Wikipedia
Earth-One (also Earth-1) is a name given to two fictional universes (The Pre-Crisis and Post-Crisis versions of the same universe) that have appeared in American comic book stories published by DC Comics. The first Earth-One was given its name in Justice League of America #21 (August 1963), after The Flash #123 (September 1961) explained how Golden Age ( Earth-Two) versions of characters such as the Flash ( Jay Garrick) could appear in stories with their Silver Age counterparts (Barry Allen). This Earth-One continuity included the DC Silver Age heroes, including the Justice League of America. Earth-One, along with the four other surviving Earths of the DC Multiverse, are merged into one in the 1985 miniseries Crisis on Infinite Earths. This Earth's versions of characters were primarily the Earth-One versions (i.e. Superman, Batman), but some characters from the four other worlds were also "folded" in. In Infinite Crisis, Earth-One was resurrected and merged with the primary Earth of the publication era to create a New Earth that brought back more aspects of Earth-One's original history. In 2007, a new version of Earth-One was created in the aftermath of events that occurred within the '' 52'' series.