Life genesis scene -Scientific nonsense

The scene where the engineer sacrifices himself to seed life on earth doesn't make sense biologically. I am assuming that this is primordial earth since there is no vegetation, which means it;s happening 4.5 billion years ago. His DNA is cut in pieces which form the basis for whole life on earth. Humans appear 4.49 billion years later and have identical DNA to the engineers ! Well we don't have 100% the same DNA with our relatives how can we have the same DNA with the engineers who obviously look different? And how the DNA sequence was conserved through 4.49 billion years of evolution on earth? And all life on earth and its DNA is shaped by the earth's environment through natural selection. Of course, RS thinks that all Darwinism is nonsense and probably chooses to believe otherwise (like Shaw does). Maybe he would think different if he would have taken Biology 101 (but probably they wouldn't offer it at West Hartlepool College of Art). Also, by the way, DNA at the molecular level doesn't look like the rope ladders shown in the scene.