On this day in 1967, The Beatles continued work on arguably their best song, "A Day in the Life." After a debate over how to end the track following the huge orchestral build-up (sustained choral vocals were considered, but scrapped), the group decided to simultaneously strike a massive E chord on three pianos and sustain the notes for as long as possible. Adding overdubs (and a contribution from producer George Martin on harmonium), the final resonating notes hang in the air for over 40 seconds on the recording. As the held chords faded on the pianos in the studio, the engineer had to crank the recording level, which picked up some incidental sounds (like a creaking chair and, certainly, something about Paul being dead) from the studio. That E-major chord that closes the song — and the whole Sgt. Pepper's Lonely Hearts Club Band album, considered one of the best ever — is widely considered one of the most famous chords in Rock/Pop history. Which means that The Beatles are responsible for the most popular opening chord in modern music — the mysterious G7sus4-ish that kicks off "A Hard Day's Night" — and the most notable final chord with the "A Day in the Life" finale. Below is audio of BTO guitarist Randy Bachman explaining the "Hard Day's" chord mystery (frustrated guitarists should feel better about their inability to figure it out), followed by today's biggest Pop superstar performing that famed final note from Sgt. Peppers.Click the jump for "Born This Day" featuring live footage from one of the final Sublime concerts with Bradley Nowell.