Evan rejoined the band in early 1970. He had stayed in London since the John Evan Band broke up, living with Anderson, and began studying music at the University of London. The pair did not see much of each other because of Jethro Tull's increasing workload, and Evan was reluctant to rejoin because of his studies, which gave him access to a free studio. He played as a session musician on the next album, Benefit(1970), following which Anderson said they needed somebody to play the keyboard parts on tour. His tutor eventually persuaded him that it was a good idea, and Evan formally joined. The album reached No. 4 in the UK and No. 11 in the US, and allowed the group to sell out 20,000-seat arenas, establishing themselves as a premier live act.In August, the band played to one of their largest audiences at the 1970 Isle of Wight festival.
The Isle of Wight appearance was followed by another US tour, following which Cornick left the band. He was keen to socialise on tour, while the other members became more reclusive and introverted. Cornick said he was fired by Anderson, while the band's official website said he was "invited to leave" by Ellis, but given full support and encouragement to form his own band. Cornick subsequently formed Wild Turkey, a band which he revived for Jethro Tull fan conventions decades later. He died in August 2014.
Anderson invited Jeffrey Hammond to replace Cornick, buying a new bass for this purpose. However, Hammond had not played an instrument since going to art school shortly after his time in the John Evan Band, and was chosen more for his social compatibility with the other band members than for his musical skills.