Nirvana stole the riff from Killing Joke
Killing Joke stole the riff from the Damned;
the Damned stole the riff from the Moody Blues;
Moody Blues stole the riff from Chuck Berry;
Chuck Berry stole the riff from Glen Miller;
Glen Miller stole the riff from Gershwin;
Gershwin stole the riff from an Irish folk song;
The Irish stole the riff from a Medieval knight chant;
Medieval knights stole the riff from a Hebrew prayer;
The Hebrews stole the riff from Pagan priests;
Pagans stole the riff from sub-Saharan aborigines;
Aborigines stole the riff from Australopithecus Africanus; Australopithecus Africanus, after eating too many beans one night, created the riff....but it was long after the big bang.