It's so interesting how Ridley changes. Remember this quote:
"If we're fortunate enough to make more 'Prometheus' films, you could make ten, and not link up with the Alien franchise, or you could do as Ridley's suggested and make two more," explained Michael Ellenberg, one of the executive producers on the film. "From the beginning, what Ridley was passionate about was not making a prequel that would tell you who Ellen Ripley's mom was, or how exactly that ship got there, that was never what he was interested in. He was interested in much larger questions about the nature of life itself, who we are, how we got here, and what he saw was a larger idea in the franchise that had never been explored: who would make such a horrible creature and why? And in looking at that creature, it came to look at the origins of ourselves."