A few funny things regarding dating this "exact duplicate" of Earth... Spock is making a series of very dodgy assumptions there.
At beam-down, after a brief debate, our heroes agree that the place looks like 1960s Earth, as opposed to "the early 1900s" - and they base this on observing a street littered with 1940s and early 1950s automobiles and lined with buildings from no later than the 1930s in construction style! No TV sets or other modern amenities for sale at the windows, either. No street ads of 1960s style. Does Spock insert a correction factor and assume that a little town like this would always be 20 years behind the times?
Soon thereafter, Spock identifies a grand piano as being 300 years old. Apparently, said piano was brand new when disaster struck, as the records on the longevity project later prove that things went haywire exactly 300 years ago. Why the coincidence? Nothing else in that apartment looks brand new for the 1960s. Or even for the 1940s, for that matter. And more generally, the interior with its period-unspecific paintings on the wall is not indicative of a taste for modernity for the occupant, regardless of exact Earth analogies for individual items.
...Okay, so we do see the roller skate on the piano. Spock was probably giving his estimate on that, rather than the piano, then. But there's nothing about the design of the skate that screams 1960s (as that particular style existed since about 1900). And in any case, how can Spock tell how old these things are? He isn't using his tricorder, and it doesn't really make sense that he could divine their age by their design - a pseudo-1960s or a pseudo-1900s design could be two years old, or two thousand, for the degree of decay witnessed by Mk I Eyeball.
Later episodes suggest Spock is fairly ignorant about Earth history in general. Perhaps he's just bluffing his way through the mission, and Kirk hasn't yet learned to distrust his friend?
Timo Saloniemi
