Acceleration, deceleration

Midway through his career-crowning text on the history of human fire use, Stephen Pyne presents a graph charting the course of two different kinds of combustion in the United States from the early twentieth century to the present.11Stephen Pyne, The Pyrocene: How We Created an Age of Fire and What Happens Next. Oakland: University of California Press, 2021 (e-book), fig. 3. The curve of fossil fuel emissions, unsurprisingly, climbs steadily upward. Though bumpier, the other curve—the total area annually burned by wildfire—descends as dramatically as its counterpart rises.

Relevant well beyond the US, the graph neatly captures the point Pyne has been making for over three decades: in the process of ascending to global climate-altering levels, anthropogenic combustion of fossil hydrocarbons has displaced another kind of fire. And the quenching of that other fire—the burning of living or recently living biomass—he argues, is just as significant as the unleashing of combustible matter from its lithic reservoirs. The monstrous fires that have erupted in recent years in Australia, California, the Mediterranean, and many other pyrophytic regions of the planet, Pyne insists, are evidence that substituting the closed fire of fossil-fueled heat engines for the open fire of landscape burning is utterly unsustainable.

Wildfire is photogenic, providing the visual and visceral appeal missing in so many other depictions of changing climate or shifting Earth systems. But this scintillating media presence conceals the fact that, despite escalating megafires, there is far less fire in the planetary landscape than there was half a millennium ago.22Stefan H. Doerr and Cristina Santín, “Global Trends in Wildfire and its Impacts: Perceptions versus Realities in a Changing World,” Philosophical Transactions of the Royal Society B, vol. 371 (2016). Overall, then, what we are witnessing is a deficit not an excess of burning biomass, or as Pyne puts it, the Earth now has “too much bad fire, too little good fire.”33Stephen Pyne, The Pyrocene, prologue.

Why might this be important for the identification of markers for the Anthropocene? Formalization of the hypothesis matters. But we shouldn’t forget the claim by its leading exponents that the Anthropocene “has the capacity to become the most politicized unit, by far, of the Geological Time Scales and therefore to take formal geological classification into uncharted waters.”44Jan Zalasiewicz, Mark Williams, Will Steffen, and Paul Crutzen, “The New World of the Anthropocene,” Environmental Science and Technology, vol. 44 (2010): p. 2,231. No less than the choice of a starting date, the selection of markers has potentially profound implications for how we understand, distribute, and reimagine human agency.

We should also recall that the question of a possible departure from Holocene conditions arose out of the relatively new field of Earth system science—prior to the turn to the more established discipline of geology for confirmation. The subsequent collaboration between the study of “hard rock” geology and the more mobile envelope of the outer Earth system may itself mark a significant juncture in the scientific understanding of how the Earth operates. As Zalasiewicz et al. explain, “geologists … benefit from this mutual exchange … as it enables better process models of the stratigraphical data,” while benefits to Earth System science accrue from “the recognition of geological signals as additional and proxies … especially for testing models and forecasting future scenarios.”55Jan Zalasiewicz, Will Steffen, Reinhold Leinfelder, et al., “Petrifying earth process: The stratigraphic imprint of key Earth System parameters in the Anthropocene,” Theory, Culture & Society, vol. 34, issues 2–3 (2017): p. 97. Consequently, the Anthropocene hypothesis may already be shifting the platform on which it seeks to ground itself.

Fire is an especially potent intermediary between the Earth system and the lithic strata, I want to suggest, and the human capture of fire is key to our species’ acquisition of geological agency.66Nigel Clark and Lauren Rickards, “An Anthropocene Species of Trouble? Negative Synergies between Earth System Change and Geological Destratification,” Anthropocene Review, (forthcoming). This brings us back to Pyne’s intersecting downward inflection of landscape burning and upward arc of fossil fuel combustion—curves that tellingly part company, at least in the US case, around 1950. By comparison with the “Great Acceleration” of fossil-fuel combustion, the “great deceleration” of landscape fire may be too discontinuous and difficult to disaggregate from other signals to be an independent contender for marking the Anthropocene. On the other hand, too hastily severing the ascent of fossil hydrocarbon combustion from the descent of landscape burning may well preemptively tease apart what Anthropocene science has so promisingly woven together.

This becomes even more pertinent when we consider the possible political repercussions of electing an Anthropocene marker. To date, the chosen markers foreground predominantly western technological developments, the rhetoric of “acceleration” itself mirroring the industrial capitalist axiomatic of continuous linear accumulation. In the process, other modes of inhabiting the Earth, in particular the use of techniques and practices that impact longitudinally rather than synchronously, risk being obscured.77See Matt Edgeworth, Erie C. Ellis, Philip Gibbard, Cath Neal, and Michael Ellis, “The chronostratigraphic method is unsuitable for determining the start of the Anthropocene,” Progress in Physical Geography: Earth and Environment, vol. 43 no. 3 (2019): pp. 334–44. This is particularly problematic in the case of nuclear testing, much of which took place in the unceded customary land, sea, and air of colonized peoples. Related risks attend highlighting the signatures of combusting fossil hydrocarbons, if treated in isolation. But if we at least attempt to address the decline of landscape burning in tandem with rising fossil fuel combustion, a deeper and much more shared history of cultural burning comes into relief.

In the following, extending Pyne’s notion of a “pyric transition” from open-field landscape burning to the chambered combustion of fossil biomass, I suggest how an expanded focus on fire not only weaves longitudinal and globally synchronous forms of human geological agency into one narrative, but also strengthens the conceptual convergence of the study of Earth systems and the lithic strata.

Fire as marker

Fire is the vernacular term for a rapid, positive feedback reaction that converts chemical energy into thermal energy. While some other astronomical bodies in our solar system have ingredients of fire, Earth is the only planet on which the necessary components of fuel, ignition source, and an oxidizing agent are fully integrated.88Pyne S, Fire: A Brief History. Seattle: University of Washington Press, 2001, p. 3.  Here, photosynthesizing life-forms turn sunlight into energy-rich carbon compounds, while fire reverses the equation by decomposing carbon-rich organic matter into thermal energy. The simple presence of life, however, is not enough. It took a planet-wide oxidation event, the rise of multicellular organisms, and the colonization of land by plants to finally fuse fire’s three ingredients, possibly beginning in the early Devonian.99Ibid. It took another hundred million years or so for the “fire planet” to evolve a creature capable of handling fire.

For most of the million or more years the extended human family has been manipulating fire, the impact has been localized, intermittent, and patchy. The proposal that anthropogenic fire-enabled deforestation deep in the Holocene helped defer the return of an ice age is contentious but has yet to be ruled out.1010A. Ganopolski, R. Winkelmann, and H. Schellnhuber, “Critical insolation–CO2 relation for diagnosing past and future glacial inception,” Nature, vol. 529 (2016): pp. 200–207. A stronger, early contender for the onset of planet-wide anthropic impact, initially favored by Anthropocene progenitor Paul Crutzen, was the take-off of fossil-fueled industrialization—“the thermo-industrial revolution of nineteenth century Western civilization.”1111Will Steffen, Jacques Grinevald, Paul Crutzen, and John McNeill, “The Anthropocene: Conceptual and historical perspectives,” Philosophical Transactions of the Royal Society A, vol. 369, no.1938 (2011): pp. 842–67, p. 847. As the demand for a pronounced geosynchronous signal turned attention to the post-World War II surge of globalization, it is the spheroidal carbonaceous particle (SCP) that has most clearly inherited and updated the “thermo-industrial” thematic.

A subset of fly ash—airborne particulate by-products of high-temperature fossil fuel combustion—SCPs are residues of the incomplete burning of pulverized coal or oil droplets.1212Neil L. Rose and Agnieszka Gałuszka, “Novel Materials as Particulates,” in The Anthropocene as a Geological Time Unit, ed. Jan Zalasiewicz, Colin N. Waters, Mark Williams, and Colin P. Summerhayes. Cambridge: Cambridge University Press, 2019, p. 51. While their microscopic size contributes to global atmospheric diffusion, SCPs also have the advantage of having no natural counterpart and thus being readily distinguishable in sedimentary samples. But in making a case for SCPs as an especially robust indicator of a mid-twentieth century Anthropocene onset, Neil Rose goes beyond emphasizing their ubiquity and convenience, stressing their link to a fundamental driver of anthropogenic global change: the combustion of fossil fuels.1313Neil L. Rose, “Spheroidal Carbonaceous Fly Ash Particles Provide a Globally Synchronous Stratigraphic Marker for the Anthropocene,” Environmental Science & Technology, vol. 49 (2015): p. 4,160.

In the bigger picture of Anthropocene science, this direct connection between the physical archive of the novel lithic strata and significant Earth system change seems to offer something lacking in the case of the proposed radionuclide marker—which for all the clarity of its signal has a much more ambiguous connection with human impact on Earth processes. However, if we step further step back, the shared, integrative force of fire begins to show up in other proposed markers. In one way or another, anthropogenic fire underpins rising atmospheric and oceanic CO₂ concentrations, the broader continuum of black carbon deposits, and proliferating human-made minerals such as concrete, alloyed metals, glass, ceramics, and plastics.

So we should also consider the significance of fire in early iterations of the idea that human activity might transform Earth processes in their entirety. In a 1982 paper, Crutzen conjectured that a nuclear exchange would result in massive wildfires generating photochemical smog that could “change the heat and radiative balance and dynamics of the earth and atmosphere” with devastating impact on surviving humans.1414Paul Crutzen, and John Birks, “The atmosphere after a nuclear war: twilight at noon,” Ambio, vol. 11 (1982): p. 123. More generally, fire came to play an integrative role in Crutzen’s vision of a dynamic and changeable Earth system. It’s also worth recalling his early efforts to distinguish between forms of combustion that added carbon to the atmosphere and those that returned carbon to the soil—notably the biomass burning of shifting cultivators.1515Wolfgang Seiler and Paul Crutzen, “Estimates of Gross and Net Fluxes of Carbon Between the Biosphere and the Atmosphere From Biomass Burning.” Climatic Change, vol. 2 (1980): pp. 207–247. As Crutzen and his coauthor later concluded in a collection that integrated the fields of wildland fire science and atmospheric chemistry: “the preservation and study of fire will assist humanity in its larger stewardship of the Earth.”1616Johann Goldammer and Paul Crutzen, “Fire in the Environment” in Fire in the Environment: The Ecological. Atmospheric, and Climatic Importance of Vegetation Fires. ed. Johann Goldammer and Paul Crutzen. Chichester: Wiley, 1993, p. 11.

Taking inspiration from both Pyne and Crutzen, I want to step back still further from the question of identifying an end-of-Holocene marker in order to dig deeper into the issue of how Anthropocene science can help us make sense of human planetary agency. Just as fire, over the last 400 million years, has played a vital part in the interactions between the relatively mobile envelop of the outer Earth system and the slower-moving fabric of the lithic strata, it is the capture of fire by humans, I suggest, that has enabled us to emerge as a particularly active hinge between these two planetary domains.

Human fire at the strata-Earth system juncture

Terrestrial fire is predominantly a surface phenomenon. Many organisms take advantage of fire—to open seeds, promote new growth, flush out prey—but only humans actively manipulate flame. More than an event in human history, Pyne insists, “the capture of fire by Homo marks a divide in the natural history of the Earth.”1717Stephen Pyne, “Maintaining Focus: An Introduction to Anthropogenic Fire,” Chemosphere, vol. 29, no. 5 (1994): p. 889. If skillful landscape burning has dramatically increased the range and niche of humans, however, so too has domesticated fire been the key to the human traversal of the Earth “vertically.”1818Nigel Clark “Vertical fire: For a pyropolitics of the subsurface,” Geoforum, vol. 127 (2021).

As diurnal, surface-dwelling creatures we need flame to light the way underground. It may not be coincidental that our distant ancestors look to have acquired the ability to handle fire in an environment where they also negotiated dynamic and fractured rock formations. East Africa’s Rift Valley—the largest, most long-lived, fracture zone on the Earth’s surface—is characterized by “complex tectonics and intense volcanism.”1919Geoffrey King and Geoff Bailey, “Tectonics and Human Evolution,” Antiquity, vol. 80 (2006): p. 277. Rift Valley topography was conducive to frequent patchy burning, while its constant volcanic activity supplemented lightning’s spark, and there has long been speculation that hominins first captured flame not from raging wildfire but from the more constant ebb of lava in their immediate environments.2020Nigel Clark, “Vertical fire.” There are also intriguing signs that having migrated away from ancestral volcanic homelands, ancestral humans learned to bury stones beneath hearth fires—using heat to transform available sedimentary rock so it acquired some of the flaking and sharpening properties of volcanic rock.2121Kyle Brown, Curtis Marean, Andy Herries, et al, “Fire as an Engineering Tool of Early Modern Humans,” Science, vol. 325 (2009): pp. 859–862. If this is the case, then already 70,000 years ago humans were using high heat to restructure inorganic matter—and in the process reconfiguring their relationships with the subsurface.

This fire-mediated articulation between the Earth’s surface and the rocky strata intensifies with the enclosure and intensification of flame. The earliest purpose-built fire containers—rudimentary kilns excavated at Dolní Věstonice—are estimated to be 26–30,000 years old.2222Pamela B. Vandiver, Olga Soffer, Bohuslav Klima, and Jiři Svoboda, “The origins of ceramic technology at Dolni Věstonice, Czechoslovakia,” Science, vol. 246 (1989): pp. 1002–1008. When the final Pleistocene glaciation ceded to warmer, steadier climates and some nomadic peoples settled into more sedentary lifestyles, chambered fire burgeoned into a vital constituent of Neolithic life. Ovens rendered grains digestible, and out of kilns came earthenware vessels, bricks, tiles, and later metals and glass.2323Theodore Wertime, “Pyrotechnology: man’s first industrial uses of fire,” American Scientist, vol. 61, no. 6 (1973): pp. 670–682.

The search for metallic ores drew us further into the depths of the Earth, and mining made new demands of fire. “Fire-setting”—exposure to high heat followed by quenching—was early miners’ chief means of cracking rock. “Prospectors burned over hillsides to expose rock” recounts Pyne; “Miners relied on fire to tunnel, to smelt, to forge.”2424Stephen Pyne, Fire, p. 131. As mining fed ores into the furnace, tools forged by metalworkers expediated extraction, and as demand for ores escalated, the drive and ability to extract these minerals correspondingly advanced. Again, we can see the enclosed fire of the artisanal furnace as a novel hinging together of mineral-bearing strata and Earth system fluxes.2525Nigel Clark, “Fiery Arts: Pyrotechnology and the Political Aesthetics of the Anthropocene,” GeoHumanities, vol. 1, no. 2 (2015): pp. 266–284. In the ancient Middle East, as archeologists document, there was a dynamic, self-reinforcing trade relationship between highland metallurgy and the intensive grain cultivation of the alluvial lowlands2626Leslie Aitchison, A History of Metals, Vol. 1. London: MacDonald & Evans, 1960, pp. 18–24.—or what we might view as a new articulation between sedimentary and metalliferous zones.

Although Pyne himself refers to the longer history of chambered fire, there is a sense in which 20,000-plus years of pyrotechnology complicates his more singular notion of a pyric transition between fossil-fueled heat engines and landscape burning. A further complication comes with the invention of another kind of fire: the positive-feedback biochemical reaction sped up to a split-second.

Over the course of extensive experimentation, researchers in ninth-century China pioneered a form of combustion in which the sudden release of pure oxygen accelerates the conversion of available fuel into hot gas in a few thousandths of a second. While the geological impact of escalating firepower has been noted, less attention has been given to understanding weaponized explosions as applications of a novel kind of fire.2727For the geological impact, see Mat Zalasiewicz and Jan Zalasiewicz, “Battle-scarred Earth: How war reshapes the planet,” New Scientist (2015): pp. 36–39.  Indeed, we might see near-instantaneous combustion as the first entirely new form of fire on Earth for over four hundred million years: a great acceleration of combustion that both anticipates and enables key aspects of the better-known post-World War II “Great Acceleration.”

Explosive gunpowder and its successors also have significant nonmilitary impacts on the mixing or turbation of rock fabrics. By the mid-nineteenth century, commercial applications of gunpowder for mining and civil engineering had overtaken military uses. As well as these direct geological impacts, ultra-high-speed combustion has indirect but momentous repercussions through the historical linkage between explosive weapons and the heat engines that powered industrialization. As Lewis Mumford observed in the 1930s, “the gun was the starting point of a new type of machine: it was, mechanically speaking, a one-cylinder internal combustion engine.”2828Lewis Mumford, Technics and Civilization. New York: Harcourt, Brace, 2010 (original 1934). p. 88.  Joseph Needham fills out this storyline—tracking a history of schemes and experiments to put gunpowder to useful work that go back to the sixteenth century. Scientist-inventor Christiaan Huygens’ project with the French Academy of Sciences in the 1670s is pivotal. As Huygens wrote: “The force of cannon powder has served hitherto only for very violent effects… people have long hoped that one could moderate this great speed and impetuosity to apply it to other uses.”2929Cited in Joseph Needham, Science and Civilisation in China: Vol.5. Cambridge: Cambridge University Press, 1986, p. 557.

Initially working under Huygens on the moteur à explosion, it was Denis Papin who recognized that steam power offered a “less violent” route to creating the vacuum that could drive a piston. Papin set research and development on a path towards external combustion—using fire-heated boilers as a motive force. Though not powered with gunpowder, the internally combusting moteur à explosion would be revived some two centuries later as the driving force of the automobile.3030Nigel Clark, “Infernal Machinery: Thermopolitics of the Explosion,” Culture Machine, vol. 17, (2019). The fossil-fueled automobile, in turn, would add its immense heft to the shifting relationship between the lithic strata and the Earth system—adding weight to the idea that a chain of pyric transitions lies behind successive transformations in the human capacity to hinge together the Earth system and the lithic strata.

Combustive justice and the Anthropocene

Following the “wide initial approach” to the Anthropocene, the demands of formalization call for the selection of a “primary” signal: a single reference point deputizing for the breadth of anthropogenic impacts on Earth processes and structures.3131On the “wide approach,” see Jan Zalasiewicz, Colin Waters, Colin Summerhayes et al, “The Working Group on the Anthropocene: Summary of Evidence and Interim Recommendations,” Anthropocene, vol. 19 (2017): p. 56. A careful, judicious framing is required if this obligation towards a certain reductiveness is not to be politically counterproductive. No less, care must be taken so that Anthropocene science’s most radical maneuver—its fusion of “hard rock,” deep time geology with Earth-system science—is not to be pushed into the background. In this final section, I make the case that a more explicit concern with the “integrative” thematic of human fire use could help us achieve both these aims at the same time.

There is great potential for the convergence of “stratigraphic” and Earth system thinking to open new perspectives on the way our species and its extended hominin family has gradually accrued its planet-altering agency. Such an approach, as I’ve been illustrating, helps us to see how the diverse setting-to-work of fire has played a key role in human intervention in the flows and cycles of the Earth system, in their traversal of lithic strata, and in their hinging together of these two planetary domains. If fire, as Pyne insists, integrates different environmental processes, so too might we say that it articulates between the major structural divisions of the Earth.3232 Stephen Pyne, The Pyrocene, prologue.

Indeed, we might push this idea further. As Earth system scientists remind us, “the planet Earth is really comprised of two systems—the surface Earth system that supports life, and the great bulk of the inner Earth underneath.”3333Tim Lenton, Earth System Science: A Very Short Introduction. Oxford: Oxford University Press, 2016, p. 17. Through the containment and intensification of fire, the genus that emerged in and around volcanically active Rift Valley has learned to reproduce some of the forces of the inner Earth. Already by 6,000 BP, high-heat artisans were stoking their furnaces to 1200-1300°C degrees—a temperature that approximates the maximum heat of lava.3434J. E. Rehder, The Mastery and Uses of Fire in Antiquity. Montreal: McGill-Queens University Press, 2000, p. 54. By using their kilns to melt and recrystallize rock, to metamorphosize minerals, to decompose and concentrate metallic ores, they effectively enfolded some of the power of the subcrustal Earth into the everyday spaces of their villages and towns.3535Nigel Clark, “Vertical fire.”

Later, with the weaponizing of gunpowder into explosive devices, Chinese military engineers set in play a mobilization of matter so rapid that it overtook even the 200–300 meters per second velocity of rocks ejected during volcanic explosions.3636Gary Settles, “High-speed Imaging of Shock Waves, Explosions and Gunshots,” American Scientist, 2006: https://www.americanscientist.org/article/high-speed-imaging-of-shock-waves-explosions-and-gunshots. If this new fire dramatically accelerated the exchange between the Earth system and strata, it also played a preparatory role for the thermonuclear explosion—which in a certain sense domesticates the nuclear fusion processes that power stars such as our own sun. In this regard, the fiery explosion can be seen as a step toward another kind of hinging together between systems—this time terrestrial and cosmic: a point that might be extended towards rocket propulsion and ability to leave the Earth’s orbit.

Whether by way of fire or other elemental processes, I am suggesting, new framings of the strata-Earth system interface help us to understand how humans acquired planetary agency. But this is also a matter of justice. It is an issue of acknowledging the multiple ways that different human collectives—throughout history and across the globe—have engaged with a dynamic, richly-resourced planet, and a question of confronting the suppression and marginalization these traditions have so often faced.3737Nigel Clark and Bronislaw Szerszynski, Planetary Social Thought: The Anthropocene Challenge to the Social Sciences. Cambridge: Polity Press, 2021. Just as researchers talk about a “black carbon continuum” in reference to the many ways that human agents generate residues from combustion, so too do we need to think of a broader continuum in which all extant human populations and many of our hominin ancestors played a significant role in learning how to negotiate planetary variability using fire and other forces.3838On the “black carbon continuum,” see Neil L. Rose and Agnieszka Gałuszka, “Novel Materials as Particulates,” p 52.

Whereas focusing on a radionuclide signature may be clear and “unambiguous” in important regards, it also risks masking the agency of Aboriginal Australians, Pacific Islanders, Kazakhs, and others on whose customary lands weapons testing so often took place. In the case of Indigenous Australians, this could occlude tens of thousands of years of shaping an entire continent through skilled application of fire to living ecosystems—in this way risking a return to the racist imaginary of “primitive” people on the receiving end of unfathomable Western technological supremacy.3939See Marcia Langton, Burning Questions: Emerging Environmental Issues for Indigenous Peoples in Northern Australia. Darwin: Northern Territory University, 1998.

Conversely, addressing a continuum of pyrogenic impacts that treats the signature of marginalized and ascendant practices as two sides of a definitive, shared anthropic attribute might signpost a greater willingness “to take formal geological classification into uncharted waters.” But pursuing combustive justice is not simply a question of ceding objectivity to political imperatives. It is also about directing scientific attention towards processes that have emerged and developed over thousands, or even hundreds of thousands of years: a matter of digging beneath comparatively shallow stratigraphic signatures to unearth their more profound conditions of possibility. We may well learn some valuable lessons by registering the traces of nuclear test ban treaties. But only by exploring the deep, complex, and tangled human history of intervening in elemental processes will we gain an appreciation—or reappreciation—of alternative possibilities for joining forces with the Earth.

Nigel Clark is Chair of Human Geography at the Lancaster Environment Centre, Lancaster University, UK. He is the author of Inhuman Nature (2011) and (with Bronislaw Szerszynski) Planetary Social Thought: The Anthropocene Challenge to the Social Sciences (2021).

Please cite as: Clark, N (2022) Anthropogenic Fire as the Hinge between Earth System and Strata. In: Rosol C and Rispoli G (eds) Anthropogenic Markers: Stratigraphy and Context, Anthropocene Curriculum. Berlin: Max Planck Institute for the History of Science. DOI: 10.58049/sneg-r095