This is a Sci-fi Movie, which means the fantasy part of it allows you to decided what ever the hell you want the ending and narrative to be, without having to back everything up with a clear scientific explanation. To those extreme negative reviewers, I appreciate you don't like the film and you feel it lacks emphasis (it does). However It would have to be a two part movie to fully explain how the whole planet got to be so inhabitable as well as giving you an idea of how life would continue again. Sometimes it better to not give the whole context away. Remember great Sci fi films give us the chance to use our own imagination or scientific knowledge to decided and conclude what’s happening on screen.