Earth 2: Special Low Frequency Version poses a question that has never been satisfactorily answered. Released in 1993, it remains a void at the heart of the grunge era. Stripped of drums, vocals, lyrics and conventional song structures, the album eschews the language of rock music.

Earth 2 runs for 73 minutes and comprises three tracks – ‘Seven Angels’, ‘Teeth Of Lions Rule The Divine’, ‘Like Gold And Faceted’ – whose titles adopt a religious register, but never commit fully to it. Dylan Carlson and Dave Harwell create a slow-motion pyroclastic flow of guitars. Tightly woven chromatic melodies flame out at intervals, licking at the gigantic underside of the “songs”.

The album leaves the listener grasping for a way to anchor themselves within it. Recorded in August 1992 in Avast studios in Seattle with co-producer Stuart Hallerman, the session atmosphere was relaxed, though Carlson has said he regrets not recording at their full-blown live volume. The album had a counterpart in Melvins’ droned-out Lysol, released that November. One of the connecting points between the two bands was Melvins bassist Joe Preston, who had contributed to Earth's first EP, Extra-Capsular Extraction, in 1991. And of course Kurt Cobain, friend of both bands, who contributed some vocals to Extra-Capsular Extraction. The final track on that EP, the fourteen-minute cyclical drone of ‘Ouroboros Is Broken’, signposted the album to follow.

Whereas Earth were trying to outdo Melvins, Earth 2 is often referenced in relation to the band that took it for their own blueprint: Sunn O))). Joking that the Earth revolves around the Sun, the latter’s debt to Earth 2 can never fully be repaid. Years ago, Julian Cope described the music of Sunn O))) to me as an “interface with the total barbarian self”. In Cope’s field of “archaeo-sonics”, this makes sense. There is a continuum, in Cope’s mind, between the effect of air moving through a neolithic burial chamber, producing a drone that a shaman could use to terrify their initiates, and the frequencies you can feel at Sunn O))) gigs.

Drone and ambient metal is often invoked in elemental terms. There is something antediluvian and beyond about it. Pierce the earth’s crust, and there is liquid fire, ever so slowly shifting the tectonic plates we inhabit. Such music is envisaged as massive and totally beyond our control. It infuses the foundations of civilization. As Attila Csihar intones on Sunn O))) track ‘Aghartha’, named for a legendary subterranean kingdom: “Into the memories of the consciousness of ancient rocks/ Nature’s answer to eternal question”.

Stripped of the trappings of modern pop and rock, ambient metal invites a search for answers to the bigger questions. Ancient musical modes are resurfaced to get us closer to a putative godhead.

“One of the reasons that heavy metal occasionally sounds like religious music is because most religious music was inherited from heathen times,” Cope told me. “And so when you reduce the music to its lowest common denominator, it goes down to those modes that were most useful to the ancient people.”

You can really feel this at the 13-minute mark of ‘Teeth Of Lions Rule The Divine’ on Earth 2. Whereas a lot of the album feels like being dangled over a precipice, the riff (and I’d struggle to call many of the record’s guitar motifs “riffs”) resolves itself with a crushing, near ecstatic purpose. Perhaps this riff is an example of Earth being “useful” for the purposes of active meditation on life’s bigger questions.

Except there’s a problem. I don’t think the members of Earth were seeking to be useful, or provide any answers, with Earth 2. The whole album feels like an exercise in discomfiting and bamboozling the listener. In the press material for the album after it was released, they mocked the idea of the music’s meditational properties in a series of fake testimonial quotes: “... found it difficult to think of the things that disturb me… Afterwards, everything seemed right with the world.” “Forget drugs and alcohol… I am now very, very mellow!” “A new, yet seemingly ancient kind of experience… Very unusual!!”

In the band photo accompanying the original release, Dylan Carlson wore a Morbid Angel T-shirt. “I like metal”, was the message. And maybe, “This Earth 2 album is metal.” As a death metal band, Morbid Angel’s musical language was rigid and clear. Theirs was a Lovecraftian-cum-satanic world, whose prejudices were barely kept below the surface. For this reason it feels to me that Carlson was gently mocking us with the T-shirt. Earth paid zero attention to predetermined (sub)genre limitations.

“Wait until you listen to Earth 2!” he tacitly taunted. “What’s our belief system? What’s our perspective? What language are we speaking?”

I had a profoundly unsettling experience listening to Earth 2 on an evening walk in early October. I left in the daylight and returned in the darkness. I took the route I usually do, up from the village where I live towards a local geological formation known as the Devil’s Punchbowl. The legend has it that Thor was fighting with the devil and scooped up a massive fistful of dirt to lob at him. The resulting crater fills with mist on Autumnal mornings, giving it the appearance of being filled to the brim with foggy punch.

I walked up the hillside, through yew trees and along sandy paths, towards Gibbet Hill. This is the site where three robbers who murdered a sailor on the Portsmouth road in 1786 were left to rot for all to see, and is reputedly haunted. The isolation of the walk doesn’t usually bother me, but after sunset, as the night drew in, the sheer relentlessness of Earth 2 started to have an uncanny effect.

‘Like Gold And Faceted’, the album’s last track, is half an hour long. Its interspersed splashes of reversed cymbals and other percussion (performed by Joe Burns) fail to alleviate the pressure it exerts. I started to feel an immense sense of dread. Instead of the music flooding my senses, it felt like it was peeling back reality itself. The neverending sustain and feedback of the track didn’t fill the countryside around me with warming distortion, but seemed to suck the material world away. What should have been billowing, and comfortably weird, became empty and eerie.

Listening to Earth 2 that evening, it was as if my consciousness was dissolving. I felt panicked and hurried home to “reality” as fast as I could. If we accept psychoanalyst Jacques Lacan’s view that the unconscious is “structured as a language”, it feels to me that the album is asking a question that uncovers a site “where a traumatic truth speaks out”. That latter quote is Slavoj Žižek’s interpretation of how Lacan saw the unconscious talking and thinking. “What awaits me ‘there’ is not a deep Truth that I have to identify with, but an unbearable truth that I have to learn to live with,” he continues.

I began to wonder whether I had uncovered an “unbearable truth” at the centre of Earth 2, or whether it had affected my cognition to the point where it had revealed something under the surface of everyday reality. This is the Real – the ineffable that surpasses rational understanding, and language itself.

Prompted by a thread about intense films you should watch once, and probably only once, I’d recently seen the 1956 documentary Night And Fog, directed by Alain Resnais. A chiling, dispassionate examination of the Nazi concentration camps, it derives its power from a deliberate lack of over-explanation. Its imagery – the emaciated patients in a hospital, an autopsy table, a fastidious Nazi logbook, piles of personal belongings, piles of bodies – is served up to the viewer with minimal context. Unspeakable and obscene truths are left hanging.

In an interview about the film for the Criterion Collection, The Act Of Killing director Joshua Oppenheimer says: “The things that the film doesn’t ask create questions that haunt the film almost as powerfully as those that are asked explicitly.”

I feel that Earth 2 functions similarly – it is asking, and withholding, uncomfortable questions. But about what, exactly?

In the face of these questions, other artists have attempted to provide answers. In 2002, Sunn O)))’s Stephen O’Malley and Greg Anderson formed a doom “supergroup” (not that there’s anything “super” about doom) with Cathedral vocalist/Rise Above label owner Lee Dorrian and Iron Monkey drummer Justin Greaves, called Teeth Of Lions Rule The Divine.

In appropriating the song title from Earth 2, O’Malley stressed that the phrases from the Book of Revelation it makes composite were “not a Christian referential point as such but rather the poetic, surreal and apocalyptic visionary one.” As for the conditions recording their only album, Rampton, Greaves once told me, “The Sunn O))) amps were like foghorns going off in my face, I had to wallop the drums just to be heard.”

The album was named after the Rampton psychiatric hospital in Nottinghamshire. It called back to an album by Come, formed by the teenage William Bennett prior to his power electronics group Whitehouse. Most recently in pop culture, the BBC television drama The Reckoning portrayed Steve Coogan as Jimmy Savile taking Rampton patients to the beach at Scarborough for a day out.

On the opening 29-minute 'He Who Accepts All That Is Offered (Feel Bad Hit Of The Winter)', feedback is laid down which Greaves ploughs against with six minutes of lead drums. His playing is improvised and unrehearsed. He leads the main riff out in a processionary manner, then punctures it with flurries of fills. Eventually the vocals spew forth in an atonal, incantatory sermon: “Within her hands are gifts for the damned/ You take them all/ Consume the pills, the acid, the booze/ Weakness can't refuse/ White speed, brown smack, bone pipe filled with crack/ There's no turning back/ Mushrooms and cocaine fight wars within your brain/ You can't stop the pain/ Your mind is ablaze, bleak streets are in flames/ You burn in the maze”.

It's a lyrical and musical repudiation of Queens of The Stone Age's ‘Feel Good Hit of the Summer’, with its stoned mantra of “Nicotine Valium Vicodin Marijuana Ecstasy and Alcohol . . . c-c-c-c-c-COCAINE!”, a celebration of drugs that had helped make QOTSA’s Rated R album a hit the previous year. ‘He Who Accepts’ relocated sunny, Palm Springs desert rock hedonism and drained it of colour, throwing it into the dreary streets and feeding it the bad drugs of a small town in the British Midlands. The song slow-heaves itself on, like a massive jet trying to take off underwater.

Teeth Of Lions Rule The Divine took Earth 2 and tried to pin it down. By adding drums, vocals, lyrics, and moving the realm of the unconscious to a real-world analogue for the psychiatrically disturbed, they translated it into their own language. But theirs is doom metal, and the geist of Earth 2 soon vanishes with the mounting groove and Rampton’s more obvious, metallic musical configurations.

The same goes for the remixes/reconstructions of Earth 2 that have been commissioned for its re-release, dubbed Earth 2.23 Special Lower Frequency Mix. ‘Angels’, The Bug feat. Flowdan remix of ‘Seven Angels’, pumps urgency into the original with its ‘foot to the pedal’ refrain. The duo supplant the original’s meandering exploration with the focused overstimulation of a world scrupulously documented for “likes” and “views”. The Bug’s other (solo) remix of ‘Like Gold And Faceted’ transmutes it to a lower realm of even greater sub-frequencies where you can hear the air being pushed through the track – ghosts rushing to oblivion.

‘May Your Vanquished Be Saved From The Bondage Of Their Sins’ by Loop’s Robert Hampson is a Ligeti-esque cosmic nightmare. Untethered from our earthly realm, the lashings of the bass guitar seem to simulate a destructive event. Adrift in LSDeified space, cold comfort comes by way of fizzing guitars panning in and out of the mix like barely intercepted transmissions. Brett Netson’s take on ‘Teeth Of Lions Rule The Divine’ begins with an engine growling to life. In his hands, the song is the ghost of a new machine – burnished and eternal.

Faced with the formlessness of the Real represented by Earth 2, Justin Broadrick erects a scaffold of his own. The grinding beats of his own remix of ‘Teeth Of Lions’ situates it in the slavestate where weak flesh meets the architecture of authority, and with it the howls of human suffering. Earth’s unspeakable truth is entombed within Broadrick’s “brute concrete reality” (to borrow a phrase Simon Reynolds used in his Melody Maker review of the Godflesh EP).

As excellent and fascinating as these reinterpretations of Earth 2 are, they speak the album in their own languages. It feels like they take us away from the “truth” of the record, whatever that is.

Dylan Carlson moved Earth away from Earth 2 as well. By 2005, with Hex; Or Printing In The Infernal Method, Carlson delivered the band into a soundscape encoded in another’s language: that of Cormac McCarthy and his 1985 novel Blood Meridian. Earth made its home in the occult, blood-soaked desert of the Old West and McCarthy’s character the judge: “The desert upon which so many have been broken is vast and calls for largeness of heart but it is also empty. It is hard, it is barren. Its very nature is stone.”

Thirty years on, Earth 2 still feels like an aberration in the Seattle sound of 1993 – an overwhelming occurrence without easily identifiable origin, and a law unto itself. But listen to ‘4th Of July’ from Soundgarden’s mega-smash Superunknown album released the following year, and you can hear Earth slackening the string tension in Kim Thayil and Chris Cornell’s titanic, bowel-scraping guitars. Black Hole Sunn O))), if you can forgive me.

The title of Earth’s debut album disguised itself as a follow-up – to some imaginary, “normal frequency” predecessor. (OK, it was technically their second release.) Its music shows us something which can be interpreted as primordial – familiar yet foreign, unnerving, primitive, deadly. What it unveils is a place beyond the usual confines of orderly, structurally sound expression.

We still don’t speak the language of Earth 2. It reaches to that truth where perhaps authentic (Real) heaviness lies. The most disconcerting thing about the question it demands us to answer, is that it is impossible to know exactly what it is asking.

Earth 2 and Earth 2.23 are out now on Sub Pop