Concrete: A Stratigraphic Marker for the Anthropocene
We are live in room number 2022 of the venerable International Court of Stratigraphic Arbitration where two esteemed scholars—an archaeologist and an anthropologist—appeared before the jury. On trial is the question whether concrete, the unparalleled material, is indeed an admissible marker for defining the onset of the Anthropocene. Here is a record of the first day of the hearing.
Introduction
Here, by decree of the organizers of this honorable Anthropogenic Markers project, the defending and prosecuting counsels will present to you, members of the Anthropocene Working Group (AWG) jury, the respective cases for and against using concrete as a key stratigraphic marker for the Anthropocene epoch.1
In the first section, the defense will introduce a list of points in favor of using concrete for this purpose. In the second section, the prosecution will present the arguments against it. If this seems the wrong way round, that is because the unprecedented conditions of Earth system change taking place today require us to consider adjusting normal procedures for deciding such things. This court is unusual in another sense. Traditionally, the cases for and against are opposed to each other: juries have to decide by majority vote which one is true and which one is false, with no gray area between. But nothing is quite that simple any more.
The third section will invite the jury to extend the debate beyond its currently set parameters, challenging the assumption that the Anthropocene must be thought of as a formal unit of the geological time scale, with a distinctive start date to be defined irrefutably in this court by means of a single, global, and isochronous anthropogenic timeline.2
The case for the defense: Arguments for concrete as marker of the proposed Anthropocene epoch
Exhibit 1 (Case for the Defense): The picture depicts the sedimentation of a layer of concrete, along with geological agents responsible for its deposition. The typical bodily gestures associated with pouring and raking concrete are reproduced every day by countless construction workers worldwide. You can almost feel the viscosity and graininess of it, the material resistance registered in the muscles of the arms and shoulders and back of the legs. The outcome of that effort in this case will be a smooth road surface for automobiles to travel on. Photo by Cristián Simonetti
1. Unparalleled scale and impact of concrete. The role of concrete in the emergence of humans as a leading geological force, capable of altering Earth history irreversibly, is undeniable. No other anthropogenic marker for the Anthropocene currently being debated by the AWG equals the sheer scale of concrete production and consumption.3 Concrete is by far the most abundant anthropic material ever created in Earth history. It extends upward in the form of skyscrapers, downward as the linings of deep shafts and tunnels, and laterally in the shape of roads and other laid horizontal surfaces. Taken globally, concrete infrastructure could be regarded as the largest composite artifact in human history. Humans have poured enough concrete to cover the entire surface of the globe with several millimeters of the material, though its actual distribution is patchy and uneven. Some is recycled, but much will end up in the stratigraphic record—where it can already be found in abundance—with potential for long-term survival on geological timescales. Concrete is also a significant contributor to global warming. Cement production alone is responsible for between 6 and 8 percent of global carbon emission, as one kilogram of cement amounts to roughly one kilogram of CO2. If the entire industry surrounding concrete production were to be considered as a single country, it would be the third largest CO2 emitter globally, only after the US and China.
2. Concrete as a matter of modernity. Concrete materializes—like no other anthropogenic marker—modern ideas of progress and human exceptionalism. It creates a solid platform for the enactment of social life that smothers and suffocates the growth of organic life below, while preventing the seeping of life-giving rain from above into the soil over large parts of Earth’s surface. Walking on such a platform is to inhabit the present that modernity has proclaimed for itself, sometimes styled as the end of history. Moving off such a platform allows city dwellers to temporarily step outside the condition of modernity and “reconnect with nature.” Paradoxically, the practices of workers engaged in extending the concrete platform (comprising familiar gestures and bodily movements associated with the mixing and laying of concrete, such as troweling and operating concrete-laying or concrete-spraying machinery) simultaneously remove the traces of those very practices, effectively smoothing them away (please refer to Exhibit 1): a routine act of erasure disturbed when random passers-by leave their mark on history by introducing a hand- or footprint or inscribing graffiti in the still hardening mix. Concrete—a moldable artificial rock—belongs simultaneously to geology and sociology, as it sets in stone the movements of modern history. It is the substance of a true—and, by far, the largest—geosocial formation.4
3. Concrete as shaper of human actions and gestures. According to the twentieth-century archaeologist and anthropologist André Leroi-Gourhan, technology evolved through the “exteriorization” of human gestures.5 Concrete infrastructure condenses like no other material the embodied gestures of modernity and teaches every new generation how to feel and think about the place modern humans occupy in Earth history. Indeed, the smooth surfaces of concrete infrastructure on which more than half the world’s population currently lives affords a particular way of walking that remarkably resembles the image of the flâneur, a character philosopher Walter Benjamin famously identified as distinctive of modern life and who others have remarkably described as “cast in concrete.”6 Sauntering on the smooth urban ground, a terrain devoid of obstacles and irregularities, the city stroller enjoys the spectacle of social life, irrespective of the deeper social and environmental history that has been materially erased, leveled, or covered over.
4. Concrete as present and future technofossil. For geologist and former chair of the AWG Jan Zalasiewicz, defining the Anthropocene involves an act of science fiction,7 in that geologists need to envision the condition of the stratigraphic record millions of years into the future, long after humans have disappeared and the remains of human activity have been sedimented in strata. Thus, for many stratigraphers, the Anthropocene is not regarded as strictly speaking a present reality, at least in a stratigraphic sense: rather it is considered to constitute a future past—a past as seen from the future imagined from the present. Concrete pulls us back from that speculative future to the Anthropocene as a present stratigraphic reality.8 It clearly does belong to a future past in the sense that concrete is likely to be preserved as a technofossil over geological timescales. But it can also be regarded as a technofossil now, as part of the present past. Concrete manufacture through technological process can itself be regarded as a kind of artificial fossilization, in which humans speed up the rock formation cycle. Instead of ancient seabeds containing the fossilized remains of once living creatures being hardened into stone through long processes of mineralization over millions of years, various materials are rapidly reconstituted inside kilns to produce cement through the application of intense heat, in what resembles a volcanic or igneous process,9 though humanly contrived. Subsequently, when added to water, sand, and aggregate and laid on the ground, concrete creates new strata, adding to what is, in the eyes of leading members of the AWG, now “the most abundant anthropogenic sedimentary rock on the planet.”10 Accordingly, concrete belongs from the start to solid geology. It already exists as a technofossil today, as its passage from technosphere to lithosphere is instant and direct. Concrete thus requires no science fiction imagination and no period of waiting for long-term petrification processes to take place underground in order for it to be used as a stratigraphic marker of the Anthropocene.11
5. Concrete as proxy for the “Great Acceleration.” Although concrete has existed and been deposited in the stratigraphic record since classical times, the larger proportion of it has been poured after portland cement was rediscovered and patented by Joseph Aspdin in 1824, during the Industrial Revolution, and mostly after the Second World War. This timeline corresponds to that of the so-called Great Acceleration, which describes simultaneous surges in growth rates across numerous measures of human impact on the Earth system.12
6. Concrete as testimony of environmental responsibility. Selecting an anthropogenic marker for the Anthropocene carries connotations with regard to who is responsible for the environmental crisis. Concrete, more than all other potential anthropogenic markers for the Anthropocene, provides a global material record of environmental responsibility that is at least partially available to all inhabitants of this planet with access to the internet, through open tools such as Google Earth. Concrete production and consumption—led traditionally by large economies of the global north, particularly the US and Europe, and followed more recently by emerging superpowers such as China and India—correlates well with global development indicators.
7. Concrete as proxy for the Anthropocene epoch. A recent study of artificial ground in London used the presence of concrete together with that of other anthropogenic materials to distinguish between Anthropocene and pre-Anthropocene layers.13 If the findings of the study are accepted, it would have major implications as to whether it is possible to locate the Anthropocene’s start as an actual stratigraphic boundary in the ground.
The case for the prosecution: Arguments against concrete as marker of the proposed Anthropocene epoch
Exhibit 2 (Case for the Prosecution): Construction of Rome’s metro line B, opened in the 1950s. The tunnel is comprised mostly of pre-cast concrete slabs. Towering above is the Colosseum, constructed two thousand years earlier on a massive concrete foundation 6 meters deep. In the background is a fourth century CE triumphal arch, built of brick-faced concrete revetted with marble. Recent excavations in the shadow of the Colosseum, in a concrete-lined shaft for the much deeper metro line C, found floors of Roman concrete under more than 12m of archaeosphere deposits. Photo from the-colosseum.net, public domain
1. Concrete as diachronous stratigraphic signal. Despite the points outlined by the defense, an argument persists against using concrete to mark a geological epoch (or indeed any time unit whose start must be precisely defined). To put it bluntly, there is a lack of fit between the diachronous signal presented by concrete (and other novel materials such as ceramic, brick, glass, plastics) on the one hand, and the imposition of an isochronous timeline, no matter where in time it is placed, on the other. The stratigraphic signature of concrete is spread out through time. The insistence on defining a precise start derives not from the evidence of strata but from the understanding of the Anthropocene as a division of the geological time scale, in this case as an epoch, requiring a globally isochronous timeline to separate it from the Holocene. If only stratigraphic evidence were used as the basis for understanding, the Anthropocene would be conceptualized as having diachronous beginnings, and accordingly would be classified as a time-transgressive time unit such as a biozone or event rather than an epoch.14 This assessment is in keeping with what historian Dipesh Chakrabarty describes from a historical viewpoint as “the plural beginnings” of the Anthropocene.15
2. The ancient origin and development of concrete For all the associations concrete has with modernity, and acknowledging that most concrete has been produced since the middle of the twentieth century (a point emphasized in the case for the defense), much concrete was also made and deposited in the ground before that time, certainly in the earlier part of that century and in the later part of the nineteenth century. Furthermore, concrete was extensively manufactured and used in ancient times. Roman cement (opus caementicium) was deployed extensively by the Romans for 700 years, forming part of many famous buildings, such as the Colosseum and the Pantheon, as well as routinely used in the construction of roads and ordinary buildings across the empire. By adding pyroclastic or volcanic materials to the mix, Romans developed a form of concrete that could set underwater and was resistant to seawater erosion. Many Roman concrete structures survive to this day, most buried underground or submerged underwater, but occasionally still standing above ground; please refer to Exhibit 2. Archaeologists often find concrete as surfaces, as parts of structures, and as inclusions in strata dated to the Roman period.
3. Co-occurrence of ancient and modern concrete in the same stratigraphic sequences. Where Roman forts and cities developed into major cities such as Vienna and London, it is common to find early and modern concrete deposits in single stratigraphic successions of anthropogenic ground, the former underlying the latter. This problematizes the use of concrete as a marker for the Anthropocene epoch, if held to begin in the mid-twentieth century. Of course, modern concrete can generally be distinguished from ancient concrete by its material composition and geochemical signal. But the category of “modern concrete” (like that of “ancient concrete”) is itself a heterogeneous one. It consists of a whole range of mixtures of constituent materials. Some of it even emulates Roman concrete through the addition of volcanic ash. That is, there is no single “modern concrete.” If using it as a marker for a mid-twentieth-century Anthropocene start, one would furthermore also have to distinguish between post-1950 concrete and pre-1950 concrete of the nineteenth and early twentieth centuries.
4. Potential for distortion of stratigraphic evidence. There are very few papers that actually look for concrete in strata. One that does is “Quantifying Anthropogenic Modification of the Shallow Geosphere in Central London, UK,” by R. L. Terrington et al.16 Despite the fact that concrete is typically regarded as only as a secondary marker of the Anthropocene, in this paper it is used as a primary stratigraphic marker, along with other anthropogenic materials, to distinguish between Anthropocene layers and pre-Anthropocene layers. Terrington et al. take material identified as rubble of bombed buildings to correspond roughly to the early 1940s Blitz over a large area of London. While there are parts of outer London where war rubble was deliberately dumped on the ground surface to fill in hollows and marshy ground, this does not apply to most of the heavily bombed residential areas from which rubble was cleared. The study assumes that “if coal and concrete are present, it is taken to be most likely an Anthropocene (post-Second World War) deposit as this coincides with the main interval of concrete production and usage.”17 On that basis, a considerable depth of anthropogenic ground is designated as dating to the Anthropocene. However, what the authors of the study fail to realize is that much of the area investigated is characterized by an abundance of rubble-filled cellars dating to the late nineteenth century, some of which were filled with later bomb rubble, but many of which used concrete as well as brick in their construction and were originally used for storing coal. The study ignores the complexity of stratigraphic successions of which such cellars are part, reducing these to a single layer supposedly dating to the Anthropocene. The idea that one can distinguish between Anthropocene and pre-Anthropocene layers in such complicated stratigraphic sequences from crude borehole data alone is seriously mistaken. The example illustrates the dangers of imposing a pre-specified isochronous timeline on the diachronous stratigraphic signal of concrete and other novel materials, and on the complex relational stratigraphic structure that is anthropogenic ground.
The case for convergence of opposed views—and a call for rethinking the Anthropocene on the basis of the evidence of concrete
Concrete can indeed be taken as a stratigraphic marker of the Anthropocene, as the defense suggests. But the prosecution’s case for the time-transgressive character of concrete is also compelling. The jury is invited to consider that the diachroneity of the signal cannot be overlooked. It is almost as though the stratigraphic evidence of concrete challenges the concept of the Anthropocene to reformulate itself to fit what is actually in the ground. The amount of concrete in strata certainly does increase in the post–Second World War period, but this is perhaps more of an acceleration of existing trends rather than a sudden manifestation of a new material. The existence of a substantial layer of bomb rubble corresponding to the start of the Anthropocene found across large parts of London is disputed. As in other European cities, much war rubble was removed and taken to outlying areas, where it was used to fill in stream valleys and other hollows, or to create hills like the Teufelsberg in Berlin. In places, large amounts of concrete can be found in strata deposited in earlier periods, notably in strata dated to the late nineteenth and early twentieth centuries and the Roman period (27 BCE–476 CE).
On the basis of such evidence, if concrete is to be used as a stratigraphic marker of the Anthropocene, the Anthropocene thus marked should be regarded as an emergent or unfolding time unit such as a biozone or event,18 which does not carry the necessity to specify a precise starting date.
Cristián Simonetti is Associate Professor in Anthropology at the Pontificia Universidad Católica de Chile.
Matt Edgeworth is Honorary Visiting Fellow in the School of Archaeology and Ancient History at the University of Leicester, UK.
Please cite as: Simonetti, C, M Edgeworth (2022) Concrete: A Stratigraphic Marker for the Anthropocene. 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/tewg-cp32
