http://breezewiki.catsarchywsyuss6jdxlypsw5dc7owd5u5tr6bujxb7o6xw2hipqehyd.onion/minecraft/wiki/Java_Edition_removed_features
Before inf-20100327 Terrain generation was much simpler in versions before March 27, 2010. While in modern versions, the noise generator used for terrain is 3D, earlier versions used a purely 2D noise generator for the world instead. The resulting terrain was much more cliff-based as a result, and overhangs were an impossibility.