My first recollections are of 1954 and a young DJ in NYC, Alan Freed, who is credited with coining the phrase "Rock and Roll"... his RnR show at the Brooklyn or Manhattan Paramount Theaters were legendary with 'Sam the Man' Taylor and his big band backing up the groups ...
http://www.alanfreed.com/ Freed played a lot of RnB and RnR recorded by black artists, whose songs were covered by the likes of The Crew Cuts, and Pat Boone !!! ...
Then came DJs like "Cousin Bruce" Morrow (who I believe is still around) and legendary Scott Muni and "Wolfman" Jack ...
One of the first songs I remember was The Penguins "Earth Angel" which was recorded in 1954... I had an original 78RPM recording which unfortunately got into the wrong hands and broken a few years back ... Then came groups such as The Platters, Frankie Lymon and the teenagers, etc.
I listened to Chuck Berry, Elvis (of course), Gene Vincent (BEE BOP A LULA) and a bunch of others ... It was a really happy time in my musical journey ...
It led to me starting a RnR band in high school which shortly thereafter transitioned into the group I was with for 26 years ...
As for it "building slowly or was it an explosion" ... it was DEFINITELY and explosion!!! ....
The "oldies" are STILL part of my repetiore ...
t.