The closest date to possible destruction of earth from a scientific standpoint that I have read of will take place in the year of 2880 or something to that extent.
Just out of curiosity, I was watching that movie "Deep Impact" and typed in E.L.E. to see what would come up on wikipedia. To my shock, I read that NASA is currently following an asteroid's course.
http://en.wikipedia.org/wiki/%2829075%29_1950_DA
Supposedly it will either just miss earth or definitely hit earth and kill most or all living things on earth. But we have a few hundred years to come up with a solution.
Here is another link that speaks of this asteroid and other near earht objects that can strike earth.
http://en.wikipedia.org/wiki/Near-Earth_object
No worries, we'll all be reincarnated many times over before this thing hits if it happens. Unless a black hole swallows our solar system first.