It was 44 years ago that...


Parlaphone released the Beatles 'Sgt. Pepper's Lonely Hearts Club Band'.
What other albums can be considered having as much impact, actually altering the direction of a music genre?
montejay
Miles Davis did it twice with "Kind of Blue" introducing modal jazz, then "In a silent Way" introducing electric Jazz.

Miles basically invented jazz fusion, which open the door for all those groups that came after like Johnny Mac, Mahavishu, Return to Forever, Weather Report, Brand X... JLP.

So Miles really heavily influenced Rock and Jazz.. from Hendrix to Maynard F.
The Doors(st)album has influenced alternative music from the late 70's thru the 80's. It even influenced grunge 20+ years after it's release.
Since someone eventually got around to Pet Sounds, I'll add a single (rather than an LP):

Chuck Berry's 1955 release, "Maybellene", at which time - it could be argued - Rock n Roll is born.

Marty
One could also argue that Little Richard's "Tutti Frutti" released in 1955 impacted rock and roll much more.

Little Richard began recording in 1951, 4 years earlier than Berry.

He is widely recognized as the performer who transitioned rhythm and blues to rock and roll.