It was 40 years ago, 1972. It is a breakthrough year in the history of Classic Rock ( including subgenres Progressive and Heavy Metal).

Despite the fact that many of the true heavyweights of the industry did not release an LP.

The Beatles had broken up,Hendrix was dead, Morrison was dead. Eric Clapton was off the radar dealing with personal problems. Dylan, The Who, Led Zeppelin did not release studio albums. Pink Floyd had yet to climb into the higher ranks of Rock supremacy, releasing the marvelous, however obscure and aptly named 'Obscured By Clouds' LP....not to be one of their most reknowned works, however.

Also consider, Woodstock heavies Jefferson Airplane and the Grateful Dead were becoming 60's icons, but found tough going getting airplay in the early 70's...obviously they were ( as they still seem to be ) linked to the turbulant era of the late 60's. Crosby , Stills, Nash & Young...that ship already sailed and now the artists were all persuing solo projects, with Young the only one of the four to breakthrough to the manistream in 72, Stills enjoyed some minor success. Santana was heading off into a more Jazz influenced territory with 'Caravanserai'...not one of their most popular LPs.

But, all that taken into consideration, these groups released major Rock LPs , that are considered classics by many:

Edgar Winter Group-They Only Come Out At Night.
Neil Young-Harvest
Yes-Close To The Edge
Moody Blues- Seventh Soujourn
Deep Purple- Machine Head
Mott The Hoople- All The Young Dudes
Rolling Stones- Exile On Main St. (the exception to the rule as the Stones were huge stars at this point).
Uriah Heep-Demons And Wizards
ELP- Trilogy
Jeff Beck Group-s/t
Black Sabbath- Black Sabbath VOL. 4
Alice Cooper- School's Out
Elton John-H*nky Chateau...sorry, BDC WON'T ALLOW THE WORD!
Humble Pie- Smokin'
David Bowie- the rise and fall of Ziggy Stardust and the Spiders From Mars
Jethro Tull- Living In The Past
ZZTop- Rio Grande Mud
the Allman Brothers- Eat A Peach
the Doobie Brothers- Toulouse Street
J. Geils Band - Full House ( live LP- BUT POSSIBLY THEIR BEST!)
Cactus- 'Ot 'N' Sweaty



...in addition , these groups released their marvelous debut LPs:

Steely Dan- Can't Buy A Thrill
The Eagles- s/t
Foghat- s/t
Blue Oyster Cult - s/t ( it was not uncommon for groups to debut with self- titled LPs, as you can see.

Considering all the inactivity from the mega-stars and super heavyweights of the era...WOW!!!