About the time line.
It is safe to say that the time line was already an altered one given the evidence at hand. The Kelvin. The ship design was TMP (Trek Movie Picture)era although it was being used in pre-TOS (Trek Original Series) era. Look at the design of the Kelvin and you can see that it does not resemble in any way the Enterprise of TOS era, or prior. It however does resemble the Enterprise of TMP, post TOS era.
So it is safe to conclude that both Spock and Nero were products of an already previously altered reality prior to entering into the time line of he movie thereby altering that already altered time line.
I believe the time line was altered by the events that transpired in the TV series Enterprise.
Now I foresee the final movie in this new Trek franchise having Kirk return to the time proceeding Enterprise, and preventing the time altering events which caused the first alternate reality, his fathers reality, and eventually the altered reality that came about as a result of Nero's involvement.
Remember, in the original TOS, Kirk met the Romulans as a result of there aggression in the events of Balance of Terror some 100 years after the Earth Romulan war which NEVER took place in the era of Enterprise which is should have.* Additionally, Kirks family were killed by Governor Kodos, and Kirk had an older brother. The Enterprise was built in the San Francisco fleet yards, not in the corn fields of Iowa.
* A note on this topic. I would be safe to conclude that by the time the events of Enterprise had transpired, Earths history had already been altered by the events of First Contact whereupon the Borg had traveled back in time and attacked Earth thus altering the time line. However the time line was resorted by the efforts of Picard and crew thus this could not have been the event that changed the time line prior to Archers adventures.
Therefore the safe bet is to conclude that the events of the Temporal cold war were to blame for the altering of the time line that placed George Kirk on the bridge of the Kelvin at the moment that Nero entered into his reality.
Needless to say something altered Earths history prior to the events of Enterprise. Generally speaking by the time those events should have transpired, the Earth Romulan war should have already happened. And Zefram Cochrane should have been on the Alpha Centauri colony. (As noted in TOS Episode that featured him.)
Thusly something, or most likely someone, altered Earths history thus starting an alternate reality.
In conclusion it can be argued quite effectively that the Spock that went back in time with Nero was not the Spock from TOS or TMP era.
