First before reading this see Hawkdeath's post named "Origin of the Flash Sideways Timeline" he has some very solid theories and it looks to be a popular post so i would like to continue it here, but with a smal, yet possibly large, tweak.
Proposing that the meeting with the others in 1954 is the earliest event is incorrect.
For this discussion please regard the very popular thought that it was Sawyer holding onto the rope at the site of thw well hich caused the well to be dug.
Allowing this we need to see that this would be the earliest event changing, and that possibly POSSIBLY mind you, the well never being dug could have caused some core values of the islands dynamic. It could be that this shift so early (possibly) in the islands history and not the bomb in 77 which led somehow to the sinking of the island and the entire FST.
I apologize but i do not know how to link to his post.