We live in an age of untimely surfacings. Across the Arctic, ancient methane deposits are leaking through “windows” in the Earth opened by thawing permafrost. In the forests of eastern Siberia a vast crater yawns in softening ground, swallowing thousands of trees; local Yakutian people refer to it as the “doorway to the underworld”. In the “cursed fields” of northern Russia, permafrost melt is exposing 19th-century animal burial grounds containing naturally occurring anthrax spores; a 2016 outbreak infected 23 people and killed a child. Retreating glaciers are yielding the bodies of those engulfed by their ice many years before – the dead of the ongoing conflict in Kashmir, or the “White war” of 1915–18 in the Italian mountains. Near the peak of San Matteo, three Habsburg soldiers melted out of a serac at an altitude of 12,000ft, hanging upside down. At Camp One on Everest in 2017, after a period of unseasonal warmth, a mountaineer’s hand appeared, reaching out of the ice into which he had been frozen. Gold miners in the Yukon recently unearthed a 50,000-year-old wolf pup from the permafrost, eerily preserved right down to the curl of its upper lip.

Spring bulbs push themselves up into flower far earlier than a century ago. Last August’s heatwave in Britain caused the imprints of long-vanished structures – iron age burial barrows, Neolithic ritual monuments – to shimmer into view as parch marks visible from the air: aridity as x-ray, a drone’s-eye-view back in time. The same month, water levels in the River Elbe dropped so far that “hunger stones” were revealed – carved boulders used since the 1400s to commemorate droughts and warn of their consequences. One of the stones bears the inscription “Wenn du mich siehst, dann weine” (If you see me, weep). In northern Greenland, an American cold war missile base – sealed under the ice 50 years ago with the presumption that snow accumulation would entomb it for ever, and containing huge volumes of toxic chemicals – has begun to move towards the light. This January, polar scientists discovered a gigantic melt cavity – two-thirds the area of Manhattan and up to 300 metres high – growing under the Thwaites glacier in west Antarctica. Thwaites is immense. Its calving face is the juggernaut heading towards us. It holds enough ice to raise ocean levels by more than two feet, and its melt patterns are already responsible for around 4% of global sea-level rise.

These Anthropocene unburials, as I have come to think of them, are proliferating around the world. Forces, objects and substances thought safely confined to the underworld are declaring themselves above ground with powerful consequences. It is easy to aestheticise such events, curating them into a Wunderkammer of weirdness. But they are not curios – they are horror shows. Nor are they portents of what is to come – they are the uncanny signs of a crisis that is already here, accelerating around us and experienced most severely by the most vulnerable.

A hard hat from an oil worker lies in oil from the Deepwater Horizon oil spill on East Grand Terre Island, Louisiana, June 2010. Photograph: Lee Celano/Reuters

These unburials also disrupt simple notions of Earth history as orderly in sequence, with the deepest down being the furthest back. Epochs and periods are mixing and entangling. Our burning of the liquefied remains of carboniferous forests melts glacial ice that fell as snow in the Pleistocene, raising sea levels for a future Anthropocene. Both time and place are undergoing what Amitav Ghosh has called “the great derangement”, torqued into new forms by the scales and speeds of anthropogenic change at a planetary level. “The problem,” writes the archaeologist Þóra Pétursdóttir, “is not that things become buried far down in strata – but that they endure, outlive us, and come back at us with a force we didn’t realise they had, a dark force of ‘sleeping giants’,” roused from their deep-time slumber.

In the summer of 2010, I made the first notes towards a book called Underland, about burial and unburial, deep time and journeys into darkness, which would eventually take almost a decade to write. It was hard, that summer, not to think of the underland, for three extraordinary stories were unfolding, dominating global news for months: the Deepwater Horizon disaster, the entrapment of 33 Chilean miners beneath the Atacama desert, and the eruption of Iceland’s Eyjafjallajökull volcano.

On 14 April, following years of low-level activity, Eyjafjallajökull entered a violent phase of eruption. It ejected more than 250m cubic metres of tephra, creating an ash cloud that rose to five miles in height and caused the grounding of most flights within European air space. Rock dust was sucked into the lungs and engines of northern Europe, and settled on landscapes where it would form a thin strata layer in the future rock record. It took until the autumn for the volcano to be declared dormant, far longer for those who lived within its shadow to recover.

On 20 April, 41 miles off the Louisiana coast, the borehole of a semi-submersible oil rig called Deepwater Horizon burst. The rig-level blowout killed 11 crewmen and ignited a fireball that could be seen on shore. The rig sank two days later, leaving oil gushing from the seabed at a water depth of around 1,500 metres. More than 200m gallons of oil flowed into the Gulf of Mexico, rising as a slick on the ocean that was visible from space. It would take until the autumn to cap and seal the well successfully so that it could be declared “effectively dead”. The consequences for the ecosystems and coastal communities of the gulf persist today. Twice in a week, the underland erupted catastrophically into the upper world. A double hammer blow was dealt to our containment systems for Earth’s buried matter. One of these events was of human making, the other beyond human control. Both produced a global sense of unsettlement at such unruly, obscene surfacings.

The Grjótagjá lava cave, Iceland. Photograph: Umkehrer/Getty Images

Then on 5 August, while the oil and ash still drifted, a massive cave-in occurred in Chile’s San José copper and gold mine, trapping 33 miners at a depth of 700 metres: alive but seemingly beyond rescue. The world and I were gripped by the fate of the Chilean miners. Their situation triggered vicarious fears of claustrophobia and taphophobia. Their plight resembled the plot of both a contemporary thriller and a classical myth. It took 69 days to rescue the men, as their supplies of food and water dwindled. On 13 October they were all brought, one by one, to the surface via a drilled shaft, in a capsule designed with Nasa’s help. Around a billion people watched the men’s miraculous extraction, the mine’s most precious yield. Nasa’s involvement was appropriate – the men had returned from a realm as alien as that of deep space.

In December scientists revealed their discovery of a vast 'deep life' ecosystem in the Earth’s crust, twice the volume of the world’s oceans

We know so little of the worlds beneath our feet. Look up on a cloudless night and you might see the light from a star trillions of miles away, or pick out the craters left by asteroid strikes on the moon’s face. Look down and your sight stops at topsoil, tarmac, toe. I have rarely felt as far from the human realm as when only 10 metres below it, held in the shining jaws of a limestone bedding plane first formed on the floor of a warm Cretaceous sea.

The underland keeps its secrets well. Last December scientists revealed their discovery of a vast “deep life” ecosystem in the Earth’s crust, twice the volume of the world’s oceans, containing a biodiversity comparable to that of the Amazon, and teeming with 23bn tonnes of micro-organisms – hundreds of times the combined weight of all living humans. Only in recent decades have ecologists traced the fungal networks that lace woodland soil, joining individual trees into intercommunicating forests via a “wood wide web” – as fungi have been doing for hundreds of millions of years. The notion of discovering a new mountain in Britain is laughable, but in Derbyshire in 1999 cavers broke through into a cavern now named Titan, since confirmed as the biggest known natural chamber in Britain, large enough to hold St Paul’s Cathedral four times over. It was as if another Ben Nevis had been found, somewhere near Chesterfield. A thousand feet below ground in northern Italy, I rappelled into a huge rotunda of stone, cut by a buried river and filled with dunes of black sand. Traversing those dunes on foot was like trudging through a windless desert on a lightless planet.

The underland’s impenetrability to vision and its obstructiveness to entry have long made it a means, across world cultures, of alluding to what cannot easily be seen or said: trauma, memory, grief, death, suffering, the afterlife – and what Elaine Scarry calls the “deep subterranean fact” of pain. Deliberately to place something in the underland is often a strategy to shield it from view. Actively to retrieve something from the underland often requires effortful work, physical or psychoanalytical.

For nearly two decades I have been writing about the relationships of landscape and the human heart. I began on the summits of the world’s peaks, wishing to solve a personal mystery (why I was so drawn to mountains when young that I was, at times, ready to die for love of them) but also a historical one (why the western imagination underwent a revolution of perception concerning mountains in under 300 years, from superstitious fear to secular worship). From that high ground, over the course of five books and 2,000 pages, I’ve followed a downwards trajectory, exploring the storeys of matter that lie beneath the surface of both land and mind. “The descent beckons / As the ascent beckoned,” wrote William Carlos Williams in a late poem.

For years I travelled to places where the underland deepens drastically or has exerted particular force on the upper world: from bronze age burial complexes in south-west England, to remote Arctic cave-art sites on Norway’s northern coasts, and the blue depths of time archived by the ancient ice of Greenland. I accompanied those who have thought hardest about what is held beneath us and what rises to meet us, including archaeologists, glaciologists, nuclear scientists, urban explorers, mythographers, miners, historians of atrocity and physicists seeking “dark matter” in laboratories far underground. I filled dozens of notebooks, some of which were destroyed or rendered illegible by the environments in which I carried them. I spent time with remarkable people, including a mycologist called Merlin who conjured the wood wide web into visibility for me, and Bjørnar Nicolaisen, a Norwegian fisherman with seer-white eyes who led the resistance to plans for oil-drilling in pristine Arctic waters, at the cost of a crisis in his mental health.

Down into the ice, Greenland. Photograph: Helen Spenceley

I also gathered underland stories, from Aeneas’s descent into Hades, through the sunken necropolises of Italo Calvino’s Invisible Cities and the Wind Cave cosmogony of the Dakota Sioux, to accounts of the many cavers, cave-divers and free-divers who have died seeking what Cormac McCarthy calls “the awful darkness inside the world” – often unable to communicate to themselves, let alone others, what metaphysical gravity drew them down to death. Why go low? Obsession, incomprehension, compulsion and revelation were among the recurrent echoes of these stories – and they became part of my underland experiences, too.

Before beginning these journeys I was given a talisman; a small owl carved from a whalebone by an artist called Steve Dilworth. The minke whale from which the owl flew had washed up on a Hebridean shoreline; another untimely surfacing. Dilworth sliced one of its ribs into oval cross-sections, and then – with two blade-strokes for the eyes and two for the wings – he cut one of those cross-sections into the form of an owl. The object has an ice-age aura of making. He gave me the owl on the condition that I carried it with me, to help me see in the dark. I did so, though there were times I wished for blindness rather than owl-eyes. In the underland I have seen things I hope I will never forget, and things I wish I had never witnessed.

“We have never been modern,” writes Bruno Latour. Since before we were Homo sapiens, humans have been seeking out spaces of darkness in which to find and make meaning. The earliest known works of rock art in Europe – painted ladders and hand stencils on Spanish cave walls – have recently, astonishingly, been dated to around 65,000BP; more than 20,000 years before Homo sapiens is thought to have reached Europe. Neanderthal artists left these images, spitting mouthfuls of red ochre dust against their hands to make ghostly outlines on the cold rock.

I saw contemporary versions of those prehistoric hand prints in several of the places I reached. One autumn evening in the south of Paris I lowered myself into a shaft dug into the floor of a disused train tunnel, and entered the quarry and catacomb labyrinth that extends for more than 200 miles beneath Paris. We stayed down in that invisible city for three days – the longest I have ever gone without seeing sun or sky. One afternoon, traversing miles of flooded tunnel beneath Montmartre, we passed a stencilled hand print outlined in lime-green paint on a wall. It had been left by a Holocene graffiti tagger instead of a Neanderthal cave artist, using a spray can instead of a mouthful of ochre, but it shared the impulse to make a mark in the dark.

Reproduction of paintings of ‘Cueva de la Fuente de Salin’ in Altamira National Museum and Research Centre Photograph: Alamy Stock Photo

The oldest of underland stories – in fact, the oldest of stories – concerns a hazardous descent to reach someone or something consigned to the realm of the dead. A variant to the Epic of Gilgamesh, written around 2100BC in Sumer, tells of such a descent made by Gilgamesh’s servant Enkidu to the “netherworld”, to retrieve a lost object on behalf of his master. Enkidu sails through storms of hailstones that strike him like “hammers”, waves attack his boat like “butting turtles”, but he still reaches the netherworld. There, however, he is imprisoned, only to be freed when the young warrior Utu opens a hole to the surface and carries Enkidu back out on a lofting breeze. Up in the sunlight Enkidu and Gilgamesh embrace, kiss and talk for hours. “Did you see my little stillborn children who never knew existence?” asks Gilgamesh desperately. “I saw them,” answers Enkidu.

Yes, journeys into darkness have long been made to recover or to store what is precious (minerals, information, memories, the lost, the loved) and to dispose of what is harmful (waste, ghosts, poison, enemies, trauma). Classical literature is rich with what were known in Greek as the katabasis (the descent to the underworld) and the nekyia (the questioning of ghosts or gods about the earthly future). Contemporary versions of the nekyia are presently under way in Greenland and Antarctica, where polar scientists drill up ice core from hundreds of metres down and hundreds of thousands of years ago, scrying the stories this cryo archive holds in order to model future climate: scientist as haruspex, auger as augury.

I have never been in a more beautiful, frightening space than when abseiling into a glacial melt shaft on the east coast of Greenland; the glass-glint of its polished sides, its creaks and roars, its humming blue light – and the sense of dropping into a pore in the skin of an immense creature, possessed of a pliant, patient liveliness.

Whalebone owl by Steve Dilworth

It is a distinctive power of claustrophobia – more so than vertigo – that it retains its ability to disturb even when experienced indirectly as description. While being told stories of confinement below ground, people shift uneasily, step away and look to the light – as if words alone could wall them in. But still they listen. I remember as a 10-year-old reading the account, in Alan Garner’s novel The Weirdstone of Brisingamen, of two children descending the mining tunnels that riddle the sandstone of Cheshire’s Alderley Edge. Deep inside the Edge, the narrowing tunnels threaten to trap them: “They lay full length, walls, floor and roof fitting them like a second skin. Their heads were turned to one side … The only way to advance was to pull with the fingertips and to push with the toes, since it was impossible to flex their legs at all, and any bending of the elbows threatened to jam the arms helplessly under the body.” Then Colin’s “heels jammed against the roof: he could move neither up nor down and the rock lip dug into his shins until he cried out with the pain. But he could not move …”

Those passages took cold grip of my heart, emptied my lungs of air. Rereading them now, I feel the same sensations. But the situation also exerted an immense narrative traction on me. Colin could not move and I could not stop reading.

In his book Vertical, Stephen Graham documents the dominance of the “flat tradition” of geography and cartography, and the “largely horizontal worldview” that has resulted. We find it hard to escape the “resolutely flat perspectives” to which we have become habituated, Graham argues – and he finds this to be a political as well as a perceptual failure, for it blinds us to the sunken networks of extraction, exploitation and disposal that support the surface world. “The whole Earth is not solid but everywhere gaping & hollowed with empty rooms & spaces & hidden burrows,” wrote Athanasius Kircher in his epic early-modern exploration of the underland, Mundus Subterraneus (1665). Human activity has added hugely to these hollows since Kircher, drilling more than 50m kilometres of oil-field boreholes alone, showing ourselves to be a burrowing and burying species, as well as a building one.

“Force yourself to see more flatly,” orders Georges Perec in Species of Spaces. “Force yourself to see more deeply,” I would counter. Now, more than ever, we need to understand the underland. Our “flat perspectives” feel increasingly inadequate to the deep worlds we now fashion and inhabit – and to the deep-time legacies we are leaving.

“Deep time” is the phrase coined by John McPhee in 1981 to denote the dizzying expanses of Earth history that stretch in all directions from the present moment. It echoes John Playfair’s description of the “abyss of time” he glimpsed while viewing a strata unconformity at Siccar Point in 1788, when geology was first emerging as a science. McPhee and Playfair’s phrases both evoke a temporal vertigo. For deep time is measured in units that humble the human instant: millennia, epochs and aeons, instead of minutes, months and years. Deep time is kept by rock, ice, stalactites, seabed sediments and the drift of tectonic plates. Seen in deep time, things come alive that seemed inert. New responsibilities declare themselves. Ice breathes. Rock has tides. Mountains rise and fall. We live on a restless Earth.

There is a perilous comfort to be drawn from deep time. An ethical lotus-eating beckons. What does human behaviour matter when Homo sapiens will have disappeared from Earth in the blink of a geological eye? Viewed from the perspective of deserts or oceans, morality looks absurd, crushed to irrelevance. A flat ontology entices: all life is equally insignificant in the face of eventual ruin.

Maelstrom cave, Norway. Photograph: Helen Spenceley

We should resist such inertial thinking; indeed, we should urge its opposite – deep time as a radical perspective, provoking action not apathy. The shock of the Anthropocene requires a new time literacy, a rethinking of what the geologist Marcia Bjornerud calls “our place in time”. This is already happening. Deep time is the catalysing context of intergenerational justice; it is what frames the inspiring activism of Greta Thunberg and the school climate-strikers, and the Sunrise campaigners pushing for a Green New Deal in America. A deep-time perspective requires us to consider not only how we will imagine the future, but how the future will imagine us. It asks a version of Jonas Salk’s arresting question: “Are we being good ancestors?”

Rebecca Altman, an environmental sociologist, has memorably tracked the modern history of “time-bombing” – the toxic legacies that are left by one generation for its successors, of which high-level nuclear waste is the most obvious example. Time-bombing is already occurring laterally, of course. William Gibson famously remarked that “the future is already here, it’s just unevenly distributed”. In today’s Anthropocene, the affluent experience the future in the form of technology, while the poor experience the future in the form of calamity.

At its best, deep-time thinking contests the eschatologies of fundamentalism and the chaotic short-termism of so much present politics – foregrounding instead the rights of what Rebecca Solnit, writing of the climate-strikers, calls the “ghostly billions not yet born”. In our crisis epoch, it recognises that the continued survival of our species and others depends on just such a stretched perspective, rather than the crash-ended narrative arcs of disaster capitalism, or fetishised apocalypse dreams that foreclose action in preference for spectacle.

In The Great Derangement, Ghosh identifies three of the main challenges posed by the Anthropocene to literature and culture: how to represent unfoldings of action and consequence within deep time; how to recognise the aliveness of the more-than-human world (“other, fully aware eyes looking over our shoulders”); and how to come to terms with the profound decentring of human presence. Ghosh is especially interested in the realist novel’s adequacies in these respects, and he finds the form not only to have been rendered obsolete by circumstance, but complicitly to have engaged in what he calls the “concealment” of environmental breakdown. However, he writes hopefully, “new, hybrid forms will emerge – and the act of reading itself will change once again, as it has many times before.”

Such hybridity has long been at work in science fiction, of course; now it is happening in non-fiction too. New online magazines such as Emergence are redefining what an Anthropocene essay might look like and how it might be read. Experimental climate-change reportage such as Elizabeth Rush’s Rising; major environmental histories such as Floating Coast, Bathsheba Demuth’s study of the Bering Strait; Lauret Savoy’s brilliant account in Trace of deep time, race and the American landscape; and innovative print essays such as Emily Raboteau’s recent Climate Signs – all are recognising the poly-temporal weaves of culpability, vulnerability, elementality and urgency that characterise the present situation. “When readers turn to the art and literature of our time,” Ghosh writes, imagining a future reader gazing back at the cultures of the Anthropocene, “will they not look first and most urgently for traces and portents of the altered world of their inheritance?”

What started as a journey into pure matter became, to my surprise, an exploration of hidden human depths

Underland was composed in anticipation of that future reader’s scrutiny. It moves over its course from the dark matter formed at the universe’s birth (studied in a time projection chamber sunk beneath the Yorkshire moors) to the nuclear-waste futures of the Anthropocene (stored in an eternity chamber sunk beneath the Bothnian Sea). Underland’s first chapter is a descent, its last is a surfacing, and during the voyage of 4.6bn years made between those two remote points – crossing landscapes from the Mendip Hills to the Slovenian highlands, the Lofoten Islands to Greenland’s ice cap, and from western Finland to a Cambridge spinney a mile from my home, where nine springs rise from the bedrock chalk. What started as a journey into pure matter became, to my surprise, an exploration of hidden human depths, both wondrous and atrocious. We all carry underlands within us, but only rarely acknowledge their existence.

My wish was to answer Ghosh’s call for writing that might actively “unconceal” the traces of our fast-altering world: its untimely surfacings, its entombments, its visions of both darkness and light. The hope was to find a hybrid non-fiction form that might – by speaking both of the bright time of the lived human moment, and the more-than-human resonances of deeper times (ice time, tree time, species time, the giant, shifting lifetime of rock) – be at once ancient and urgent. While writing Underland I have come to think of claustrophobia as one of the distinctive experiences of the Anthropocene: a sense of time and space running out; of being in the grip of Earth forces triggered by human actions but exceeding human control; of feeling, in short – as the theorist Timothy Morton bluntly puts it – “stuck”.

Underland first surfaced into my mind while the Chilean miners were being rescued from the Mesozoic dark. I finished its final paragraphs in June last year, while the world was obsessed by another underland story that trembled on the brink between matter and myth – the disappearance into the cave-labyrinth under a mountain of the Thai footballers and their coach. Here, again, were the brutal presences of water, rock and weather. Here were fragile lives held in indifferent darkness. Here was the intervention of an arrogant man-god in the form of Elon Musk. Here, again, were bravery, love and quests into darkness in the hope of illumination. Here were echoes of countless prior underland stories, from the myth of the Minotaur, through Scots ballads of Thomas the Rhymer (taken “under the hill” by the Queen of Faery), to Inuit tales of glaciers engulfing and then releasing travellers. One of the marks by which the rescuers knew the boys were further into the flooded system was – of course – a handprint pressed into the mud of a chamber wall.

As I wrote towards my book’s end, so the story of the footballers unfolded towards its conclusion – opening out and spiralling down, at last, to the miraculous fact of children surfacing from inside the Earth, one by one, their parents embracing them as they wept tears of joy and relief, able at last to imagine the future again.

• This article was amended on 23 April 2019 to correct a misspelling of the family name of Bathsheba Demuth as Demouth. It was further amended on 1 May 2019 to correct a reference to John Playfair, whose first name we had given as James.

• Underland by Robert Macfarlane is published on 2 May by Hamish Hamilton (£20). To order a copy go to guardianbookshop.com or call 0330 333 6846. Free UK p&p over £15, online orders only. Phone orders min p&p of £1.99.