Forty-two years ago today, on Friday the 13th, the gates of hell opened up and belched forth Black Sabbath. Upon its release, the Birmingham band's eponymous debut album instantly became the heaviest, scariest, most evil record of all time, and it still ranks right up there.

Calling this record "influential" doesn't quite do it justice. Without hyperbole, Black Sabbath changed rock music. While it's hard to credit a single album for the birth of heavy metal, it's altogether fair to classify all hard rock as pre- and post-Sabbath.

To be sure, Sabbath was hardly the only band pumping out heavy blues in 1970. But nothing that came before was this heavy, and certainly nothing was this dark. Don't believe us? Then what say we take a look back on the heaviest albums to be released prior to Black Sabbath?

To save you a trip to Wikipedia, Rocks Off has helpfully assembled the following chronological list of the 10 heaviest records put out before 1970. Most of these albums are great, even legendary. But in terms of heaviness -- real, headbanging heaviness-- there's really no comparison.

Jimi Hendrix Experience, Are You Experienced? Released May 1967

History's unanimous No. 1 Guitar God may have been the single biggest six-string influence on what would become heavy metal. Hendrix revolutionized the way the electric guitar was approached in the late '60s, with incredible waves of distortion and feedback beyond anything that had been heard at the time. Noel Redding's thick, sinuous bass and Mitch Mitchell's pounding drums on tracks like "Fire" and "Purple Haze" would heavily inform Sabbath's mighty rhythm section a couple of years later.

The band's subsequent album, Electric Ladyland might have also made this list, but you get the point.

Cream, Disraeli Gears Released November 1967

If Black Sabbath can be credited as the beginning of metal (they can), then Cream is perhaps the beginning of the beginning. The prototypical power trio basically invented the brand of stomping, semi-psychedelic blues-rock that would later be explored by Hendrix, Led Zeppelin, Sabbath and about a million others in the late '60s and '70s.

Few made it sound anywhere near as compelling or heavy than Cream. Ginger Baker's crashing drums on this record are an obvious influence on Bill Ward's playing on Sabbath's debut a couple of years later. Guitarist Eric Clapton would eventually prove somewhat influential on metal, as well.

Steppenwolf, Steppenwolf Released January 1968

Steppenwolf ascended to hard-rock immortality following the iconic use of its pre-metal classic "Born to be Wild" in the biker-movie smash Easy Rider. The song's legend is well-earned -- it gives Steppenwolf as legit a claim as anyone to coining the phrase "heavy metal," and "Born to Be Wild" still rocks as hard today as ever it did.

But there are other heavy gems to be savored on this album, most notably the crushing "Hootchie Kootchie Man" and "The Pusher."

Blue Cheer, Vincebus Eruptum Released January 1968

This late-'60s glorification of heavy blues, strong drugs and unhealthy volume serves as one of the primitive pillars of heavy metal. Blue Cheer perfected the sludgy, doom-laden sound of Marshall-wielding acid casualties years before Black Sabbath hit the scene. It may not be possible to play the blues any louder or heavier than the example set on Vincebus Eruptum, but that hasn't stopped four decades' worth of garage bands from toking up and trying.

Iron Butterfly, In-a-Gadda-da-Vida Released June 1968

More than any other other album, In-a-Gadd-da-Vida marks the turning point when acid rock began to take a darker, heavier turn toward what would soon be called heavy metal. Remembered principally (and rightly so) for the 17-minute title track that consumes the record's entire second side, this proto-metal masterpiece was an instant smash, eventually selling more than 25 million copies.

The track's moody guitar and bass ostinato that serves as the foundation for several endless solos is precisely the kind of simple, weighty riff that Tony Iommi would soon be perfecting across the pond.

Deep Purple, Shades of Deep Purple Released July 1968

Though Deep Purple wouldn't truly cement their status as heavy metal godfathers until the group's second iteration released In Rock in 1970, the band was already exploring some terrifically heavy sounds on its '68 debut. Purple created a truly gigantic sound through the ultra-tight interplay of guitarish Ritchie Blackmore and organist Jon Lord over the rollicking rhythm section of bassist Nick Semper and drummer Ian Paice. The group's cover of "Hush" is the best-remembered track from this album by far, but songs like "Mandrake Root" hinted at the heaviness to come.

Led Zeppelin, Led Zeppelin Released January 1969

Perhaps Black Sabbath's greatest rival for the title of original heavy metal album, Led Zeppelin was the most extreme iteration yet upon its release of the heavy British blues-rock pioneered by Cream. Its histrionic vocals, crunchy guitar and punishing drums set the template for thousands of metal records to come.

More than 40 years later, rock and roll still doesn't get much heavier than "Dazed and Confused," a nifty American folk tune that Jimmy Page twisted into a gargantuan, brooding thunderclap that's still blowing teenagers' minds to this day.

MC5, Kick Out the Jams Released February 1969

The MC5's counterculture classic Kick Out the Jams may have gone on to become a bigger influence on punk than heavy metal, but there's no getting around the fact that the Detroit rabble-rousers were pumping out some of the heaviest music the world had ever seen back when it was released in 1969.

The album's immortal title track alone is filled with more righteous, howling fury than pretty much anything that came before and much of what's come since. It doesn't hurt the record's heaviness quotient that it was recorded in two days over Devil's Night and Halloween 1968, either.

The Stooges, The Stooges Released August 1969

Ron Asheton's distorted power-chord riffs captured on this proto-punk monument were certainly among the rawest recorded in the era, but The Stooges' real heaviness stems from the unremitting nihilism on display in the band's lyrics and attitude. The majority of this album was culled from the Stooges' incendiary live show from '69, blood- and peanut butter-smeared performances that set a weird and dangerous new precedent for rock extremity.

High Tide, Sea Shanties Released October 1969

Despite being one of the late '60s' heaviest bands, High Tide never achieved the contemporary acclaim or legendary status as the other groups on that list. Hell, we couldn't even find any of their songs on YouTube. Part of the reason is that they simply weren't as good -- long jams featuring violin(!) solos and vocalist Tony Hill's Jim-Morrison-on-barbituates delivery aren't quite as compelling as they might sound. Still, the group's incredible guitar crunch and doomy lyrics on its '69 debut were ahead of their time enough for inclusion here.