In what decade did rock and roll music first emerge?

ROCK 'N' ROLL. Through a series of interesting personalities and promotions, rock 'n' roll was invented in Cleveland in the early 1950s. In the late 1940s, LEO MINTZ, the owner of Record Rendezvous, saw the decrease in sales of big band records. Mintz, however, saw how his young customers would dance around his store when the manager played Rhythm & Blues (R&B) records. In order to eliminate the racial tone of this music from the deep south, he called it rock & roll. The term "rock 'n' roll" had been used since the early 1920s as a blues song lyric meaning sexual intercourse. Mintz tried to get airplay for R&B records, but the 6 radio stations in Cleveland played only music by white musicians.

Source: Britannica