The oldest extant written Chinese music is "Youlan" (幽蘭) or the Solitary Orchid, composed during the 6th or 7th century, but has also been attributed to Confucius.

The answer is: it depends on the language. For Mandarin Chinese, especially in modern pop music, the melody usually takes over and the four lexical tones are ignored. Native Mandarin speakers will still be able to understand the meaning of the song by the pronunciation of the words even without the tonal information.