As it happens, we have some surviving notated ancient music. Which means we can play it.
The ancient Greeks created a tuning system that was the direct ancestor of our major scale. Their idea was to use a sequence of perfect fifths that wrap around at the octave boundary. This idea was so successful that we still use it today, slightly modified.
If you check the sequence of major scale notes in our modern tuning system, you'll find that the sequence of root -> fifth -> second -> sixth -> third -> seventh -> fourth is indeed a sequence of fifths (7 semitones each jump), except for the fourth, which is only a 6 semitone jump so that the gap from fourth to the octave would be a perfect fifth and thus complete the cycle. This was squeezing the ancient system onto a modern instrument with twelve equally spaced pitches, but it works well enough.
Thus the major scale is at least 2,600 years old (and is probably much older).
There's also a surviving gravestone on which was written a short piece of ancient music. It's called the Song of Seikilos. That's it to the left.
The first section is a standard inscription. It says something like: I am a gravestone. Seikilos placed me here, an everlasting monument of deathless remembrance.
Then the next section is a song! This is hugely important because it's the oldest known complete song for which there is no doubt whatsoever what the notes are. The lyrics are the engraved words (of course). But just above the letters you'll see funny, smaller symbols. That's the music notation. The position of the symbol above the word shows when to play the note as you sing. Since it has the lyrics and the melody, this is a lead sheet, in modern parlance.
This gravestone dates to zero AD, give or take a hundred years. There are fragments of music that are very much older, but none complete, and everything older than the Song of Seikilos requires some educated guess work to reconstruct it.
The lyrics say this:
While you live, shine,There have been lots of renditions of the song. Here's an instrumental only version that I suspect is very close to what you would have heard if you'd met Seikilos. This is played by researcher Michael Levy, who built a period instrument.
Have no grief at all.
Life exists only for a short while,
And time demands its toll.