What is the Prometheus movie about ?
The sacrificial engineer how long ago did the Engineer sacrifice himself?
Earth is about 4.5 billion years old now, and the Engineer at the end of the movie has been asleep for the last 2000 years, If we say that Earth at the beginning of the Prometheus movie is around a billion years old that gives us around 3.5 billion years of evolution for the engineers and the story. A lot can happen in that time. Can you imagine where the human race will be in 3.5 billion years time let alone a superior race like the engineers?
The question is why they want to mix their DNA with our planet. Is it ritual? Are they told to by their God or a race superior to them? This part of the story has been left to us to decide and therefore adds some mystery to the engineers!
Homosapiens 200,000 years old and 50,000 years ago showed civilized traits( there has been evidence come to light since writing this that the was minig on the earth 170,000 years ago in Africa, and that Africa was the bowl of human civilization.)