Gosh, do you think someone in the office dug out old copies of ALL-STAR COMICS to find likely springboards for a new Justice League story. Absolutely.
A lot of odd things come to mind looking at these covers. First, the last issue of ALL-STAR COMICS with the Justice Society, 57, had come out in 1951. Here was the shiny new Justice League less than a decade later. It wasn't as if there had been half a century between the titles. Of course, back then, editors figured a turnover in the readership every fix or six years. Without the Internet or convenient reprints or comic book shoppes, new readers only knew what they found in the issue right in front of them. As the Golden Age characters started to turn up in new comics, young fans were unreasonably excited. Here was their clue that an entire array of colorful heroes had once existed and were coming back. And they were different. Who was this creepy Spectre guy? Dr Fate? The Sandman? Green Lantern with a cape and blonde hair, the Flash wearing a metal cap like Mercury? What an unexpected thrill.
There was no Earth-One or Earth-One even as a concept in 1960. Superman, Batman and Wonder Woman had kept their own titles in unbroken publication all along. They were not new versions, they were the only versions. It wasn't mentioned, but there was no reason not to think this was the Superman from ACTION COMICS# 1, back in 1938. Actually, Aquaman had been appearing since 1941 as well, although as a back-up feature. J'Onn Jonzz, the Manhunter from Mars, was an all-new creation who had debuted in 1955, but he also had been kept in back-up status and had never even appeared on a cover before. It was the new Flash and Green Lantern who were the big sensations of the day. With streamlined new costumes and origins, they were not just dusted off Golden Age heroes but new idols suited for the Space Age. They were the Baby Boomer's own.