Just like The Beatles changed pop music 30 years prior, Nirvana's breakthrough album achieved the same level of power in terms of changing pop music. Before Nirvana came along Pop music was in a tired slump, quality music at times but "nothing new" is the way I look at it. Then, like a blip in a radar screen, for a very short time we were all exposed to a new kind of approach-"Grunge". Happy lyrics all of a sudden didn't need to be , power chords and in-coherent musings were cool. During its peak, brought on because of bands like Nirvana, every other month a new band from Seattle was making its way around the charts, some from that time are still with us, Pearl Jam and others. Do you think EMO would have ever become what it is/was if were not for Nirvana?