Prehistoric muisc is the first era of music.(that we know of). I couldn't find a lot of info on this era and it's basically any music that "existed before the advent of any currently extant historical sources concerning that music." (that's from the wikipedia.)
Now I'm pretty sure the first things that were our "instruments" were our own bodies and voices. Now some people believe that music may have originated from natural noises and ryhtems.
The prehistoric era of music may have ended when we learned how to write. With it came the invention of "songs". They used double pipes like the old ancient greeks. Basically they made "songs" with instruments and made more organized ryhtms and music.