I made a community world on minecraft, before the 1.8.2 updates. It has amazingly flat land, and my friend didn't believe that I made it without creative mode, so we started grieving the world without saving, and we found 8 amazingly deep ravines and 5 mineshafts, and now he won't believe that I made it before the updates, is it possible for them to spawn after updates?
It would be easy to see if it was unexplored as you would get sudden chunk biome changes.
And mountains would be cut in half etc.