Obviously the further out you go, the harder it becomes to forecast. So the (very) long-term stuff is mainly just sci-fi and wild speculation.
However, a lot of these predictions aren't just guesses, but are actually "scheduled" to happen, e.g. solar eclipses, the return of Halley's comet, and geological events.
Ultimately though, the timeline is just a bit of fun, to get people thinking about the future. Although it deals with important issues, you shouldn't take it too seriously.
Personally, I'm trying to focus on living in the present, and enjoying the here and now. The future will take care of itself.