I'm getting to that. Okay, so the world get to a point where it has evolved as much as it can. We, and everything else, have reached a peak and the only place left for us to go is back down. This is the point on the circle of time that is exactly opposite the point were we started. We start to de-evolve.
Time becomes sort of a twisted mirror image of the other half of the circle.
Eventually, Earth is like it was before Humans, and slowly it becomes like it was when it was young, except now it is old. Then it is gone. And then everything is gone. Things are now back to the way they were when Bob first came out of the Nothing. And we are back where we started.