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?
The only bit refuting that is the brief discussion about sending teachers and, according to Bones, “truant officers” to the planet after they leave. But then, all of that could be attributed to Kirk’s exaggerations.