The 1970s were probably the most evolutionary decade for rock and metal. The '60s saw bands such as The Beatles and the Rolling Stones completely dominate the charts until the trifecta of metal pioneers were born a few years later — Black Sabbath, Led Zeppelin and Deep Purple.

The three aforementioned bands are often credited for revolutionizing rock 'n' roll and, shall we say, inventing heavy metal as we know it today. But there were plenty more that often go unseen today.

It's easy to listen to their discographies and write them off as classic rock, especially comparing their sound to what metal is today. But no other bands were bringing in such thunderous volume, distortion and intricate guitar playing at the time. Once 1970 came along, there were a plethora of other bands following suit, combining elements of blues with acid rock and psychedelia.

That was half a century ago, so to commemorate rock's heavier transition and metal's origins, we wanted to revisit 20 albums turning 50 this year.

While some of the artists might seem like outliers compared to the styles we tend to focus on the majority of the time, without the foundation these artists set, bands like Metallica, Slipknot, Pantera and Tool wouldn't exist today. And for those of you who are interested in learning more about the history of how metal's roots were formed, these albums are a great start.

Top 70 Hard Rock + Metal Albums of the 1970s