the same code? Obviously the film shows some kind of panspermia in the opening scene. I'll try to provide a couple plausible scenarios that the film is trying to present:
1) Panspermia happened billions of years ago and explains the abiogenesis of self replicating molecules, after which evolution did its thing as recorded in our real life biology. Maybe this explains, in this Alien fiction, the Cambrian Explosion. The problem here is that our genetics as they really are, the product of evolution, would not end up the same as the Engineers' genetics that we (and all terrestrial life in this scenario) was evolved from. So the only way around this problem is:
2) Panspermia happened much more recently, maybe half a million years ago--very late in the evolution of terrestrial life, which was actually just the creation of the human race on earth. This scenario fails because we share a relatively recent common ancestor with the other great apes, as our DNA shows. So then you can say, maybe the point of intervention was the common ancestor with great apes itself. This fails because it defeats the 100% identical claim, as we don't have that close a match with our ape brethren, let alone with the common ancestor.
Am I missing something that the film was trying to imply?
Anyway, just thought I'd toss it out there. Scenario #1 would have been (more) acceptable if they had claimed the Engineers had a four protein based replicator exactly of the same type as all life on earth. But they just HAD to say it was identical to ours...