Season 1 episode 8 (IMDB), episode 9 (Paramount), or episode 11 (Memory Alpha). Anyway, we get a complete copy of Earth, the failed longevity experiment, bonk bonk, and Kirk wrenching a kid off a desktop. Beyond that, no explanation surrounding AN EXACT COPY OF EARTH! Zero, zip, zilch, nada.
Side query: What’s considered the “official” episode breakdown?
If you’ve never seen TAS, you should check that out too, it gets even wilder with that stuff. There’s an episode that leaves a 50’ tall clone of Spock just kicking around the galaxy, and another episode where the crew meets actual Satan and he turns out to be a pretty nice guy.
Yeah, been meaning to delve into that, but have yet to acquire the hallucinogens necessary to do so.
It’s worth watching through once, just to check that box. It’s definitely a product of its time, and as little animation budget as humanly possible