Have you talked to your children about The History of Heavy Metal? Perhaps it's time.
Artist Mike Hill, a longtime fan of heavy metal music, decided to make a "single drawing -- a giant timeline that contained every heavy metal band from the 1970's to present day, organized by subgenre."
It has since evolved into four parts, and even if you don't know Angel Witch from Morbid Angel, the art pieces themselves are worth a look simply so the viewer can marvel at what a monumental task Hill assigned himself.
The "Metal Subgenre Popularity Index" has an almost geometric-abstraction look, until a closer examination reveals that it's a functioning chart.
Hill keeps a blog about his endeavor too.