Yesterday at the bookstore I browsed through Avatar: An activist survival guide, and saw some screencaps depicting the future Earth. The idea is that by that time, Earth had become used up and was decaying. There's a pic of an overflowing dumpster to convey this. 

So, when I go see Avatar next month, I'l be there not only for the 3-D & hovering mountains, but to glimpse the mid-22nd Century.