As we all know the Earth is flat. Once upon a time a group of explorers set off with the idea of proving that the world was round and that there was a route to the spice islands the other way, but the few survivors came back screaming about seeing ships falling off the edge of the world and something about dragons.
- Some sort of "universal down" keeps everything on the top of the planet.
- Anything underneath falls away (no turtles this time).
- We're not sure how the atmosphere stays in place.
- The Earth's crust varies between 5km (Oceanic) and 50km (Continental) thick.
- The planet runs from Pacific to Atlantic, no Americas, no Antarctic, no Antipodes (sorry Cobbers).
The world's water levels seem to run down slowly but every 12 hours or so they're topped back up again. Nobody knows how this works or where the water comes from, apparently arrangements are made. What this means is that that there's an apparent infinite supply of water and the edge of the world consists of a constant waterfall.
How long would such a planet continue to exist if subjected to normal erosion from said rimfall?