Yes, the roots of modern hip-hop are in the 1970s in Brooklyn, with a merging between the sound system culture brought to New York by Jamaican immigrants and various parts of funk/soul (e.g., b-boy moves apparently originally coming from James Brown's stage moves).

1970s hip-hop was basically dance party music, with DJs who occasionally rapped over the music they played. To modern ears it would sound more like an hour-long DJ mix with occasional bits where someone rapped over the top as opposed to a coherent 3-minute pop single.

According to Jeff Chang's book Can't Stop Won't Stop, the Sugar Hill record label owner Sylvia Robinson saw the popularity of the music played at these parties, and tried to sign up the (very popular on the scene) likes of Grandmaster Flash and the Furious Five to her label; Grandmaster Flash refused, believing the music would not work in shortened form. In the end, Robinson gathered together some no-name guys from the hip-hop community who at many points were using other people's rhymes, and dubbed them the Sugar Hill Gang. Robinson got them in the studio rapping over a band doing a version of Chic's 'Good Times', called it 'Rapper's Delight', released it in August 1979 and had a worldwide hit.

Chang also mentions 'King Tim III (Personality Jock)', a song by the Brooklyn funk band the Fatback Band that was released as a b-side to another song in March 1979. The Fatback Band were a long established funk group who'd been around for a decade, and according to a November 1979 Billboard article, the group's keyboardist/producer Jerry Thomas had heard a tape where a rapper did his thing over a Roy Ayers instrumental. Fascinated, he located the rapper - Tim Washington, who rapped under the name 'King Tim III' - and got him to rap over a Fatback Band track. When 'Rapper's Delight' started to take off, the Fatback Band's record label realised what they had, and promoted 'King Tim III (Personality Jock)' as a single, and 'King Tim III' went up the soul and disco charts piggybacking off the success of 'Rapper's Delight'. So 'King Tim III' was recorded before 'Rapper's Delight', but the majority of people at the time would have heard 'Rapper's Delight' first.

Outside of the specific Brooklyn scene that birthed modern hip-hop, there are a variety of pre-1979 songs that could be called 'rap', in the sense that they involve people somewhat rhythmically but non-melodically exclaiming over music, from Bo Diddley's 1959 'Say Man' to Bob Dylan's 1965 'Subterranean Homesick Blues' to Gil Scott-Heron's (notably closer sounding to modern rap) 1970's 'The Revolution Will Not Be Televised'.

I suspect that 'The Revolution Will Not Be Televised' will sound like hip-hop to a casual modern listener - it's certainly been widely sampled by hip-hop artists. But it isn't quite hip-hop. Any genre, including hip-hop, is usually a manifestation of a particular subculture, with a set of rules both musical and cultural. 'King Tim III' and 'Rapper's Delight' are recognisably related to Brooklyn hip-hop culture in a way that Gil Scott-Heron is not. I couldn't imagine Scott-Heron dancing b-boy moves or tagging graffiti, for example, but I can definitely imagine Big Bank Hank of the Sugar Hill Gang or King Tim III doing that.

(edited for more detail and context)

Hi, it may be worth x-posting this question to /r/hiphopheads