# The proposed Anthropocene Epoch/Series is underpinned by an extensive array of mid-20th century stratigraphic event signals

Martin J. Head, Jan A. Zalasiewicz, Colin N. Waters, Simon D. Turner, Mark

Williams, Anthony D. Barnosky, Will Steffen, Michael Wagreich, Peter K.

Haff, Jaia Syvitski, et al.

► To cite this version:

Martin J. Head, Jan A. Zalasiewicz, Colin N. Waters, Simon D. Turner, Mark Williams, et al. The proposed Anthropocene Epoch/Series is underpinned by an extensive array of mid-20th century stratigraphic event signals. Journal of Quaternary Science, 2022, 10.1002/jqs.3467. hal-04720499

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Article:

# The proposed Anthropocene Epoch/Series is underpinned by an extensive array of mid-20th century stratigraphic event signals

MARTIN J. HEAD¹*, JAN A. ZALASIEWICZ², COLIN N. WATERS², SIMON D.

TURNER³, MARK WILLIAMS², ANTHONY D. BARNOSKY⁴, WILL STEFFEN⁵,

MICHAEL WAGREICH⁶, PETER K. HAFF⁷, JAIA SYVITSKI⁸, REINHOLD

LEINFELDER⁹, FRANCINE M.G. MCCARTHY¹, NEIL L. ROSE³, SCOTT L. WING¹⁰,

ZHISHENG AN¹¹, ALEJANDRO CEARRETA¹², ANDREW B. CUNDY¹³, IAN J.

FAIRCHILD¹⁴, YONGMING HAN¹¹, JULIANA A. IVAR DO SUL¹⁵, CATHERINE

JEANDEL¹⁶, J.R. MCNEILL¹⁷, and COLIN P. SUMMERHAYES¹⁸.

1. Department of Earth Sciences, Brock University, St. Catharines, Ontario, Canada

2. School of Geography, Geology and the Environment, University of Leicester, Leicester, UK

3. Environmental Change Research Centre, Department of Geography, University College London, London, UK

4. Jasper Ridge Biological Preserve and Department of Biology, Stanford University, Stanford, CA, USA
5. Fenner School of Environment and Society, Australian National University, Canberra, ACT, Australia

6. Department of Geology, University of Vienna, Vienna, Austria

7. Nicholas School of the Environment, Duke University, Durham, NC, USA

8. INSTAAR, University of Colorado, Boulder, CO, USA

9. Department of Geological Sciences, Freie Universität Berlin, Berlin, Germany

10. Department of Paleobiology, Smithsonian Museum of Natural History, Washington, DC, USA

11. State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China

12. Departamento de Geología, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU, Bilbao, Spain

13. Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, UK

14. School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK

15. Leibniz Institute for Baltic Sea Research Warnemüende (IOW), Rostock, Germany

16. LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, Toulouse, France

17. Georgetown University, Washington DC, USA

18. Scott Polar Research Institute, University of Cambridge, Cambridge, UK

E-mail: mjhead@brocku.ca

<footnote>*Correspondence: Martin J. Head, as above.</footnote>
ABSTRACT: The extensive array of mid-20th century stratigraphic event signals associated with the 'Great Acceleration' enables precise and unambiguous recognition of the Anthropocene as an epoch/series within the Geological Time Scale. A mid-20th century inception is consistent with Earth System science analysis in which the Anthropocene term and concept arose, and would reflect the reality that our planet has sharply exited the range of natural variability characterizing the Holocene Epoch/Series, which the Anthropocene would therefore terminate. An alternative, recently proposed 'geological event' approach to the Anthropocene is primarily an interdisciplinary concept, encompassing historical and socio-cultural processes and their global environmental impacts over a diachronous timeframe that extends back at least many millennia. Resembling more closely a geological *episode* than an *event*, it would decouple the Anthropocene from its chronostratigraphic delineation and association with an abrupt planetary perturbation; but separately defined and differently named it might be usefully complementary. We recommend a clear separation of *epochs*, *events*, and *episodes*. An *epoch* is a formal subdivision of the geological time scale, and its correlation may be assisted by one or more *events*; an *event* is usually, and particularly in the Quaternary, a brief incident or perturbation with a sedimentary expression; whereas an *episode* is a longer, internally complex time interval that may include several *events* and even extend across several *epochs*.

KEYWORDS: Earth System science; Quaternary; epoch; episode; event; chronostratigraphy

**Introduction**

Gibbard et al. (2022) in the Journal of Quaternary Science (JQS) recently proposed that the Anthropocene be considered a prolonged, diachronous ‘geological event’ encompassing all *transformative* impacts of humans upon Earth, rather than a formally
defined chronostratigraphic unit. The proposal restated arguments published by the same authors in the journal *Episodes* (Gibbard *et al.*, 2021), a repetition justified on the grounds that ‘*Episodes* might not be widely read by Quaternary scientists’. We have submitted a response to the earlier article (Head *et al.*, *in press*) and have prepared a wider analysis of the event concept for publication elsewhere (Waters *et al.*, *submitted*). Here, in like manner, we briefly reiterate for the *JQS* readership our response to their arguments.

The late Paul Crutzen, working within the Earth System science community, conceptualized the Anthropocene as a geological time interval during which human impacts propelled our planet far beyond the natural variability of the Holocene Epoch. Crutzen suggested that its beginning might be placed at the late 18th century onset of the Industrial Revolution in Europe (Crutzen and Stoermer, 2000; Crutzen, 2002) but noted (pers. comm. to M. Meybeck, 2003) that a proposed mid-20th century beginning (Meybeck, 2001) might work equally well. Since 2009, the Anthropocene Working Group (AWG) of the Subcommission on Quaternary Stratigraphy (SQS) has been formally testing this concept chronostratigraphically. They recognised the key geological significance of a major mid-20th century upturn in the rate and magnitude of numerous global socio-economic indicators and Earth System trends that had been identified by the Earth System science community, and termed the Great Acceleration (Steffen *et al.*, 2004, 2007, 2015; Head *et al.*, 2021a). Many of the Great Acceleration drivers have already produced clear signatures in geological records of the mid-20th century on a global scale.

The plentiful and growing evidence that Great Acceleration geological signals support the formal definition of an Anthropocene epoch/series has been extensively documented (Waters *et al.*, 2016; Zalasiewicz *et al.*, 2017, 2019, 2020; Syvitski *et al.*, 2020; Head *et al.*, 2021a). On the basis of this evidence, a non-binding vote of the AWG in 2016 supported a chronostratigraphically defined Anthropocene at the rank of series/epoch (Zalasiewicz *et al.*,
2017). A supermajority binding vote in 2019 reaffirmed that the Anthropocene should become a formal chronostratigraphic/geochronologic unit within the international Geological Time Scale (GTS), its base aligned with stratigraphic signals dating to the mid-20th century (AWG, 2019; Fig. 1). This process now continues with the analysis of 12 reference sections from which one will be proposed as the Global boundary Stratotype Section and Point (GSSP) (Waters et al., 2018; Head et al., 2021a). Such chronostratigraphic characterization of the Anthropocene would align with the working Earth System science definition of the term (Steffen et al., 2016). The Anthropocene as such effectively represents a *planetary response* to human driving forces. Its accompanying geological signals are essentially simultaneous and worldwide, and would be just as significant if caused by an agency other than humans. The stratigraphic signals cluster closely around the mid-20th century, are supported by observational and instrumental records, and allow practical chronostratigraphic precision to within a decade or less.

Despite the wealth of data favouring a chronostratigraphic Anthropocene, Gibbard et al. (2021, 2022) proposed an alternative interpretation: that the Anthropocene be considered a geological ‘event’ and not a formally defined unit of the GTS. They conceptualized this ‘Anthropocene event’ as a highly time-transgressive and flexibly interpreted unit incorporating *transformative* human cultural practices, extending as far back as the Late Pleistocene megafaunal extinctions, and yet facilitating ‘*robust stratigraphic characterization*’ (Gibbard et al., 2021, p. 1). Their proposal prompts a novel appraisal of the Anthropocene concept, and anthropogenic impacts generally, through the lens of geological event stratigraphy, and has stimulated discussion of how events are recognised and used in stratigraphy (Waters et al., submitted). Here we focus on: the characterization of the Anthropocene by Gibbard et al. (2021, 2022); the question of whether a chronostratigraphic Anthropocene should be at age/stage or series/epoch level; the *event* interpretation by
Gibbard et al. (2021, 2022) vis-à-vis the usual meaning of events in geology and particularly within the Quaternary; whether an ‘Anthropocene event’ may be geologically robust; and how this suggested conceptualization might relate to an Anthropocene epoch.

**The Anthropocene as a geological epoch**

Gibbard et al. (2021, 2022) stated that because significant anthropogenic influence on the stratigraphic record extends over millennia (perhaps over fifty millennia; their fig. 1), such influence should be reflected in the definition of the Anthropocene. This contrasts starkly with the Anthropocene as conceived ‘for the current geological epoch’ by Paul Crutzen (Crutzen and Stoermer, 2000, p. 17; contra Gibbard et al., 2022, p. 3), its use by the Earth System science community, and its subsequent analysis by the AWG. A clear distinction is here made between the protracted, diachronous early record of anthropogenic impacts through the Late Pleistocene and Holocene, which had a relatively small impact on Earth System function, and the much more recent, profound, and abrupt planetary changes to landscape, biosphere and climate that underpin the Anthropocene of chronostratigraphy and Earth System science.

These striking and often irreversible planetary changes, most clearly associated with the ‘Great Acceleration’, are obscured in figure 1 of Gibbard et al. (both 2021 and 2022) and in their text. Our Figure 2 quantifies specific trends in order to show the true magnitudes and rates of change. A large body of observational evidence (Syvitski et al., 2020, 2022) shows that human actions from the mid-20th century onwards have driven the Earth System beyond the Holocene envelope of variability and into a new planetary state, the full extent of which will be determined by a combination of ongoing human pressures and planetary feedbacks (Steffen et al., 2018). Human- and especially technology-driven changes are already profound as regards their rates (IPBES, 2019; IPCC, 2021) and magnitudes (Waters et al.,
2016; Head et al., 2021a), producing major impacts on five great Earth spheres – the biosphere, atmosphere, hydrosphere, cryosphere, and the surface of the lithosphere. Direct human perturbation of the biosphere combined with global warming are driving rapid changes in ecosystem function and biological communities (Williams et al., 2016, in press), with increasing rates of species extinctions since the beginning of the 20th century (Ceballos et al., 2015), severe declines in vertebrate populations from the 20th century onwards (Ceballos et al., 2017, 2020; WWF, 2020), unprecedented and irreversible homogenization of once distinct biographic assemblages (Williams et al., in press), a dramatic increase in a wide range of anthropogenically-derived contaminants, and rapidly increasing global atmospheric surface temperature since 1970 (Sippel et al., 2021). The late 20th and early 21st centuries also saw changes in atmospheric circulation and precipitation patterns; warming of the upper ocean, rising sea level and coastal erosion; acidification of the oceans and the spread of oxygen-deficient ‘dead zones’; increasingly severe extreme weather events such as heatwaves (terrestrial and marine), tropical cyclones, wildfires, and intense rainfall and flooding; a trajectory towards increasing megadroughts; and wholesale retreat of the cryosphere.

Earth System science analysis clearly indicates a marked change in planetary state from the mid-20th century, and increasing perturbation of oceanic and atmospheric circulation is driving changes in global geochemical, nutrient, sediment and hydrological cycles. The Earth's climate trajectory has very likely escaped from its pacing by Milankovitch (orbital) cycles with consequences that will persist for at least many millennia (Ganopolski et al., 2016), while changes to biodiversity and biogeographic assemblages will be even more long-lasting (Williams et al., 2015, 2016). The primary drivers of these fundamental changes to the Earth System stem from human impacts, and mostly from their steep post-mid-20th
century increase (Sytvitski *et al.*, 2020, 2022). These observations are all consistent with the Anthropocene as a new epoch in Earth history (Steffen *et al.*, 2016).

Mirroring these observed changes is an extensive array of geological signals in strata from the mid-20th century onwards that provides a stratigraphically robust basis for recognizing the base of the Anthropocene – and hence to support a chronostratigraphic boundary, not replace it (see below). This evidence is abundant, confined to a short time interval, often novel in composition, and global in distribution (Waters *et al.*, 2016; Zalasiewicz *et al.*, 2019; Syvitski *et al.*, 2020; Head *et al.*, 2021a).

The suggestion by Gibbard *et al.* (2022) that a formal chronostratigraphically defined Anthropocene would be impractical because it fails to include all significant human impacts is incorrect given that all GSSPs, when viewed at the finest scale, cut indiscriminately through Earth history, as already illustrated for the Meghalayan Stage GSSP (Head *et al.*, 2022). Even so, on practical grounds the base of a formal Anthropocene defined by a close array of mid-20th century stratigraphic signals would be far easier to recognise than a diachronous lower boundary characterised by diffuse anthropogenic signals each requiring interpretation as to its significance in planetary transformation. However, we agree that an *episode* shaped by interdisciplinary characteristics and encompassing these earlier human impacts (Gibbard *et al.*, 2021) could, if appropriately named, be complementary to a formally defined Anthropocene epoch. For instance, archaeological periods, including the Mesolithic, Neolithic, and Bronze Age, are useful because their time-transgressive boundaries accommodate the varying onsets of particular technological developments around the world, as Gibbard *et al.* (2022) note. But this diachroneity is revealed only when a time scale is added. The onset of the Neolithic dates to the latest Pleistocene in the Near East (Ibáñez *et al.*, 2018), the Early Holocene in North Africa (Mulazzani *et al.*, 2017), and the Middle
Holocene in northern Europe (Nordqvist and Mökkönen, 2017) – these two schemes, one archaeological and the other chronostratigraphic, clearly complement one another.

Any formal chronostratigraphic boundary requires a primary stratigraphic guide that will enable correlation from its GSSP on a global scale. The AWG decided by supermajority vote in 2019 upon the tight array of mid-20th century stratigraphic signals as the primary guide to the proposed Anthropocene epoch (AWG, 2019). Presently favoured (Zalasiewicz et al., 2017) is the radiogenic signal generated from fallout produced by above-ground thermonuclear weapons testing, which shows a marked upturn in sedimentary records globally in the early 1950s (Waters et al., 2015, 2019). Functionally, this would be analogous to the impact fallout used as the primary guide to the Cretaceous–Paleogene boundary (Molina et al., 2006), as both signals are near-isochronous and global in extent. However, Gibbard et al. (2022) question whether such a guide would be welcomed by the international geological community given its association with weapons of mass destruction. Here it must be emphasized that the AWG has adopted a scientific approach, not a sociopolitical one, where stratigraphic utility determines the selection of the primary guide. We note that few, if any, of the signals associated with potential definition of a chronostratigraphic Anthropocene have positive connotations.

## The Anthropocene as potential stage of the Holocene

The speed and scale of those more recent changes noted above, a large number of which are geologically long-lasting, already irreversible, and rising sharply from the mid-20th century onwards, demonstrate beyond reasonable doubt that conditions characterizing the Holocene Epoch have already ended. To match this, a substantial and highly distinctive stratigraphic record has already accumulated as a material consequence. These changes are far greater than those associated with the temporary climate oscillations used for the tripartite subdivision of
the Holocene (Walker *et al.*, 2018, 2019), and overall rival or exceed in scale those associated
with the Pleistocene–Holocene transition (Waters *et al.*, 2016; Syvitski *et al.*, 2020; Head *et
al.*, 2021a). There is therefore an overwhelming case for an Anthropocene epoch and series to
succeed the Holocene. Indeed, *not* to recognise the Anthropocene formally in this way would
result in the GTS, which inherently reflects major phases of Earth’s evolution, in this case
departing from observed geological reality. In accordance with required practice, the
proposed GSSP for an Anthropocene series/epoch would also define the base of its associated
stage/age, which will take the name of the GSSP locality (Salvador, 1994). It would not be
subdivided into subseries/subepochs owing to its brief duration to date (Fig. 1).

Event stratigraphy and the Anthropocene

An *event* in geology is informal, and hence cannot comprise one of the hierarchical
ranks of units within the International Chronostratigraphic Chart, the basis of the GTS. It
refers to a distinct *happening* in time (Salvador, 1994, p. 73), but does not have a counterpart
in chronostratigraphic terminology and so has come to refer to both the event itself and its
geological expression. *Event stratigraphy* typically refers to the stratigraphic traces of events,
whether depositional, erosional or geochemical (Rawson *et al.*, 2002). These are not
significantly diachronous, and Ager (1973), who introduced the term, specifically valued
events for their ability to trace time planes across diachronous boundaries (fig. 7.1 in Ager,
1973; fig. 1 in Head *et al.*, 2022). For Ager (1973), and also Salvador (1994, p. 117), the
most stratigraphically useful geological events are brief, and essentially instantaneous such as
meteorite impacts, tsunami floods, storms that generate tempestites, and volcanic ashfalls,
(e.g., Walliser, 1996).

It therefore misleads to suggest (Gibbard *et al.*, 2021, 2022) that geological events are
time-transgressive by nature, for they have been used as a crucial tool for the event-based
recognition of chronostratigraphic boundaries (Salvador, 1994, p. 79). Examples include the
8.2 and 4.2 ka climatic events that serve as primary stratigraphic guides in formally
subdividing the Holocene (Walker *et al.*, 2018, 2019). It is the Quaternary application of the
event concept that is most relevant to the Anthropocene. An event stratigraphy approach is
used to identify and correlate stadial-interstadial oscillations in Greenland ice cores for the
Late Pleistocene and Early Holocene (Rasmussen *et al.*, 2014). Even those events of
relatively long duration, such as Greenland Stadial 1 (GS-1 which is broadly equivalent to
the Younger Dryas stadial or 'event'), have abrupt onsets and/or terminations that constitute
precise, isochronous reference points for the event stratigraphy (Rasmussen *et al.*, 2014, p.
15). In these and other examples (see discussion in Head *et al.*, 2022), the conceptualization
of geological events for the Quaternary in general is therefore markedly different from the
concept employed by Gibbard *et al.* (2021, 2022).

However, the term *event* has over time also been liberally applied to longer-duration
and variably diachronous phenomena. The specific examples quoted by Gibbard *et al.* (2021)
– the Great Oxidation Event (GOE), the Great Ordovician Biodiversification Event (GOBE),
and the Middle–Late Devonian forestation of continents – lasted for tens of millions of years
and lie at the extreme end of this spectrum (and indeed, the last of these has to our knowledge
not previously been designated as an ‘event’). For these phenomena, the term ‘episode’
(NASC, 2005) not ‘event’ (Salvador, 1994) is appropriate. The GOE and GOBE are
protracted, internally complex and variously diachronous stratigraphic intervals whose status
as events has been contested, the former being explicitly categorized as an episode (Shields *et
al.*, 2022, Poulton *et al.*, 2021; see also Servais and Harper, 2018 and Servais *et al.*, 2021
regarding the GOBE).

Each such episode typically includes numerous more conventionally understood
events – some of which may define or support chronostratigraphic boundaries, as in isotopic
events associated with oxygenation now being considered for use in developing a GSSP-
based pre-Cryogenian chronostratigraphy (Shields et al., 2022). More widely, event
stratigraphy is now being increasingly used in defining chronostratigraphic boundaries, as
with the carbon isotope anomaly used as the primary marker for the Paleocene–Eocene
boundary (Aubry et al., 2007), the palaeomagnetic reversal events that are the primary
markers for the Neogene–Quaternary (Head, 2019) and Early–Middle Pleistocene boundaries
(Suganuma et al., 2021), and most famously the bolide event that defines the Cretaceous–
Paleogene boundary (Molina et al., 2006).

Similarly, the anthropogenic ‘event’ of Gibbard et al. (2021, 2022) is much better
conceptualized as a protracted, diachronous *episode* that incorporates the effects of human
predation on megafauna, development of agricultural cultivation and deforestation, transfer
of species through introduction of colonial trade, and the impacts of the Industrial
Revolution. These can be clearly separated from the stratigraphically significant global array
of events at or around the mid-20th century level that may be used to support a Holocene–
Anthropocene chronostratigraphic boundary (Fig. 1). They include the appearance of novel
components such as radionuclides in fallout from atmospheric nuclear testing, pesticides and
plastics, marked upturns in concentrations of CO2, CH4, heavy metals including Pb, fly ash
particulates, black carbon, non-sea-salt-sulfur, accelerated species extinctions and rapid inter-
biogeographical translocations of non-native species, and the effects of temperature and sea-
level rises, shifts in δ13C and δ15N and reduced fluvial sediment flux (e.g., Waters et al.,
2016; Syvitski et al., 2020; Head et al., 2021a; Williams et al., in press). Geological events
are thus not an alternative to chronostratigraphy, but rather they offer crucial
contextualization and commonly assist in definition.

This more tightly constrained interval – in reality characterized by a unique cluster of
distinct lithological, chemical and biological event markers (Fig. 2) that enable extremely
high-resolution correlation – is consistent with event stratigraphy as originally proposed by Ager (1973) and with how the event concept is widely used in the Quaternary. Its value here lies in its practical application to chronostratigraphy. The earlier impacts of humans are certainly critical to understanding how the Earth System came to be changed, and in tracing the history of human impacts in leading to these changes. But they are neither globally synchronous nor as clearly marked, tightly clustered, and as varied as the geological signals occurring in the mid-20th century.

Many stratigraphically significant mid-20th century signals comprising the Great Acceleration event array are not mentioned by Gibbard et al. (2021, 2022). These include the influx into sedimentary successions worldwide of plastics and many other novel entities, fly ash and black carbon (soot), persistent organic pollutants and artificial radionuclides; global carbon and nitrogen isotope anomalies as a result of hydrocarbon burning and nitrogen production respectively; and a wide range of correlatable bio-events mostly linked to the introduction of non-native species. They have been exhaustively detailed (e.g., Waters et al., 2016; Zalasiewicz et al., 2019; Head et al., 2021a; Syvitski et al., 2020, 2022; Williams et al., in press) and can act to characterize and define a synchronous, globally traceable Holocene–Anthropocene boundary, in exactly the same way that a carbon isotope event defines the Paleocene–Eocene boundary, and a bolide event defines the Cretaceous–Paleogene boundary.

## Conclusions

Some geological phenomena that have been termed ‘events’ are actually time-transgressive, multi-temporal and spatially variable (Gibbard et al., 2021, 2022), but others more consistent with the conventional understanding of the term are near-isochronous and may have global extent. Events are used extensively for chronostratigraphic applications in
the Quaternary, most notably the 8.2 and 4.2 ka climatic events used to subdivide the Holocene Epoch into its respective formal subepochs (Fig. 1). The chronostratigraphic Anthropocene as an epoch/series with a base coincident with a rich array of stratigraphic event signals dating to the mid-20th century is the evidence-based definition used by the AWG, and offers a robust chronostratigraphic datum of global extent that is not provided by the interdisciplinary anthropogenic ‘event’ concept proposed by Gibbard et al. (2021, 2022). Furthermore, in focusing on the Great Acceleration, a planetary perturbation caused by human activities rather than the activities themselves, it aligns with the definition used by the Earth System science community from which the term Anthropocene originated. This community routinely uses the stratigraphic record to identify past changes in the state of the Earth System. The Anthropocene as an epoch would be identified through comparable rigorous processes of definition as, and named in agreement with, other epochs in the Cenozoic Era. The ‘Anthropocene event’ of Gibbard et al. (2021) by contrast, is neither a stratigraphic nor chronostratigraphic concept, but rather encompasses an interdisciplinary and broadly defined range of phenomena with variable physical expression unified only by being anthropogenic (Head et al., in press). It operates at mostly local to regional scales on land, with little application to the oceanic realm. Embracing wide variation in interpretation and scope, its application may depend on distinguishing transformative human-induced changes from other such changes, and indeed from those caused by non-human drivers. Resembling more closely an episode than an event, this is a very different concept to the chronostratigraphic Anthropocene, but separately defined and differently named might usefully complement it.
We are most grateful to C. Neil Roberts and the editorial team at JQS for their review and swift handling of our manuscript. MJH acknowledges support from a Natural Sciences and Engineering Research Council of Canada Discovery Grant.

*Author contributions*—The article was drafted by M.J.H and J.A.Z., and improved by C.N.W., S.D.T., M.Wi, A.D.B., W.S., and M.Wa., after which all authors contributed to the final published version. All authors approved the final publication.

*Abbreviations*.

AWG, Anthropocene Working Group; b2k, before the year 2000 CE; GA, Great Acceleration; GOBE, Great Ordovician Biodiversity Event; GOE, Great Oxidation Event; GSSP, Global boundary Stratotype Section and Point; GTS, International Geological Time Scale; ICS, International Commission on Stratigraphy; IGBP, International Geosphere-Biosphere Programme; IUGS, International Union of Geological Sciences; *JQS, Journal of Quaternary Science*; PAGES, Past Global Changes; SQS, Subcommission on Quaternary Stratigraphy.

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Figure 1. Geological time scale for the Quaternary, as sanctioned by the International Union of Geological Sciences / International Commission on Stratigraphy (from Head et al., 2021b), but with the Anthropocene added as a proposed new series/epoch, as conceived by the AWG. Ratified boundaries are identified by a golden spike symbol (indicating a Global boundary Stratotype Section and Point; GSSP) whereas pending and proposed boundaries are marked by a grey spike symbol. The primary guide used for global correlation to each GSSP is given, where GA event array = Great Acceleration event array. Each of these primary guides is chronostratigraphic in nature and could be considered an ‘event’, and two are explicitly so labelled. The informal and diachronous ‘anthropogenic episode’ here shown schematically, corresponds with the informal, diachronous and interdisciplinary ‘Anthropocene event’ of Gibbard et al. (2021, 2022).

Figure 2. Geological and historical timelines using empirical data to show the true scale and timing of social and environmental changes shown in figure 1 of Gibbard *et al.* (2021). a) fossil fuel consumption (https://ourworldindata.org/fossil-fuels); b) CO₂ emissions from fossil fuels (https://ourworldindata.org/co2-emissions#global-co2-emissions-from-fossil-fuels-global-co2-emissions-from-fossil-fuels); c) CO₂ and CH₄ data from Antarctic ice cores and direct atmospheric measurements (https://ourworldindata.org/atmospheric-concentrations and https://www.epa.gov/climate-indicators/climate-change-indicators-atmospheric-concentrations-greenhouse-gases respectively); d), e) and f) anthropogenic biomes (https://ourworldindata.org that uses data from Ellis *et al.*, 2020 from 10,000 BCE to 2015 CE); g) extinction rates (Pimm *et al.*, 2014), where E/MSY is the number of extinctions per million species years; h) first record rate (per year) of all neobiotic species reported by Seebens *et al.* (2017), although data after 2000 CE (grey dots) are incomplete owing to the delay between sampling and publication; i) global trade data is from
https://ourworldindata.org on exports as % GDP 1500 CE to present; and j) global charcoal influx (biomass combustion): data from (left panel) Power *et al.* (2008) and (right panel) Marlon *et al.* (2008).
IUGS/ICS time scale with Anthropocene added

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