On the other hand, music existed for THOUSANDS of years without notation. We have no idea how the psalms were sung or what Roman or Greek music sounded like because there was no way at all to write it. The earliest efforts to record music in the ninth-century were just squiggles that told monks in choir which words to go up or down in pitch on.
There has been notated music found on ancient Greek Urns. It has been recorded. Classical Indian music has been notated for a long time. I'm willing to bet notation has been around far longer than that, in some form in many literate societies. You are correct in the development of modern notation.
Reading music notation is not so difficult or mysterious that it is even a high road to take. It's not the easiest thing in the world, but I've taught everyone from Kindergarden kids (it's rare to get a kid that young, but it's a private school so I'm dealing with the occaissional really bright kid) to old farts to do it, at least at a functioning level. Not professional level but enough to read or write easier standards.
Music notation was taught as a part of regular school curriculum in the dark ages of the 60's I was taught one octave on a cheap xylophone, with the rest of the 2nd grade class, recorder in 3rd or 4th grade and sight singing in 5th and 6th. This wasn't world class learning here, but at one time musical notation was taught to everyone.