AS IF, FOR SURE

[Janis Vizier Nihart]

I'm looking for the origins or the earliest references to the expressions "as if" and "for sure".
I know they were part of the Valley Girl  lingo back in the eighties.  But I remember using both as a child growing up in the fifties on a small island off the Louisiana coast.  We didn't use the same rising inflection(or whatever -I'm not a linguist, but it does interest me).
We used both  "Anh, as if" and  "FOR SURE" (PRONOUNCED "FUH SHORE") to mean definitely not.  For sure would also be used as definitely yes.  If one said For Sure in a sarcastic tone, it meant "No".
I'm just wondering how an isolated community in the 1950's would be using terminology that is atrtributed to California girls in the 1980"s.
I hope someone can answer my question.   Thanks

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