TOS had the concept of parallel planetary evolution, which the rest of Trek (outside of William Shatner's novels with J+G Reeves-Stevens which made the multiverse the Preservers' petri dish) has mostly ignored. We visited worlds in the 1960's, in a bizarro modern Rome and planets almost geologically identical to our Earth.
But who's to say Star Trek's Earth is the original? Or that Star Trek's Earth is "our" one, and not a duplicate 10,000 light years away and 300 years more advanced? Imagine if Star Trek came across a duplicate Earth 300 years more advanced with a Federation of it's own. Imagine being on Earth and learning your world is just some random copy.
Such an awesome concept.
But who's to say Star Trek's Earth is the original? Or that Star Trek's Earth is "our" one, and not a duplicate 10,000 light years away and 300 years more advanced? Imagine if Star Trek came across a duplicate Earth 300 years more advanced with a Federation of it's own. Imagine being on Earth and learning your world is just some random copy.
Such an awesome concept.