Simplify the following text for a Grade 4 native English-speaking person.
Original: The unexpected success of `` Smells Like Teen Spirit '' in late 1991 propelled Nevermind to the top of the charts at the start of 1992 , an event often marked as the point where alternative rock entered the mainstream . `` Smells Like Teen Spirit '' was Nirvana 's first and biggest hit , reaching number six on the Billboard Hot 100 and placing high on music industry charts all around the world in 1991 and 1992 .
Simplified: Smells Like Teen Spirit was released in 1991 .