New study charts the evolution of music

The evolution of western pop music, spanning from 1960 to 2010, has been analysed by a team from Queen Mary College (University of London) and Imperial College London who looked at more than 17,000 tracks from the US Billboard Hot 100 and found three music revolutions - in 1964, 1983 and 1991: in 1964 the invasion of British bands - from the Beatles to the Rolling Stones - introduced a radical new rocky sound; New technology, synthesisers, samplers and drum machines, drove a second major style shift in 1983; The third revolution, - the biggest change - came in 1991, came about when rap and hip-hop went mainstream.

Researchers found that music constantly evolved and change throughout the 50-year period.  In the early 1960s, chords called dominant sevenths, found in jazz and blues, started to die out. Minor seventh chords were introduced through funk, soul and disco in the 1970s and whilst this wasn't a 'revolution', they haven't gone away and new songs still heavily use these chords, but the homogenisation of pop began in the 70s.  Drum machines, synthesisers and the rise of arena and stadium rock in the 80s led to a lack of music diversity - 1986 was the most repetitive year on record. 

http://www.bbc.co.uk/news/science-environment-32599916