1578
Sea Level
(imgs.xkcd.com)
Alt text: They're up there with coral islands, lightning, and caterpillars turning into butterflies.
If the Earth was scaled down to the size of a billiard ball, it would be the smoothest billiard ball in existence.
Except for Howie Mandel's head, of course.
I'll take your word for it, because it would be awfully hard to compare it to other billiard balls after we'd asphyxiated from the atmosphere dissipating into space.