Pinpointing the exact start of rock and roll is tricky, as it was a fusion of several genres that evolved over time. However, we can say that the roots of rock and roll were firmly planted in the 1940s and 1950s.

Here's a breakdown of key influences:

* Rhythm and Blues (R&B): This genre, with its strong backbeat and emphasis on vocals, was crucial. Artists like Louis Jordan, Roy Brown, and Wynonie Harris laid the groundwork.

* Country Music: With its focus on storytelling and simple melodies, country music contributed significantly. Think Hank Williams and Jimmie Rodgers.

* Gospel Music: Gospel music provided the energy and passionate vocals that rock and roll would inherit. Sister Rosetta Tharpe is often cited as a key figure.

* Early Rockabilly: A mix of country and R&B, rockabilly emerged in the 1950s, with Bill Haley & His Comets popularizing the genre. Their 1954 hit "Shake, Rattle and Roll" is often cited as a foundational rock and roll song.

A crucial turning point arrived in 1955 with the release of Elvis Presley's single "That's All Right." Elvis combined the energy of R&B, the storytelling of country, and the vocal power of gospel. This fusion, coupled with his charismatic stage presence, ignited the rock and roll explosion.

Therefore, while we can't point to a single date, the mid-1950s, specifically 1955 with Elvis Presley's emergence, mark a crucial turning point in the evolution of rock and roll.