On the shores of Kamilo Point, in Hawaii, geologists have identified a new kind of stone. A sediment of recent history, the agglutinated rock displays milky-blue flecks, iotas of dull green, and fibrous orange twists. It is known, because of its unique properties, as “plastiglomerate.” That the name grinds together two familiar-sounding words is a clue to the stone’s qualities as an amalgam. What we are talking about is a rock veined not with metal or quartz, but with plastic. Plastiglomerate forms where polymer flotsam (trash, washed up on the tide line in this instance) is subject to high heat and melts, wrapping together particulate such as shell grit or sand. It then solidifies as it cools. Or, if liquefied plastic drips into hairline fissures in basalt or other porous minerals, what is left behind—a rock crazed with ersatz colors—can also be deemed plastiglomerate. Campfires are one source of that high heat. Plastiglomerate may also emerge along the scorched trail of a wildfire, or it might be cauterized into the ground by lava. It almost certainly appears in places where people burn their rubbish. Call it the birthstone of the age of unintended consequences.
Novel metals and mineraloids are everywhere today, not made by nature but engineered in the course of human industry. The bronze, brass, and pewter alloys of ancient times have been succeeded in the modern era by aluminum products (refined from bauxite), steel, industrial abrasives, synthetic gemstones, and laboratory-built crystals deployed widely in lasers. Plastiglomerate—neither natural nor fabricated, exactly—may represent the most direct conduit between our current consumer society and the far-flung future. This is how shopping enters the fossil record. Junk plastic tends to shatter or fray into filaments and specks, fine like a powder. (One of plastic’s most pernicious qualities is that it doesn’t so much decay as divide into smaller and smaller pieces.) Bonded to rock, plastic gains inertia and long-lasting cohesion; it gets gravity.
Researchers say that in all probability, plastiglomerate will be deposited into top-level strata, plasticizing the landscape itself. But the churning of the planet’s mantle could carry plastiglomerate steadily down, over centuries or longer, to form a seam of crushed consumables underground—as lurid as opal and as imperishable as ore. In cementing together two different types of matter—synthetic plastic and geochemical rubble—plastiglomerate also offers an object lesson in the melding of different timescales. The slumberous plane of rocks is characterized by its slow-motion weathering and its gradual, granular accretions. Geology does transform and flow, of course—the summit of Mount Everest is famously marine limestone—but short of major tectonic events like earthquakes and volcanic eruptions, changes in the mineral world are believed to happen over such protracted intervals that they prove almost imperceptible. By contrast, the preponderance of plastic refuse consists of lightweight packaging products, designed to be swiftly jettisoned and replaced. The irony is that, although the junk may not have been built to last, it could extend into a future well beyond individual human lifetimes, perhaps even beyond the recording of history. Folded into rock, plastic enters the time span of forces capable of elevating a seafloor into a mountain peak.
In Underland: A Deep Time Journey, the British writer Robert Macfarlane pursues the subsurface evidence of today’s major environmental changes, following what trickles down into the Earth and what migrates upward from beneath. This plunge beneath the planet’s topsoil into caves, catacombs, sinkholes, mines, meltwater moulins, and whirlpools opens new terrain to a naturalist whose adventures before now have soared skyward and reached outward. In Mountains of the Mind: A History of a Fascination (2003), Macfarlane gauged the compelling power of alpine ranges in history and culture. The Wild Places (2007) went on to survey invigorating myths of wilderness. Throughout The Old Ways: A Journey on Foot (2012), the author’s cerebral excursions into many different subjects (botany, architecture, literature, art) kept pace with his travels over public lands, along ancient pilgrimage trails and trading routes.
A mirror-world comes into focus in Underland, which quite literally fulfills Henry David Thoreau’s dictum that any topic worth exploring should be dug and cored headfirst. (“My head is hands and feet,” Thoreau wrote in Walden. “I feel all my best faculties concentrated in it. My instinct tells me that my head is an organ for burrowing, as some creatures use their snout and fore-paws.”) Underland tunnels into biology, history, physics, glaciology, and eco-poetry, among other specialties, as Macfarlane visits with scientists, archaeologists, explorers, and activists at different sites across the Northern Hemisphere. Yet the organizing force in this book turns out to be not freedom but claustrophobia.
Take the ruckle. Cute word; utterly terrifying reality. An underground subsidence of boulders, a ruckle resembles an oversize stash of marbles, prone to shifting and toppling. Its ingress is a route through chinks and cracks held open by the chancy fortune of geology’s distributed weight. In an early scene, Macfarlane, along with a fellow caver, enters a ruckle in the Mendips, a quarried limestone range in southwest England pocketed with burial chambers dating back 10 millennia. Any movement within the ruckle threatens to destabilize it, slamming the whole structure shut like a trap set by a long-forgotten god. At the entrance, Macfarlane identifies a nylon cord known to spelunkers as an “Ariadne’s thread” (after the ball of string Theseus deployed to navigate the Minotaur’s maze)—a line tacked in by earlier pathfinders that leads through the labyrinthine compressions. Macfarlane has to contort his body in the dark and lever himself, ever so delicately, against frigid rock faces to proceed. No, Robert, you think, let’s not.
I was still holding my breath, when, a page later, he submits to the metaphysical horror of arriving at the impassable narrowing of the ruckle—a bottleneck, a mentally asphyxiating socket in the rock. No one speaks. “Language is crushed,” Macfarlane writes. “We are anyway too busily engaged building structures within ourselves that might house our spirits.” To go underground is to be exposed both to physical risk and to mortal fears surfacing in one’s inner space—this trembling comes from within and without. Can it get worse? The men must summon the will to retrace their path through the boulders, never mislaying the thread that meanders toward the elusive, and ever more hallucinatory, sunlight above.
Of all the Earth’s terrestrial vertebrates, humans make the deepest incursions into the underground. The farthest that any animal, other than us, is known to burrow from the surface of the planet is 13 yards—the feat of, unbelievably, the Nile crocodile. Below this level live permanent troglodytes, organisms that never see the sunlight. Microbes and minuscule stygofauna—glassy snails, shrimplike creatures—bob in groundwater systems, and pale amphibians furl in the murkiest reaches of caves. A species of roundworm has been detected more than two miles belowground. Yet humans go even farther. Aided by excavating machines, people have delved to a record depth of 7.7 miles, straight into the rock off the Russian island of Sakhalin, and deeper (as far as we know) than the most cavernous marine trench.
Elsewhere, workers labor daily to extract gold that lies more than two miles underground. Macfarlane tours a potash mine with winding passages that reach from beneath the Yorkshire moors to far below the North Sea. If you think such depths are startling, consider the sheer number of holes humans dig. One estimate suggests that for every person alive, there may exist 21 feet of borehole hollowed out in pursuit of geothermal energy, and natural gas, oil, and other hydrocarbons. Even as human toil compiles new kinds of useful metals and crystals aboveground, it creates airy space where raw resources were once bestrewn below.
In conceiving of the long-term legacies of environmental change, we are perhaps more accustomed to thinking of the sky, the ocean, and the planet’s vegetated regions as locations where the damage is, and will be, conspicuously manifest. Atmospheric chemistry—modified by industrial, agricultural, and transportation emissions—begets climate breakdown. Deforestation, desertification, and sea-level rise are topographic, horizontal crises of land-clearing, creeping dunes, and saltwater surges. The realm of rocks, by contrast, seems too motionless and too recondite to be shaped by unnatural shifts above. Ashes to ashes, as they say; dust to dust. Everything reliably cycles back to the Earth.
Macfarlane’s significant contribution to an emerging canon of popular ecological writing is to articulate how the ground beneath our feet is not an immutable foundation, indifferent to human dominion. Far from it. Whether through the gouging work of multinational corporations, or as an insidious consequence of pollution (and the two are connected), the reach of human activity now extends, more pervasively than ever, into the mineral plane. The melting permafrost transforms a static, frozen tundra into something elastic and mushy, releasing puffs of noxious methane—a potent greenhouse gas. Widening cavities riddle the Arctic cryosphere. Cryolite, a mineral used to (among other things) add yellow to fireworks, has been mined into near-extinction. Falling water levels in a river in the Czech Republic reveal engraved “hunger stones” placed there to commemorate the worst droughts and starvations of the distant past. One stone reads: if you see me, weep.
What keeps coming up, everywhere, is evidence of our influence. The themes of captivity and claustrophobia point the reader toward Macfarlane’s overarching subject: how to live in a world of collapsing horizons. For much of Underland, we are made aware of existing inside a capricious nature that is, now more than ever, of human making. Standing on new and spiritless edge-lands exposed by retreating ice in Greenland, Macfarlane observes the uncanny symbolism of unwanted human omnipotence. Ice cores, a means by which scientists index climatic cycles, contain beads of air once captured between ancient snowflakes and then compressed into ice and layered ever deeper underground. Macfarlane sees each bubble as “a museum, a silver reliquary in which is kept a record of the atmosphere at the time the snow first fell.”
But the rate at which glacial ice is disappearing also puts us in touch with the realities of a heated future: What the ice communicates in Underland is as much about the decades and centuries to come as it is about the weather of the past. When a pyramid of ancient black ice, unpinned from the depths of a slushy fjord, explodes into Macfarlane’s view as he overlooks the terminus of the Knud Rasmussen Glacier, in Greenland, he calls it “this repulsive, exquisite thing,” an “obscenity”—alien, atavistic, and pivotal—that “should never have surfaced.” The question Did we do that? haunts the moment.
Subterranean environments are changing, Macfarlane shows, and the most enduring changes will carry on into distant time frames that are difficult, but necessary, to comprehend. Encounters with these exhuming and liquidating geological forces offer an opportunity to conceive of the “deep time” of the book’s subtitle—those durations that extend far beyond individual lifetimes and intergenerational lineages. “When you arrive at the very bottom, you will hear knocking from below,” wrote the Polish poet Stanisław Jerzy Lec. That aphorism echoes just beneath the surface throughout this book. Explorations in the underlands may inspire claustrophobia, and bring us into contact with the indelibility of human powers, but unexpectedly these spaces also refocus our attention on those who will inhabit the future—and how they will come to imagine us as they probe the traces we have left.
This article appears in the July 2019 print edition with the headline “The Earth’s Deepest Secrets.”