This transcript has been edited for clarity.

JZ: Hello, my name is Jan Zalasiewicz and I am an Emeritus Professor of Palaeobiology at the University of Leicester and I was Chair of the Anthropocene Working Group from 2009–2020.

RD: And my name is Rowan Deer, and I am part of the editorial team for the website anthropocene-curriculum.org, where we have been producing online guides to the Anthropocene Working Group’s research. Thank you, Jan for agreeing to speak with us. 

JZ: You’re very welcome. 

RD: So the Anthropocene is a proposed geological epoch in which the Earth has been significantly altered by human impacts. Officially ratifying the Anthropocene as a unit of the geological time scale involves defining a starting point, which—within the current research—is set to be in the mid-twentieth century. The clearest and most globally-synchronous markers for this are the traces of mid-century nuclear bomb testing. But there are arguments that a long running geological “event” would better capture the full range and duration of human impacts on the planet, including things like megafaunal extinctions, widespread deforestation, and the use of fire. So, Jan, why does the Anthropocene Working Group think that an epoch, with a defined starting date in the 1950s, better captures the planetary transformations that we are calling the Anthropocene?

JZ: The sum total impact of humans of course goes back many thousands of years—perhaps 50,000 years into the Pleistocene. But right from the very beginning, from Paul Crutzen’s improvisation of the term or concept, the Anthropocene was never meant to capture the full range, extent, and history of human impacts. It was not a human change, it was a planetary change. So the idea of an Anthropocene epoch captures the transformative impacts of humans upon the planet, something which is much more recent and something which is much more globally synchronous. The Anthropocene isn’t an event, but, geologically, it includes many distinct events. For instance, there’s a carbon isotope event, a plastics dissemination event, a radionuclide dissemination event, and so on. Geologically, each of these give specific event markers to the strata and many of them cluster around the mid-twentieth century, around what’s been called the Great Acceleration. Those can help define the Anthropocene rather than being in opposition to it. This is simply the way that geology works, not just for the Anthropocene, but generally. Events of different kinds are used to define geological time units, way back into the geological past. So, for instance, an asteroid impact event defines the end of the Cretaceous, the beginning of the Paleogene, a carbon isotope event defines the beginning of the Eocene, and so forth. The Anthropocene is no different, so it can accommodate events as a basis for an epoch, a proposed chronostratigraphic unit.

RD: And so this distinction between event and epoch, which is obviously very clear to you and other geologists, perhaps is not so clear to the broader public and doesn’t really feed into the way that the term Anthropocene is actually already being used in lots of non-geological contexts—in the media, in newspapers. Can you elaborate a little bit more on how this kind of informal usage differs from the proposed official ratification and why that difference matters? 

JZ: The Anthropocene is used in different ways. As with many concepts, in geology and beyond geology, a concept comes in and then is used in different ways—it balloons out to take on a variety of other meanings. As a palaeontologist, I’m familiar with that with regards to palaeontological species, which are described as one thing and then, through successive descriptions, take on other shapes, other morphologies, as part of the definition. So, yes, because some of these distinctions are not widely appreciated, because they involve stratigraphic technicalities, there has been confusion about what the Anthropocene is and isn’t. Having said that, my feeling is that there is a central truth to the way that the Anthropocene is often—maybe not always, but often—used in wider discourse, in the media and so on, as something that is transforming the planet from the kind of stability and familiarity of the Earth and its system into something that is evolving to be quite different. And that is essentially what Paul Crutzen was getting at. We hope the work of the Anthropocene Working Group on proposing a definition of the Anthropocene will help clarify and stabilize the meaning of the term Anthropocene.

RD: So do you think this kind of wider usage has affected the concerns and processes of the Anthropocene Working Group in any way? Or is that just something that’s going on outside of your work and not really affecting it?

JZ: We’re very aware of it, because we deal with a range of queries, a range of inquiries, we answer different critiques of the Anthropocene. So this is part of our background and our work. I think it’s helped us sharpen our own image of the Anthropocene—on what it is and what it isn’t—in working towards a technical definition. So in that sense, it’s been useful, not least because the Anthropocene is such a new concept. So it has had to be built up more or less from scratch, at least in terms of a geological reality. This kind of discussion has been very good practice in defining what the Anthropocene should and shouldn’t include. It’s not always been easy, but on the whole it’s helped the process along.

RD: Something else that is new about this research is that the Anthropocene Working Group is the first working group of the Subcommission on Quaternary Stratigraphy to include humanists and social scientists. Can you say a little bit about how they have contributed to the work of the group and whether there have been any particular challenges or successes within this interdisciplinary endeavor?

JZ: We are not just the first Quaternary group, I think we are the first of any group through the whole of geological time to include non-stratigraphers, non-geologists, on a technical panel to define a geological time unit. So we’re very much taking a leap into the unknown there. It makes sense, because with the Anthropocene we’re dealing with an overlap of human time—human historical time; observed, recorded time—and geological time, geologically-recorded time, within strata as chemical signals, as fossils, as things like that. So given this fusion or combination of different kinds of evidence, it seemed sensible to take on board archaeologists, historians, even an international lawyer, to look at the wider implications of the kind of work that was being done by the Anthropocene Working Group. Clearly it was a steep learning curve for all of us, because we had to become accustomed to our different perspectives, our different range of skills and experience, our different philosophies, our different approaches to time. Some of the approaches to time in geology are quite distinctive and not used by other disciplines. But on the whole it’s been tremendously rewarding. I think the business of establishing these transdisciplinary kinds of understanding have given the Anthropocene Working Group energy and a sense of inspiration, which has been quite unique—at least within geology—and has enormously helped the work of the group. It’s been a great adventure, I have to say. 

RD: That’s wonderful to hear. Since 2013, the Anthropocene Working Group has also been collaborating with Haus der Kulturen der Welt, an arts and cultural institution in Berlin, Germany. Can you tell us a little bit more about this collaboration—how it came about and how it has developed? 

JZ: Well, it would be very much a personal perspective and you at the Haus der Kulturen der Welt will know the history far better than I do. To me, it’s been quite extraordinary. And I think it’s been terrifically rewarding, certainly for the sciences and hopefully for the humanities side as well. I remember very vividly the first meeting. It was a new kind of world to me. I think I was the only geologist amongst several hundred artists, humanists, social scientists, and others. So it was quite a privilege to be there. And I have two reactions to this terrific adventure that you all started. The first is regarding the scale and the persistence of the work that has been carried out. I think you had the first major exhibition on the Anthropocene—one that really tried to take it seriously—but it was more than that. It wasn’t just catching something that was just at the front of the Zeitgeist and then moving on. There was continual involvement after that, with the Technosphere, the Anthropocene Curriculum, and all of those other related projects. And of course it’s still going strong almost a decade later. This to me is extraordinary. And second, while that has been taking place, there’s been an evolution to incorporate more of the sciences: the physical sciences, geology in particular, but other ones too. And of course that has culminated in making possible funding, in enabling the work on the Anthropocene GSSP candidates. And so HKW is now at the technical heart of the work on the Anthropocene. Again, to me, it’s marvelous, it’s quite remarkable, I don’t know of anything else quite like it and I still don’t quite believe it’s happening, but I’m happy that it is.

RD: Let’s dig a little bit more into the practicalities of the GSSP research that the Anthropocene Working Group have been doing. Have there been any particular methodological changes? What’s different about ratifying the Anthropocene compared to any other geological epochs?

JZ: In general, this work, which is examining a range of candidate sites for a GSSP, is being done fairly classically—in fact, very classically—and within the tradition of work that was done on the Jurassic, Cretaceous, Carboniferous, and so on. It’s the systematic examination of signals in sequences of strata to try to establish patterns and trace them globally to see which would make the best time reference for a geological time unit. The Anthropocene research is going by the book. There are some novelties, of course, there are some novel kinds of signal. There are things like plastics, radionuclides, and fly ash, which are things that one doesn’t get in older strata, but they form patterns through time just as other signals do. So it’s a novelty in a technical sense, but philosophically it’s the same kind of thing. And this kind of incorporation of new signals is taking on a trend that’s been evolving within geology generally over the past several decades. GSSPs always used to be defined on fossils, but then a couple of decades ago the Eocene became defined on the basis of a geochemical signal. They always used to be defined in marine strata, but then, even more recently, the Holocene became defined within a polar ice cap. And so the kind of innovation of the Anthropocene is simply following that kind of trend. 

There is one change, one difference, I think, which is substantive. And that is the sheer number of candidate sites. There are twelve, whereas with most geological time units there’ve usually been two, three, four—sometimes only one candidate has been put forward. And I think that reflects the novelty of the Anthropocene, because at the same time as defining it, we also have to understand it and characterize it globally in terms of its geological signals. And that means examining a wide range of environments—the peat bogs, the lakes, ice cores, coral skeletons—to see which will provide the best, most widely traceable, and sharpest signal. So that is genuine research being done as a consequence of having to build up this subject, this discipline of Anthropocene stratigraphy, in a short time from almost nothing. When we started, we didn’t have an idea quite what it would be, what it would involve, and how we would go about things. Now we have a much better idea, but we still have to cast our net wide.

With the other geological time units there had already been up to a couple of centuries of systematic work on them: the concept had been established, defined, used by generations of geologists. There was a good understanding of what it was, what signals were there, which were the best sections, which were the best ones to use. There was a tradition to follow, so by the time it came to establishing the GSSP, people had a pretty good idea of where exactly to look for them. And sometimes there were competing ideas, of course, but not to that scale of looking across the whole range, because that work had already been done. With the Anthropocene, it’s been much more a kind of frontier science because of its novelty in many ways. This means that the GSSP work will give a much broader and more wide-ranging area of understanding—both of the Anthropocene as a whole and how to trace across different timelines within it.

RD: What might be the implications of this research? What might be the scientific, cultural, or political implications of the Anthropocene being officially ratified as a geological time unit?

JZ: Well it’s important to note first that ratification still hangs in the balance. It has always been in the balance because the Anthropocene is so new, so different, so brief. It comes with so much baggage that other geological time units don’t come with. Quite how it will be received by the wider stratigraphic community who decides on these things is still in the balance and there are still discussions to be had. Ratification, if that happens, will help establish the unit and stabilize it for use within both scientific work and wider discussions. And of course it will underline the scale and speed of the Earth system changes upon which the Anthropocene concept is based. And knowing that ratification is not a given, I think the central concern of the Anthropocene Working Group throughout its work has been to try and establish the evidence for the Anthropocene as a geological time unit as thoroughly, clearly, scrupulously, and systematically as possible and to communicate that evidence as best we can—both for specialist communities of geologists and more widely. The thing that will remain, whatever the ratification decision, will be this demonstration of a new kind of planetary reality—which Paul Crutzen first crystallized as the Anthropocene concept. The preservation of that reality and that narrative will  hopefully be of lasting value and the main legacy of the Anthropocene Working Group.