Music Timeline by Google Research
An interesting visualization. Wondering if there would be a difference if you would take iTunes instead of Google Play Music. 
Music TimelineThe Music Timeline shows genres of music waxing and waning, based on how many Google Play Music users have an artist or album in their music library, and other data (such as album release dates). Each stripe on the graph represents a genre; the thickness of the stripe tells you roughly the popularity of music released in a given year in that genre.
