Underland: A Deep Time Journey

by Robert Macfarlane

The same three tasks recur across cultures and epochs: to shelter what is precious, to yield what is valuable, and to dispose of what is harmful. Shelter (memories, precious matter, messages, fragile lives). Yield (information, wealth, metaphors, minerals, visions). Dispose (waste, trauma, poison, secrets). Into the underland we have long placed that which we fear and wish to lose, and that which we love and wish to save.

I have rarely felt as far from the human realm as when only ten yards below it, caught in the shining jaws of a limestone bedding plane first formed on the floor of an ancient sea.

A long cultural history of abhorrence exists around underground spaces, associating them with ‘the awful darkness inside the world’, in Cormac McCarthy’s phrase.

We are presently living through the Anthropocene, an epoch of immense and often frightening change at a planetary scale, in which ‘crisis’ exists not as an ever-deferred future apocalypse but rather as an ongoing occurrence experienced most severely by the most vulnerable. Time is profoundly out of joint – and so is place. Things that should have stayed buried are rising up unbidden.

‘Deep time’ is the chronology of the underland. Deep time is the dizzying expanses of Earth history that stretch away from the present moment. Deep time is measured in units that humble the human instant: epochs and aeons, instead of minutes and years. Deep time is kept by stone, ice, stalactites, seabed sediments and the drift of tectonic plates. Deep time opens into the future as well as the past. The Earth will fall dark when the sun exhausts its fuel in around 5 billion years. We stand with our toes, as well as our heels, on a brink.

A flat ontology entices: all life is equally insignificant in the face of eventual ruin. The extinction of a species or an ecosystem scarcely matters in the context of the planet’s cycles of erosion and repair.

What these narratives all suggest is something seemingly paradoxical: that darkness might be a medium of vision, and that descent may be a movement towards revelation rather than deprivation.

Underland is a story of journeys into darkness, and of descents made in search of knowledge. It moves over its course from the dark matter formed at the universe’s birth to the nuclear futures of an Anthropocene-to-come. During the deep time voyage undertaken between those two remote points, the line about which the telling folds is the ever-moving present. Across its chapters, in keeping with its subject, extends a subsurface network of echoes, patterns and connections.

The human bodies, it will later be established, are more than ten millennia old, and among them are children and infants as well as adults. All show signs of chronic malnutrition. The adults stood little more than five feet tall. The children’s molars were scarcely worn. Slowly, it becomes clear to those who study this mysterious place – now known as Aveline’s Hole – that, far back in the Mesolithic, the cave was used as a cemetery over a period of around a century.

We are often more tender to the dead than to the living, though it is the living who need our tenderness most.

The first fact of limestone is its solubility in water. Rain absorbs carbon dioxide from the air, creating a mild carbonic acid – just sharp enough to etch and fret limestone, given time. This fretwork deepens into limestone’s surface perforations of gryke and clint, and also its hidden labyrinths of rift and chamber. Streams shape stone with their energy.

‘I didn’t understand the Mendips until I began to explore them from below,’ Sean says. ‘Almost everything here involves the underworld somehow: quarrying, mining, caving. Bronze Age lead mining. Coal mining by the Romans. Quarries for limestone grit, so big they have a spiral ramp cut to a narrow core, in order that the lorries can get up and down, like an industrial version of Dante’s descent in The Inferno. And basalt quarries to supply hardcore for top-dressing roads.’

We are, certainly, a burying species as well as a building species – and our predecessors were buriers too. In a cave system called Rising Star in the limestone of South Africa a team of palaeoarchaeologists led by six women has discovered fossilized bone fragments thought to belong to a previously unknown early human relative, a species now named as Homo naledi. The disposition of this dark matter in two deep-set chambers suggests, remarkably, that Homo naledi was already interring its dead underground some 300,000 years ago.

Limestone, in particular, has long been a geology of burial – in part because it is so common globally, in part because its erosive tendencies create so many natural crypts into which bodies may be laid, and in part because limestone is itself, geologically speaking, a cemetery. Limestone is usually formed of the compressed bodies of marine organisms – crinoids and coccolithophores, ammonites, belemnites and foraminifera – that died in waters of ancient seas and then settled in their trillions on those seabeds.

Flowstone is the name given to the calcite deposits that precipitate out of minerally saturated water as it runs over the slopes of limestone caves. You might imagine flowstone as a kind of white candle wax, gradually hardening as it runs, though it is built up over spans of time rather than by brief incandescence. Because of the gradual nature of its formation, flowstone sets into elaborate ruches and folds – elephant-skin gathers of texture, wrinkled stockings. Flowstone is very beautiful to look at and very hard to grip.

A ruckle is a group of boulders that have caved against one another, blocking a section of passage, but through the gaps of which a path might just be traced. Ruckles are delicate, unpredictable structures. Without disturbance, a ruckle might hold its position for tens of thousands of years. But an earth tremor might shake it into a new order in an instant.

This is a bedding plane, formed when the rock was being laid down as sediment on a seabed. Strata movement has prised the sides of the plane apart millions of years later, water has worked to burnish an absence between them, and our onwards route is into this deep time space, this deep time vice.

knowing for those few moments that to understand light you need first to have been buried in the deep-down dark.

The young physicist is searching for evidence of the shadowy presence at the heart of the universe: a presence so mysterious that it has thus far engulfed almost all of our attempts either to investigate or to represent it. The name we have given to this presence – which refuses to interact with light, which may not even exist – is ‘dark matter’.

It is a paradox of his work that in order to watch the stars he must descend far from the sun. Sometimes in the darkness you can see more clearly.

It is now known, for instance, that dark matter affects the rotation curves of spiral galaxies, causing all bodies within such a galaxy to revolve at comparable rates, regardless of their distance from the galaxy’s gravitational centre. It is also known that dark matter bends light as it passes around a galaxy, causing what is referred to as ‘gravitational lensing’.

What these observations and others like them suggest is that only around 5 per cent of the universe’s mass is made of the matter we can touch with our hands and witness with our eyes and instruments. This is the matter of stone, water, bone, metal and brain, the matter of which the ammoniacal storms of Jupiter and the rubble rings of Saturn are made. Astronomers call this ‘baryonic matter’, because the overwhelming share of its mass is due to protons and neutrons, known to physicists as ‘baryons’. A little over 68 per cent of the universe’s mass is presumed to be made of ‘dark energy’, an enigmatic force that seems to be accelerating the ongoing expansion of the cosmos. And the remaining missing 27 per cent of the universe’s mass is thought to be made up of dark matter – the particles of which almost wholly refuse to interact with baryonic matter.

Presently, the particle thought most likely to be the constituent of dark matter is known wryly as a WIMP – a weakly interacting massive particle. What we know of WIMPs suggests that they are heavy (up to more than a thousand times the weight of a proton),

scant regard for the world of baryonic matter. WIMPs traverse our livers, skulls and guts in their trillions each second. Neutrinos fly through the Earth’s crust, mantle and solid iron-nickel core without touching a single atom as they go.

Subterranean laboratories have been established around the world, dedicated to the detection of evidence that a WIMP or a neutrino has briefly interacted with baryonic matter. The experiments under way in these deep-sunk laboratories are all forms of ghost hunting, and they are located far underground because the surrounding rock shields the experiments from what physicists call ‘noise’. Noise is the trundle of everyday particles through the air, the din of the ordinary atomic world going about its business. Radioactivity is deafening noise. Cosmic-ray muons are noise.

DRIFT: directional recoil identification from tracks.

Salt has very low gamma radiation. Salt is a good insulator. Salt is radio-pure. Salt is an excellent substance in which to encase yourself if you want to study weakly interacting massive particles. But salt is also highly plastic. Salt flows over time. It creeps around. It sags. If you cut a chamber out of a seam of halite with 3,000 feet of bedrock above it, that chamber will slowly distort. The ceiling will dip, the sides will bulge. Gravity wants that space back. So the scientists working in the Boulby laboratory know they are operating in a temporary zone, with limited years of safe life. Deep time must be studied fast.

Another investigates a technology known as ‘muon tomography’, which makes use of highly penetrating charged particles (muons) produced by cosmic rays from space. Because of their ability to pass deep into rock, muons allow sunken structures such as the interiors of volcanoes and the hollow hearts of pyramids to be perceived. Muons offer a way of seeing through stone.

‘Imagine watching a game of billiards in which the red balls are visible but the white isn’t. Suddenly you see the red ball – an electron – move across the baize. By plotting the red ball’s path, you might be able to backtrack, as it were, the path of the invisible white ball – the WIMP – that struck it. And from this, you might be able to learn more about the direction, mass and qualities of that white ball. We’re looking to do this enough times, and with enough precision, to provide the signature of a dark-matter halo.’

If we’re not exploring, we’re not doing anything. We’re just waiting.’

‘At the weekends,’ Christopher says, ‘when I’m out for a walk with my wife, along the cliff tops near here, on a sunny day, I know our bodies are wide-meshed nets, and that the cliffs we’re walking on are nets too, and sometimes it seems, yes, as miraculous as if in our everyday world we suddenly found ourselves walking on water, or air. And I wonder what it must be like, sometimes, not to know that.’ He pauses, and it is clear that he is thinking now beyond the confines of the salt cavern, beyond even the known limits of the universe. ‘But mostly, and in several ways, I’m amazed I’m able to hold the hand of the person I love.’

As the Pleistocene was defined by the action of ice, and the Holocene by a period of relative climatic stability allowing the flourishing of life, so the Anthropocene is seen to be defined by the action of anthropos: human beings, shaping the Earth at a global scale.

Among the baselines considered by the group have been the first use of fire by hominins around 1.8 million years ago, the start of agriculture around 8,000 years ago, the Industrial Revolution, and the so-called ‘Great Acceleration’ of the mid twentieth century, when the nuclear age dawned, massive increases occurred in terms of resource extraction, population growth, carbon emissions, species invasions and extinctions, and when the production and discard of metals, concrete and plastics boomed.

A nitrogen spike, indicated in ice-cores and sediments, will be one of the key chemical insignias of the Anthropocene, caused by the mass global use of synthetic nitrogen-rich fertilizers and by fossil-fuel burning.

We all carry trace fossils within us – the marks that the dead and the missed leave behind. Handwriting on an envelope; the wear on a wooden step left by footfall; the memory of a familiar gesture by someone gone, repeated so often it has worn its own groove in both air and mind: these are trace fossils too. Sometimes, in fact, all that is left behind by loss is trace – and sometimes empty volume can be easier to hold in the heart than presence itself.

Then he told me about new research he had recently read concerning the interrelations of trees: how, when one of their number was sickening or under stress, they could share nutrients by means of an underground system that conjoined their roots beneath the soil, thereby sometimes nursing the sick tree back to health. It was a measure of my friend’s generosity of spirit that – so close to death himself – he could speak unjealously of this phenomenon of healing.

In the language of forestry and forest ecology, the ‘understorey’ is the name given to the life that exists between the forest floor and the tree canopy: the fungi, mosses, lichens, bushes and saplings that thrive and compete in this mid-zone. Metaphorically, though, the ‘understorey’ is also the sum of the entangled, ever-growing narratives, histories, ideas and words that interweave to give a wood or forest its diverse life in culture.

In the case of the tree–fungi mutualism, the fungi siphon off carbon that has been produced in the form of glucose by the trees during photosynthesis, by means of chlorophyll that the fungi do not possess. In turn, the trees obtain nutrients such as phosphorus and nitrogen that the fungi have acquired from the soil through which they grow, by means of enzymes that the trees lack.

Pollarding – the pruning of the upper branches of a tree to promote dense growth – keeps trees alive for longer, indeed can enter them into an almost indefinite fairy-tale time of longevity.

‘crown shyness’, whereby individual forest trees respect each other’s space, leaving slender running gaps between the end of one tree’s outermost leaves and the start of another’s.

I think of good love as something that roots, not rots, over time,

‘This is our problem when it comes to studying the fungal network,’ he says. ‘Soil is fantastically impenetrable to experiments, and the fungal hyphae are on the whole too thin to see with the naked eye. That’s the main reason it’s taken us so long to work out the wood wide web’s existence, and to discern what it’s doing.’

Just a few inches of soil is enough to keep startling secrets, hold astonishing cargo: an eighth of the world’s total biomass comprises bacteria that live below ground, and a further quarter is of fungal origin.

Scientists working in Chernobyl after the disaster there were surprised to discover fine threads of melanized fungi lacing the distressed concrete of the reactor itself, where radiation levels were over 500 times higher than in the normal environment. They were even more surprised to work out that the fungi were actively thriving due to the high levels of ionizing radiation: that they benefited from this usually lethal gale, increasing their biomass by processing it in some way.

There was also ‘the Lightning Guy’, who studied the effects of lightning strikes on below-ground ecologies, and tried to induce site-specific strikes by firing crossbow bolts trailing copper wire at storm clouds.

Mycohets are plants that lack chlorophyll and thus are unable to photosynthesize. As such they are entirely reliant on the fungal network for their provision of carbon.

‘I have this plan,’ Merlin says, ‘that for each formal scientific paper I ever publish I will also write its dark twin, its underground mirror-piece – the true story of how the data for that cool, tidy hypothesis-evidence-proof paper actually got acquired. I want to write about the happenstance and the shaved bumblebees and the pissing monkeys and the drunken conversations and the fuck-ups that actually bring science into being. This is the frothy, mad network that underlies and interconnects all scientific knowledge – but about which we so rarely say anything.’

According to the ‘free-market’ model, the connected forest is to be understood as a competitive system, in which all entities act out of self-interest within a cost-benefit framework, regulating one another by means of ‘sanction and reward’ systems. According to the ‘socialist’ model, by contrast, trees act as carers to one another, sharing resources through the fungal network, with the well-off supporting the needy.

To me, walking through a wood is like taking a tiny part in a mystery play run across multiple timescales.’

She is passionate about the catacombs, especially about preserving and documenting their swiftly changing features through photography and record-keeping.