A brief summary of how the Gates of Hell were opened:
Tumblr user ChaosControlled123 has transcribed a piece of music written on the butt of a guy being tortured in hell from an medieval painting.
It appears that the university student named Amelia is the first person to ever actually attempt to play the song.
Most likely, this has summoned Satan and he will unleash his band of hellbeasts and succubi to torture us in the last of our mortal days.
This is The Garden of Earthly Delights by early Netherlandish painter Hieronymous Bosch:
The right panel depicts Hell, including a guy with a music sheet tattood on his buns:
Amelia explains: "I decided to transcribe it into modern notation, assuming the second line of the staff is C, as is common for chants of this era."
Behold: the haunting refrain of the 600 year old butt song from Hell:
Thanks to Rusty Foster's Today In Tabs newsletter for the tip.