A tune played on a reproduction of a flute dated to about 35,000 years ago: http://tripping-the-world.com/01-hear-the-oldest-instrument-in-the-world.html. Although not credited, this is presumably the reproduction by Wulf Hein of the Hohle Fels notched flute, made from the wingbone of a vulture, https://www.youtube.com/watch?v=4YqcZ4XCeuU, ... not really the oldest known instrument, just the oldest object we're sure is an instrument and have been able to recreate.

Pentatonic scale. Good lord, they played the blues during the Neolithic! Bet the ice age had something to do with it.