In August, music magazine NME revealed that the band were discussing ideas for their second album, quoting Stockdale as saying "I feel like we've got a lot more to say".

"[17] After more touring and a brief period of inactivity with few updates regarding new material, American magazine Rolling Stone reported in November 2007 that "Wolfmother [were] hard at work on a new album".

The first new original material, since the release of "Pleased to Meet You" in 2007, appeared during the band's first performance in nine months at the Queensland Gallery of Modern Art (QGMA) on 12 April 2008 in the form of four new songs:[20] "Back Round", "The Violence of the Sun", "Monolith" and "Inside the Mountain".

[24]Within days of the rumours surfacing, reports were updated to make the breakup official; bassist and keyboardist Chris Ross and drummer Myles Heskett departed Wolfmother immediately due to "longstanding frictions".

[29][30] Following the performances the new members of Wolfmother, who had officially joined the band on 5 January 2009,[31] were confirmed as guitarist Aidan Nemeth, bassist and keyboardist Ian Peres and drummer Dave "Acosta" Atkins, and a new song called "Pilgrim" was mentioned.

[35] Stockdale began recording early versions of the new Wolfmother songs in his home-based studio before the new band members were officially unveiled.

[3][43] On 1 May, Wolfmother performed at the Natural History Museum of Los Angeles County, debuting new songs "Cosmic Egg" and "California Queen".

"[49] Shortly after this update, a link was posted on the Twitter page to a montage video of the band recording and mixing some songs on the album, including "Back Round" and "Pilgrim".

[54] Cosmic Egg was mixed in Pasadena, California shortly after the recording of the album by Stockdale, producer Alan Moulder and Joe Barresi.

[36] On 18 June, Stockdale reported that he had "Just heard a mixed and mastered version of Cosmic Egg the song", describing it as "of[f] the Richter Scale".

[3] In a pre-release interview with the singer-songwriter, Rolling Stone Australia described the album as "vintage Wolfmother", mentioning features and qualities such as the "distorted, frenetic, bass-heavy sounds of 'White Feather'" and "the epic 'In the Morning'".

[36] MTV also hinted at the style of the album early, explaining that "Tunes like 'California Queen' and 'Sundial' chug along on meaty chords, dive into sludgy breakdowns and sizzle with Stockdale's flame-kissed solos".

[57] Writer James Montgomery went on to add that "'Far Away' and 'Pilgrim' are moody, fog-machine ruminations on astral planes and mythic realms, floating on pealing organ lines and stony synths".

[57] In August 2009, Spin published a track-by-track review of Cosmic Egg, revealing the following song descriptions: "California Queen" [...] From the first head-banging riff, to Andrew Stockdale's Ozzy-with-his-balls-in-a-vice vocals, to bongy, fantastic lyrics about "Standing in front of the rainbow" and "Homegrown hydroponics," Wolfmother still parties like it's backstage at a Uriah Heep show in 1972.

[76][77] In September Cosmic Egg was delayed further "to allow [the band and management] more time to complete the artwork and manufacture the various release configurations".

Tiffany Bakker of Rolling Stone Australia magazine described the songs on the album as "vintage Wolfmother – heavy Sabbath-esque riffs and heaving basslines mixed with the distinctive wail of Andrew Stockdale that all add up to something raucous and thrilling".

[36] In another pre-release interview with Stockdale, music website Artistdirect summarised the album as "a powerful and poignant rock n' roll record with all the ingredients of a modern classic".

[74] Writer Rick Florino went on to describe specific strengths of the album, including "unforgettable riffs on 'Pilgrim' and 'Sun Dial'" and "the infectious hook on 'New Moon Rising'".

[74] Florino also identified "Pilgrim" as "lyrically [...] stand[ing] out", described "Sundial" as "like one of those crazy Black Sabbath stories" and outlined the bass performance as "pretty killer".

[74] MTV writer James Montgomery explained that "Cosmic Egg shouts very loudly, showcasing the added punch of three new musicians [...] and taking everything that made Wolfmother's self-titled debut such a smash – namely, gut-busting riffs, incendiary solos and bong-glazed mysticism – and cranking it to the absolute maximum".