Originally Posted by
bat39
So from what I understand, the basic idea is that everytime the history of the main DCU earth is altered, the previous history gets preserved as a parallel earth.
Let's call the main DCU earth "Earth 0" (it hasn't always been called that but let's roll with it).
Earth 0 was originally the Golden Age earth (with Superman showing up in 1938, the JSA etc.)
Earth 0's history was then altered to become the Silver Age earth AKA Earth 1. When this happened, the previous Golden Age history was preserved on a parallel earth that came to be known as Earth 2. This was basically the set-up we had from the start of the Silver Age up till COIE.
After COIE, Earth 0's history was altered again, and became a blend of the histories of Earths 2, 4, S and X. But the previous Silver Age history was preserved on a parallel earth that is now revealed to be Earth 1985.
Earth 0's history was eventually altered again post-Flashpoint as a result of Manhattan's tampering, becoming the New 52 earth. But due to the events of Superman Reborn, and now Doomsday Clock, that tampering was undone and Earth 0's history was mostly restored. However, as in previous cases, a new parallel earth has been created to preserve the New 52 history, called Earth 52.