“When did the Anthropocene begin? A mid-twentieth century boundary level is stratigraphically optimal”

Zalasiewicz, J., et al., 2015. Quaternary International, 383, pp. 196-203.
We evaluate the boundary of the Anthropocene geological time interval as an epoch, since it is useful to have a consistent temporal definition for this increasingly used unit, whether the presently informal term is eventually formalized or not. Of the three main levels suggested – an ‘early Anthropocene’ level some thousands of years ago; the beginning of the Industrial Revolution at ∼1800 CE (Common Era); and the ‘Great Acceleration’ of the mid-twentieth century – current evidence suggests that the last of these has the most pronounced and globally synchronous signal. A boundary at this time need not have a Global Boundary Stratotype Section and Point (GSSP or ‘golden spike’) but can be defined by a Global Standard Stratigraphic Age (GSSA), i.e. a point in time of the human calendar. We propose an appropriate boundary level here to be the time of the world’s first nuclear bomb explosion, on July 16th 1945 at Alamogordo, New Mexico; additional bombs were detonated at the average rate of one every 9.6 days until 1988 with attendant worldwide fallout easily identifiable in the chemostratigraphic record. Hence, Anthropocene deposits would be those that may include the globally distributed primary artificial radionuclide signal, while also being recognized using a wide range of other stratigraphic criteria. This suggestion for the Holocene–Anthropocene boundary may ultimately be superseded, as the Anthropocene is only in its early phases, but it should remain practical and effective for use by at least the current generation of scientists.


With Anthropocene Working Group (AWG) Chair Zalasiewicz as lead author and 24 other members of the group listed as co-authors, “When did the Anthropocene begin?” has been received as a trial balloon for the AWG’s final recommendation to the International Commission on Stratigraphy (ICS). (This impression is perhaps confirmed by a more elaborate and recent version of the argument by Waters et al. that is acknowledged to be an official contribution of the AWG, but which I don’t consider here.) Varied responses to the article are indicative of how the popularity of the Anthropocene idea and public turmoil regarding anthropogenic climate change are intruding into the official deliberations among geologists about the Geological Time Scale (GTS). Additional unusual pressure stems from tension between separate academic disciplines brought together for the topic of the Anthropocene and seeing in it reason to challenge established research protocols, including those in other fields. Geologists are not being left to their own devices. Hamilton, for example, insists that the development of Earth System science at more or less the same time that anthropogenic global warming became a subject of research and a matter of public concern constituted a Kuhnian paradigm shift in Earth sciences. Noting the interdisciplinary composition of the AWG, he claims that adjudicating the position of the Anthropocene in the GTS should involve participants from multiple Earth sciences and an attention not only to the geological record but to fundamental changes in the functioning of the Earth System. In contrast, Finney and Edwards’s refutation of “When did the Anthropocene begin?” polices strictly the propriety of the ICS, noting that changes to the Earth System do not necessarily correspond to divisions of the GTS.

In spite of this surfeit of context, the objective of the article is quite narrow. On the basis of the already considerable literature on the topic of the Anthropocene, the authors propose to identify an initial stratigraphic time boundary that is practically “singular, globally synchronous, and commonly understood” (2). They assert that such a proposal need not address whether the Anthropocene should be formalized in the GTS. Continued use of the term as “an unofficial stratigraphic time” also warrants a coherent, unambiguous designation. And they insist that naming a lower boundary does not imply that further inquiry into the Anthropocene cannot take place on the Holocene side of the divide (and vice versa, if the Anthropocene is considered an epoch rather than an age within the Holocene). They evaluate three potential durations: an early Anthropocene associated primarily with the spread of agriculture thousands of years ago, an industrial Anthropocene dated to approximately the beginning of the nineteenth century, and the mid-twentieth century period that earlier writings on the Anthropocene called the Great Acceleration.

Citing Ellis among others, they acknowledge that thousands of years ago humans already influenced the Earth System, but they are ultimately not persuaded by such an early date because the “significance of the Anthropocene lies not so much in seeing within it the ‘first traces of our species’ (i.e. an anthropocentric perspective upon geology), but in the scale, significance and longevity of change (that happens to be human-driven) to the Earth system” (4). The industrial Anthropocene is more convincing because it achieves a “more considerable perturbation than that achieved in pre-industrial times.” They find, however, that setting the initial boundary of the Anthropocene in eighteenth century industrialization would not be stratigraphically effective because, as in the earlier period, the evidence is diachronous and distributed unevenly. The most recent of the three prospects affords the authors a number of stratigraphically significant signs such as the global dispersal of “artificial radionuclides” from nuclear explosions, lead waste (from gasoline) in polar ice, the carbon isotope signal associated with ~120 ppm increase in CO2, shore to shore oil-spill residue from rapid increases in (accident-prone) marine oil-tanker traffic, a “spate of urbanization” that will be recorded in the land, “technofossils” such as mobile phones that extend the evidence past mid-century, and so on (4-5).

Because the nuclear explosions starting in 1945 dispersed “artificial radionuclides worldwide,” they propose the following singular, globally synchronous, and commonly understood boundary. The Anthropocene can be said to begin “historically at the moment of the detonation of the Trinity A-bomb at Alamogordo, New Mexico at 5:29:21 Mountain War Time … July 16, 1945 … This would have a parallel with the Cretaceous-Paleogene boundary which, although defined by “Global Boundary Stratotype Section and Point” (GSSP–called a “golden spike”) at El Kef, Tunisia, has been expressly placed at the moment of impact of the meteorite on the Yucatan Peninsula” (5). The difference between the location in Tunisia and the instant of the asteroid strike refers to a technical distinction between a golden spike placed to mark “rock units” (Finney and Edwards 5) and a “Global Standard Stratigraphic Age” (GSSA) marker that is represented in years relative to the present. Zalasiewicz et al. claim that in the case of the Anthropocene a GSSP does not provide a “practical advantage over a GSSA” (5).

To capture the appeal and utility of a precise moment in time, the authors cite a sign of anthropogenic causes for climate change that is resulting in the sixth great extinction and compare it to the Chicxulub Asteroid, which was the direct cause for the extinction of the dinosaurs. This association of the Trinity test with an asteroid striking Earth illustrates a challenge of identifying human activity as a dominant geological force. It is difficult to establish a hard and fast distinction between, to borrow from Ellis, sociocultural niche construction in the Holocene and, with apologies to Ellis, sociocultural niche destruction in the Anthropocene.

Ellis is a co-author of “When did the Anthropocene begin?” Readers of his ESA Centennial Essay will discern his influence in the article’s description of pre-industrial anthropogenic influences on the Earth System. But the argument for a mid-twentieth century Anthropocene ultimately runs counter to his theoretical demonstration of the ways that today’s unprecedented “scale, significance and longevity of change to the Earth system” (Zalasiewicz et al. 6) can be linked to evidence of human sociocultural niche construction throughout much of the Holocene and even earlier.

In “Defining the epoch we live in,” Ruddiman, Ellis, Kaplan, and Fuller respond directly to the choice of July 16, 1945:

Selecting 1945 as the start of the “Anthropocene” would implicitly omit … extensive agricultural and early-industrial alterations. Does it really make sense to define the start of a human-dominated era millennia after most forests in arable regions had been cut for agriculture, most rice paddies had been irrigated, and CO2 and CH4 concentrations had been rising because of agricultural and industrial emissions? And does it make sense to choose a time almost a century after most of Earth’s prairie and steppe grasslands had been plowed and planted? Together, forest cutting and grassland conversion are by far the two largest spatial transformations of Earth’s surface in human history. From this viewpoint, the “stratigraphically optimal” choice of 1945 as the start of the Anthropocene does not qualify as “environmentally optimal.” (39)

I have cited them at length to display their rhetorical questions along with this last reference to “environmentally optimal,” which I imagine may be an instance of interdisciplinary push back against the geological priority of a synchronic marker to describe phenomena that are more accurately identified diachronically. Convinced that the term Anthropocene will persist in spite of disagreements over its province, they recommend it be used informally with a small “a,” which would allow for appropriate modifiers such as “early agricultural” or “industrial” (39). Such utility would guard against presentist misrepresentations of the long historical record of anthropogenic environmental change that they summarize in counterpoint to “When did the Anthropocene begin?”

“Defining the epoch we live in” makes its case against the recent Anthropocene – or for an atomic anthropocene – with a succinct but detailed historical account of massive change to the Earth’s surface effected by human activity over thousands of years. Not addressed directly is the contention that the measure of the Anthropocene is the “considerable perturbation” of the Earth system. “Perturbation” is an alarming word choice more in concert with representations of the Anthropocene as a catastrophic rupture that has divorced Earth from – for us and many other species – the more hospitable climes of the Holocene. Ellis adopts an opposite stance. A signatory to An Ecomoodernist Manifesto’s pronouncements about the possibility of a “good, even great Anthropocene,” Ellis insists we should not regard it as a crisis (2011). Its difference from the Holocene is in degree and not kind. I take his optimism to have a theoretical basis in “Ecology in an anthropogenic biosphere.”

A key claim of the Ellis essay we are examining in this series of posts is that human ultrasociality has long been characterized by practices and organizations of shared intentionality that mean human niche construction is sociocultural. This finding informs Ellis’s contention that defining human ecological sustainability according to natural limits or the “carrying-capacity” of the Earth (a la Malthus or The Population Bomb) is mistaken. Encouraged as I am to be directed away from romantic conceptions of nature as essentially wilderness without us, I am also disturbed to ask if Ellis’s theory of sociocultural niche construction allows not just for maladaptive developments – he is emphatic that it does just as he reiterates his recognition of the devastating effects of anthropogenic climate change – but for the possibility of maladaptations that would irreversibly transform the conditions in which we endeavor to exercise shared intentionality? In other words, can Ellis’s account of early anthropocene “cultures of nature” be reconciled with accounts of the Anthropocene that define it on this side of a rupture from the Holocene?

References & Further Reading
Breakthrough Institute (2015) An Ecomodernist Manifesto. San Francisco: Breakthrough Institute.
Ellis, Erle. (2011) “The Planet of No Return: Human resilience on an artificial earth.” Love Your Monsters: Postenvironmentalism and the Anthropocene. Breakthrough Institute. eBook.
Finney, Stanley C. and Lucy E. Edwards. (2016) “The ‘Anthropocene’ epoch: Scientific Decision or political statement?” GSA Today 26 (3-4): 4-10. DOI: 10.1130/GSATG270A.1
Hamilton, Clive. (2016) “The Anthropocene as Rupture.” The Anthropocene Review February 22, 2016, DOI: 10.1177/2053019616634741
—. (2015) “Getting the Anthropocene so wrong.” The Anthropocene Review 2(2):102-107. DOI: 10.1177/2053019615584974
Ruddiman, William F., et al., (2015) “Defining the epoch we live in.” Science, 348: 38-39. DOI: 10.1126/science.aaa7297
Waters, Colin N. et al., (2016) “The Anthropocene is functionally and stratigraphically distinct from the Holocene.” Science, 351: 137-147. DOI: 10.1126/science.aad2622

5 thoughts on ““When did the Anthropocene begin? A mid-twentieth century boundary level is stratigraphically optimal”

  1. Welcome to the blog, Jim, and thanks for your really thoughtful dig into the details of the complicated and fraught question of when the Anthropocene began. You point to some closely related issues I think are really interesting.

    First, I think you identify a really interesting tension that I think arises from the interdisciplinary character of the Anthropocene idea. On the one hand it’s a commonplace that understanding and responding to the phenomena associated with the Anthropocene requires unprecedented collaboration across natural and social science—and of course as you have helped our campus understand via discussions of Chakrabarty, the humanities must respond to the science. But on the other hand, the research community that has the conceptual resources to articulate the Anthropocene concept with real rigor is in Geology, in particular in the ICS. But their methods seem to push for a start date on the basis of methodological criteria (e.g. a uniform, synchronous signal)—which perhaps subordinates important factors that get highlighted in other disciplines.

    In particular, and this leads to another issue, the geological criteria don’t have much to do with providing an explanation of the signal. So the comparison between the Chicxulub Asteroid and the Trinity Test, while rhetorically powerful (your domain, given your disciplinary background I guess) doesn’t shed much light on what made the Trinity Test possible—it is “exogenous” to the system, like a big rock from outer space. But of course the A-bomb didn’t come out of nowhere—and the accounts of social learning and cultural transmission and development of knowledge that Ellis’ draws on seem to provide some important ingredients for an explanation.

    And this is what I think is ultimately at stake in the start date controversy: the ability to provide a comprehensive explanation of the phenomena of the Anthropocene. Ellis doesn’t aim to do that in the paper we’re reading—he is focused on the Biosphere, not the Earth System as a whole (hence the push-back he receives from Hamilton). But in advocating for an earlier start date (or maybe even for punting on the issue altogether), I think he and the other “early Anthropocene” researchers are helping historicize the Anthropocene, in the sense of providing some tools that don’t just describe it, but also work toward giving it a more detailed causal explanation.

  2. Zev and I had an offline exchange about the geologic time scale — Zev asked 
“Why is preserving the integrity of the Geologic Time Scale (GTS) so important: what is it that the GTS does? How is it used in Geology (and elsewhere) that makes those methods/criteria so valuable?”

    Keeping in mind that I do not serve on the Stratigraphic Commission, so am an outsider to the formal process, I nevertheless am a trained geologist, and we are trained to take the Geologic Time Scale very seriously. Our training begins with our introductory undergraduate geology course, where the concepts of time, age, and methods of dating occupy a primary role. Time is central to our existence, but we perhaps find it difficult to define, especially when contemplating “deep” time — geological time. Harvard paleobiologist Stephen Jay Gould called the concept of deep time “the greatest contribution of geology to human thought.” The GTS was developed before the invention of any means to measure time quantitatively. The latter was enabled (ultimately) by the discovery of radioactivity in the early 20th century, and this led to the first accurate date of the age of the earth — roughly 4.5 billion years— in 1953. Prior to this, the geological time scale existed, and the various divisions of the time scale were ordered in a relative sense— the Cambrian is older than the Ordovician, and Permian strata are older than Triassic strata, for instance. The boundaries between these divisions were/are recognized on the basis of major events, because time is marked by events— it is the duration between events. So those who “police” the time scale do so by defining boundaries on the basis of events that will show up in the geologic record, and be recognizable (ideally) globally. These are the arguments underpinning the choice of the 1945 date for the start of the Anthropocene — because nuclear fallout has been preserved in the rock (sediment) record globally beginning at this time, and is readily detectable. An important goal of the timescale is to be able to mark boundaries that are synchronous globally— for the same reason that, if time is important to you, you synchronize your watch to the accurate time, rather than a time that might be an hour, or half hour, or 5 hours different from the accurate time. Now, traditionally, this meant that boundaries on the geologic time scale have been marked by major extinction events. The Permian-Triassic (= Paleozoic-Mesozoic) boundary and the Cretaceous-Paleogene (=Mesozoic-Cenozoic boundary) are prime examples— two of the “Big Five” extinctions known in the history of life. Smaller subdivisions are placed at smaller extinction events. Indeed, it is exactly because geology represents history that time occupies such a central role. Geologists reconstruct histories of past Earths, and we do so by correlating events globally, because by doing so we explore “alternative Earth systems” — states with which we are not familiar, but that are within the bounds of behavior of the Earth system. Accurate dating is what enabled geologists to infer that an event— or perfect storm of events— killed the dinosaurs (and a lot of other life). If, as some have suggested, we are entering Earth’s sixth mass extinction, then this will be a global “event” readily detectable to those studying the future geologic record, albeit this will occur over some finite interval of time. So that is one distinction— geologists do not customarily speak of time with precisions measured in single years or decades, but rather we are happy with error margins measured in centuries and– for deep time– more. In the case of the start of the Anthropocene, some argue it can be pinned to a particular day.

    • Thanks so much for the clarification, Lynn!

      Just to push this a bit further, though, let me ask: say that the Working Group relents and goes with an “Early Anthropocene” start date, even in the face of the standard criteria (i.e. global scale and synchronicity). What would be lost by doing this? Would it it make it harder to “do” Geology in the way it has been done if the Anthropocene were a different kind of period than the rest?

      I ask this to try to get at what is finally at stake for the people who argue for 1945, or who oppose designating the Anthropocene as an official period at all, specifically on the grounds of maintaining the integrity of the classification system.

      Is it, finally, that the earlier starting point doesn’t pick out something that is “event-like” enough? That’s how I understand your comment–am I right? If so, then I’m led back to the question that underlay my comment–namely, maybe what we see here are the difference in projects between Geology and other disciplines which are interested in the Anthropocene. This may be too reductive, but maybe from a purely Geological perspective the longer-term processes at work in the “early Anthropocene” are just not relevant to what Geology cares about–as interesting as they are to what other disciplines care about.

      It this is true, what does this say about the interdisciplinary interaction among different fields that are concerned about the Anthropocene? Off the top of my head I’d say it suggests that the goal ought not to be a merging of disciplines into some more general super-discipline (though I don’t know if anyone (except Hegel) thinks that’s a good, or even feasible, idea). Rather, I think it supports the notion that disciplines need to maintain some degree of integrity, and that interdisciplinarity involves an openness to how other disciplines go about their business. This allows for work that is informed by the range of disciplinary approaches, if not some monumental synthetic discipline that replaces all others (again, maybe not anything anyone really believes in anyway).

  3. Well, first I should clarify that, whereas the subdivisions for most of the GTS (especially the last 540 My during which animals with hard parts existed) rely on first/last appearances of lifeforms (i.e., extinction/radiation events), the criteria for the finer subdivisions of the Quaternary period are linked in part to climate events. As I understand it, part of the reason lies in the different durations of pre-Quaternary epochs/ages versus Quaternary ones— the latter represent much shorter time intervals (e.g. the Holocene of ~12,000 yrs). The Anthropocene, if formalized as a unit, could be MUCH shorter.

    Getting back to your question— or questions— what would be lost by going with an earlier date? Keeping in mind the disclaimer that I am a mere bystander to this discussion, my sense is that it relates (for many geologists) to the criteria typically used and accepted for boundary definitions of the timescale. In other words, it is viewed by some as potentially setting a precedent for GTS boundary definitions. Pertinent to this is a recent article (Finney and Edwards, 2016) in the newsletter of the Geological Society of America that questions whether the drive to formalize the “Anthropocene” is a scientific or political statement. Finley and Edwards (2016) argue “The stratigraphic record of the Anthropocene is minimal, especially with its recently proposed beginning in 1945; it is that of a human lifespan, and that definition relegates considerable anthropogenic change to a “pre-Anthropocene.”

    Finney, S.C., and Edwards, L.E., 2016, The “Anthropocene” epoch: Scientific decision or political statement?: GSA Today, v. 26, p. 4-10. doi: 10.1130/GSATG270A.1

  4. Update, almost a year on . . . here’s a statement from Zalasiewicz et al. (in Nature this week) that both gives a clear sense of the criteria geologists apparently have in mind for a starting point for the geological Anthropocene (as they call it). They are responding directly to the critique offered by Ellis that the Anthropocene be understood in terms of broad human impact, not just the impact inscribed in the strata.

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