<<

Downloaded from http://sp.lyellcollection.org/ by guest on October 26, 2013

Geological Society, , Special Publications Online First

The '' in the context of formal geological classification

P. L. Gibbard and M. J. C. Walker

Geological Society, London, Special Publications, first published October 25, 2013; doi 10.1144/SP395.1

Email alerting click here to receive free e-mail alerts when service new articles cite this article Permission click here to seek permission to re-use all or request part of this article Subscribe click here to subscribe to Geological Society, London, Special Publications or the Lyell Collection How to cite click here for further information about Online First and how to cite articles

Notes

© The Geological Society of London 2013 The term ‘Anthropocene’ in the context of formal geological classification

P. L. GIBBARD1* & M. J. C. WALKER2 1Department of Geography, Cambridge , University of Cambridge, Cambridge CB2 3EN, UK 2School of , and Anthropology, Trinity Saint David, University of , Lampeter SA48 7ED, UK *Corresponding author (e-mail: [email protected])

Abstract: In recent , ‘Anthropocene’ has been proposed as an informal stratigraphic term to denote the current interval of anthropogenic global environmental change. A case has also been made to formalize it as a /, based on the recognition of a suitable marker , such as the start of the Industrial Revolution in northern Europe. For the Anthropocene to merit formal definition, a global signature distinct from that of the is required that is marked by novel biotic, sedimentary and geochemical change. Although there is clear evidence of anthropogenic effects in geological sequences, it is uncertain whether these trends are suffi- ciently distinct, consistent and dated for the proposal for a Holocene/Anthropocene boundary to be substantiated. The current view of the Earth-Science community is that it should remain infor- mal. For formal definition a Global Stratigraphic Section and Point (GSSP) is required. Adoption of the term ‘Anthropocene’ will ultimately depend on recognition of a global event horizon. Without this, there is no justification for decoupling the Anthropocene from the Holocene. If the Anthropo- cene is deemed to have utility, it should be as an informal historical designation rather than a for- mally defined stratigraphic unit (of whatever status) within the geological timescale.

The ‘Anthropocene’ (meaning anthro¯pos ‘human palaeoenvironmental reconstructions. These anthro- being’ and kainos ‘new’) is a term that has pogenic effects, which have reached significant become increasingly widely used since it was first levels during the last few , and particularly proposed by Paul Crutzen & Eugene Stoermer since the Industrial Revolution in northern Europe, (2000) to denote the interval, in have resulted in marked changes to the Earth’s which many geologically significant processes and surface. Indeed, almost every aspect of the contem- conditions have been, and continue to be, pro- porary global environment is now modified, or at foundly altered by human activities. Processes least influenced, by human activity (Crossland include changes in erosion and sediment transport 2005; Zalasiewicz et al. 2010; Steffen et al. 2011). resulting from agriculture and urbanization, and There is a body of opinion within the geological variations in the chemical composition of the atmos- community that this accelerated human impact phere, oceans and soils, with notable perturbations may be reflected in the recent stratigraphic record, in element cycling, such as carbon, nitrogen, phos- and that the anthropogenic effect can be dis- phorus and various metals. Changes in environmen- tinguished from natural ‘background’ conditions tal conditions generated by these various processes (Zalasiewicz et al. 2008). Although the term include global warming, ocean acidification and Anthropocene was initially invoked informally to coastal eutrophication and ensuing anoxia; habitat describe this period of expanding human influence loss, species range shifts and extinctions; and glob- on the global environment (Crutzen 2002), and ally significant physical and chemical changes, was apparently suggested by chance (Steffen et al. including cryospheric loss, ozone depletion and 2004), it is increasingly being applied to the recent accelerating eustatic sea-level rise (e.g. Orr et al. geological record, where the term is viewed, by 2005; Nicholls et al. 2007; Chen et al. 2011; Urban some, as being equivalent to those used as series- et al. 2012). status subdivisions of the (‘recent The increasing prominence of humans dur- life’), notably the and Holocene. ing the present (Holocene Series/Epoch) intergla- An important consequence of the recognition of cial has been marked by a progressive increase the increasing intensity of human impact on the in their effect on the natural environment and its natural environment, and its possible manifestation processes, and this has long been recognized in in the geological record, has been the initiation of

From:Waters, C. N., Zalasiewicz, J. A., Williams, M., Ellis,M.A.&Snelling, A. M. (eds) A Stratigraphical Basis for the Anthropocene. Geological Society, London, Special Publications, 395, http://dx.doi.org/10.1144/SP395.1 # The Geological Society of London 2013. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics P. L. GIBBARD & M. J. C. WALKER discussions to determine whether the stratigraphic to form a parallel, numerical timescale based on signature of the Anthropocene is now sufficiently years. Chronostratigraphical divisions are ‘time/ clearly defined to warrant its formal definition as a rock’ units, that is they refer to the sequence of new period of geological time (Zalasiewicz et al. rocks deposited during a particular interval of 2011a, b). This is currently being considered by time. Geochronological divisions are the corre- a Working Group of the Subcommission on Qua- sponding intervals of (continuous) geological time. ternary (SQS). In the meantime, a sep- Thus, it can be said that rocks of the Quaternary arate Working Group of the SQS, jointly with were deposited during a time interval INTIMATE (integration of ice-core, marine and called the Quaternary Period. terrestrial records), has been examining the case In conventional stratigraphic practice, it is for a formal subdivision of the Holocene Series/ generally accepted that chronstratigraphical and Epoch (M. J. C. Walker et al. 2012). In the light geochronological boundaries should, as far as of a possible conflict between the two groups, possible, be defined in continuous sedimentary the Holocene working group has not considered sequences. Ideally, such sequences preserve mul- the Anthropocene question. Nevertheless, they tiple lines of evidence (multi-proxy records) and, acknowledge that although there is a clear distinc- in particular, continuous sedimentation spanning tion between these two initiatives, the Holocene the boundary itself, that is, excluding time gaps. subdivision being based on natural climatic/ This continuity offers the opportunity for identify- environmental events and the concept of the ing, inter alia, palaeontological, isotopic, chemical Anthropocene focusing on the human impact on and palaeomagnetic changes, and therefore enables the envi-ronment, there may indeed be areas of the boundary to be identified as precisely as possible overlap. We return to the subdivision of the Holo- within the limits of the evidence contained within cene below. the sequence. Throughout the , this In this paper we consider the designation of the approach provides not only a basis for accurately Anthropocene as a formal time-stratigraphic unit delimiting a boundary, but also a means by which against the background of these ongoing discus- that horizon can be extended beyond the stratotype sions. We examine the term Anthropocene in the locality for purposes of correlation. context of the formal definition of geological time- The recommendations of the International Stra- scale units, particularly in relation to the require- tigraphic Guide (Hedberg 1976; Salvador 1994) ment for relating such units to unequivocal Global require that all major chronostratigraphical subdivi- Stratotype Section and Point (GSSP, ‘golden sions are defined with reference to boundary strato- spike’) localities, and we also evaluate the potential type localities in sediment reference sequences. value and utility of defining the episode of recent These are designated GSSPs, or ‘golden spikes’, human activity as a new stratigraphic unit within and form the basis for the division of geological the geological timescale (GTS). time in the internationally sanctioned GTS. This is the responsibility of the International Commis- sion on Stratigraphy (ICS), which is a constituent Stratigraphic procedures and the group of the International Union of Geological geological timescale Sciences (IUGS), the body that directs all aspects of global geoscience. The role of the ICS is to The stratigraphy of geological sequences is the formulate the subdivision, classification and deter- foundation upon which the discipline of historical mination of geological time, that is, chronostrati- , and therefore the accurate reconstruction graphy and . The ICS operates of Earth history, depends. It is concerned with all through subcommissions, each associated with a the elements of sedimentary successions, including particular time period, the Subcommission for their form, distribution, lithology, fossil content, Quaternary Stratigraphy (SQS), for example, being depositional environment, vertical sequence and responsible for the Quaternary (which includes the . Stratigraphy is therefore a synthetic subject present ). Each of the subcommissions defines that examines the origin, and temporal and spatial the time divisions for their respective periods, and distribution, of sediment strata and other rocks. the GSSPs that provide the basis for global corre- (‘time-rock stratigraphy’) is lation. Proposals are submitted to the IUGS, via the branch of stratigraphy that involves the appli- the ICS, for formal ratification. Any changes that cation of time to rock successions, the goal of arise from the proposal are incorporated into the which is the establishment of a globally applicable GTS (www.stratigraphy.org). Once a GSSP has standard timescale. The chronostratigraphical scale been ratified by the IUGS, a 10- moratorium originated as a relative one that was calibrated pri- on any change then applies. An alternative basis marily through the application of biostratigraphy. for defining a global stratotype is age and is referred Reliable numerical ages have been added gradually to as a Global Standard Stratigraphic Age (GSSA). FORMALIZING THE ‘ANTHROPOCENE’

This is a chronological reference point in the late (Lourens et al. 2005). ‘Astronomical world’s rock record that is used to define a bound- pacing’ provides both an index of the major climatic ary, and has been employed most widely in the shifts and a basis for estimating the age of these where the lack of diagnostic fossils events. As a consequence, major intervals of geo- precludes the identification of recognizable GSSPs. logical time within the and the Quater- As with a GSSP, boundaries defined in this way nary, which are evident in the climatic record, can must also be ratified by the ICS to be internationally be further defined as chronostratigraphic units valid (Remane et al. 1996). within the GTS (Zalasiewicz et al. 2004). The GTS is based on a hierarchical system of classification in which time-rock sequences (chron- Subdividing the Quaternary record ostratigraphy) and their corresponding intervals of time (geochronology) are represented by units of Although stratigraphical procedures are of para- progressively lower rank. The Quaternary has the mount importance to working in all the rank of system (a chronostratigraphical periods, from the Pre- to the Ceno- high rank) and period (the equivalent geochronolo- zoic, applications of conventional stratigraphic gical unit) within the Cenozoic Erathem/ (Sal- practice are frequently far from straightforward vador 2006a, b). The Pleistocene is traditionally in the Quaternary. This is because Quaternary geol- placed within the Quaternary at the next-lower ogists are attempting to subdivide what might rank of series (chronostratigraphy) or epoch (geo- appear to be very short periods of time across a ). The lower boundary of the Quaternary range of different environments from the tops of Series/Pleistocene Epoch is located at the GSSP at mountains to the depths of the oceans. The extra- the base of the /Age in the Monte ordinarily limited time intervals that are recognized San Nicola section, Sicily, and dated at 2.58 Ma. in the Quaternary require a critical understanding Both the lower boundary of the Quaternary, and of the implications of stratigraphical analysis and its status as a unit of series/stage rank, were ratified procedures, and the essential distinctions between by the IUGS in 2010 (Gibbard et al. 2010). the various subdivisions of rock strata that allow for the effective division, correlation and recon- struction of history from rock sequences. In this The position of the Holocene sense, the fundamental need to identify and define reference sequences (GSSPs) that can be used to As currently defined, Holocene (meaning ‘wholly equate isochronous surfaces and events around the modern’) is the name for the most recent inter- world becomes critical. This is a requirement not val of Earth history and includes the present day. only for large-scale units, such as Stages or Series, It is the series or epoch of the Quaternary but also for smaller-scales subdivisions. System/Period, and the boundary stratotype (GSSP) The conventional approach to the subdivision of is located in the Greenland NGRIP and the Quaternary stratigraphic record is to employ evi- dated to 11.7 ka (Walker et al. 2009). dence for contrasting climatic conditions to char- The origin of the term Holocene is inextricably acterize individual stratigraphic units (geologic– linked to the development of the nomenclature climatic units). This follows recommendations by of ice-age time divisions. Two terms arose inde- the American Commission on Stratigraphic Nomen- pendently in the early to mid-nineteenth clature (1961, 1970), which recognized a geologic– to encompass near-surface, often unconsolidated, climatic unit as indicating ‘an inferred widespread deposits: the Quaternary (Desnoyers 1829; Reboul climatic episode defined from a subdivision of 1833; von Morlot 1854) and the Pleistocene (Lyell Quaternary rocks’ (ACSN 1970, p. 31). Although 1839), although the former considerably predates climatostratigraphy does not always find favour this usage, having been proposed by Giovanni with geologists working in older parts of the Arduino in 1759 for the fourth stage or ‘order’, record, in the Quaternary, where climatic change which he recognized as the alluvial sediments of is the hallmark of the two million years, it is the Po plain, in northern Italy (Schneer 1969; Rodo- difficult to envisage a scheme of stratigraphic sub- lico 1970). Both Quaternary and Pleistocene were division that does not specifically acknowledge originally established for marine deposits, in the this fact (Lowe & Walker 1997). Indeed, it is now Paris basin and in eastern England, respectively. apparent that the principal driver of recent global However, with the recognition that the extensive climatic fluctuations, namely variations in Earth’s ‘Drift’ or ‘Diluvial’ deposits represented greatly orbit and axis (Milankovitch forcing), is reflected extended glaciation in recent Earth history, both not only in key stratigraphic horizons within the soon became synonymous with the Ice Age, and Quaternary record, but can also be detected in pre- latterly with the rise of humans. The Quaternary Quaternary sequences at least as far back as the differed in encompassing Lyell’s (1837) ‘Recent’ P. L. GIBBARD & M. J. C. WALKER or Forbes’ (1846) ‘Postglacial’, a period termed the and Holocene; that is, the term would have Series Holocene by Gervais (1867–69), with the latter for- or Epoch status. If this was accepted, the corol- mally adopted by the 1885 International Geological lary is that the Holocene has ended and we have Congress (IGC). entered a new geological interval, and such a tran- The terms ‘Recent’, or less formally ‘Postgla- sition would be equivalent to the changes between cial’, as alternatives to the Holocene, although still the and the , or the and commonly used by geologists, are invalid (cf. the . In our view, a change of this magni- Gibbard & van Kolfschoten 2005). A further term, tude is not supported by the geological evidence, the ‘Flandrian’, derived from marine transgression sedi- Anthropocene episode being too limited in duration ments on the Flanders coast of Belgium (Heinzelin when viewed from the perspective of the present, & Tavernier 1957), has often been used as a and with too variable a global stratigraphic signa- synonym for Holocene (e.g. Nilsson 1983, p. 23). ture to justify its elevation to a time-stratigraphic It has been adopted by authors who consider that unit of Series or Epoch rank within the internation- the last 10 ka should have the same stage status as ally agreed geological timescale. previous interglacial events and thus be included The current position is that we are living in the in the Pleistocene. In this case, the latter would Holocene Series/Epoch, and one of the key jus- thus extend to the present day (cf. West 1968, tifications for defining a Holocene Series, as a sep- 1977, 1979; Woldstedt 1969; Hyva¨rinen 1978). arate entity from the Pleistocene, is that humans However, this usage has been continually criticized (Homo sapiens) reached critical numbers and began (e.g. Morrison 1969) and has been losing ground influencing natural systems from the beginning of over the last three (Flint 1971, p. 324; this time period onwards. As noted above, without Lowe & Walker 1997, p. 16). Accordingly, the this unique record of human impact there would term Holocene Series/Epoch is now more widely be no justification for the Holocene being anyth- adopted, partly in recognition of the modern usage ing other than an interglacial, in common with all but also, more importantly, because of the impor- others in the Pleistocene. If the human dimension tance in the present interglacial of the evolution of is accepted as a reasonable basis for a separate the human environment. Indeed, it is this anthro- Holocene Series, as distinct from the Pleistocene, the pogenic signature that is the hallmark of the Holo- activities of humans cannot then be used again in cene, setting it apart from previous interglacials, support of a discrete Anthropocene division. Given and taken as a fundamental justification for its the extensive archaeological record of human/ status as a time-stratigraphic unit of Series/Epoch environment interaction throughout the Holocene rank as it is currently defined (Walker et al. 2009). (and even in earlier ), many workers find it difficult to accept the fact that ‘the Holocene inter- glacial has ended’. Indeed, when seen in the What status for the Anthropocene? context of the long-term climatic and environmen- tal changes that have occurred during the Quatern- As noted above, the status of the Anthropocene is ary, there would seem to be little justification for currently being examined by a Working Group of this view. the SQS. Both within that group and outside, there We referred above to the Working Group that is an increasing body of opinion in support of the is considering a subdivision of the Holocene. The view that the informal nature of the term ‘Anthro- proposals of that Working Group are for a tri- pocene’ should be replaced by a formal definition partite subdivision of the Holocene Series/Epoch (e.g. Williams et al. 2011). If so, the Anthropocene (Early, Middle and Late Holocene Sub-Series/Sub- would become the most recent time-stratigraphic Epochs), with boundaries at 8.2 and 4.2 ka respect- subdivision of the GTS, and would constitute a for- ively. The GSSP for the Early–Middle Holocene mal unit of the Quaternary System/Period. Whether boundary is found in a stable isotope record from such a formalization is justified (and, if so, at what the archived Greenland NGRIP ice core, and the rank within the geochronological/chronostratigra- GSSP for the Middle–Late Holocene boundary is phical hierarchy) is now considered. also in a stable isotope record, this time from an The status of a potential formal Anthropocene archived stalagmite from Mawlmuh Cave, NE division is one of considerable philosophical impor- India (M. J. C. Walker et al. 2012). These boundaries tance. This is because the higher the term’s rank, are based on significant natural events that register the greater the difference between conditions pre- globally: the 8.2 ka event was an abrupt cooling served and represented within the stratigraphic episode triggered by catastrophic meltwater release unit, and those of the immediately previous division. into the North Atlantic from ice-dammed lakes at In the case of the term ‘Anthropocene’, the name the northern margins of the Laurentide ice sheet, selected implies, either intentionally or otherwise, the signal of which can be found in both hemi- that it should be seen as equivalent to Pleistocene spheres, while at c. 4.2 ka there was a worldwide FORMALIZING THE ‘ANTHROPOCENE’ aridification episode that was most pronounced in America, have expanded, flourished and collapsed low- and mid-latitude regions, but which is also (Diamond 2005). Each has left an imprint in the recorded in various proxy records from high-latitude archaeological and geological record, and any of regions. The point here is that these events are these could have been designated a marker for reflected in stratigraphic records from different increased human influence, yet the limited spatial parts of the world as broadly time-parallel marker impact of these cultures makes it unlikely that horizons, so the GSSPs are of global significance. their stratigraphic signal could be used to define As such, the proposal for a subdivision of the Holo- the onset of a period of global human dominance. cene is fully in line with the stratigraphic principles The rapid industrialization of Western Europe and and practices described above. If a Holocene/ eastern North America during the eighteenth and Anthropocene boundary is to have the same credi- nineteenth centuries was, by contrast, an event of bility, then it must be underpinned by anthropo- much wider significance, but both industrialization genic events that are as globally significant as the and urban development was spatially variable and natural events that form the basis for the proposed diachronous. It has therefore been suggested that Holocene GSSPs. In other words, the definition of an independent marker horizon, such as the increase the base of the Anthropocene must conform to the in CO2 in polar ice cores (Crutzen 2002), could be same stratigraphic principles. used to designate the boundary between the Holo- Three questions follow from these discussions. cene and Anthropocene. A rise in CO2 levels from (1) Is there a globally significant, human-induced around AD 1750 is evident in both Arctic and and broadly time-parallel event that could form Antarctic records (Barnola et al. 1995; Etheridge a basis for a stratigraphic boundary between the et al. 1996), is accompanied by the beginnings of Holocene and Anthropocene? (2) Are we now liv- an upward trend in the curve for CH4 and N2O ing in a geological period that is significantly dif- (MacFarling Meure et al. 2006; Sowers 2010), ferent from the preceding Holocene? (In other and reflects increased levels of atmospheric trace- words, can the Holocene be considered to have gas loading. As Zalasiewicz et al. (2011b) have ended?) (3) Would the recognition of the Anthro- pointed out, however, although seemingly abrupt pocene as a new geological period be of value to on centennial timescales, these changes tend to be the wider Earth Science community? too gradual to provide useful stratigraphic mark- In relation to the first of these questions, it has ers at an annual or even decadal level, and this been suggested that the onset of the Anthropocene chronological imprecision is further exacerbated could be defined by the rapid industrialization and by the delay in sealing of the air bubbles during urbanization of western Europe and eastern North snow accumulation on the ice-sheet surface, which America in the late eighteenth century (Crutzen & results in a temporal offset between the annual Stoermer 2000), and numerous references have ice-core timescale and the atmospheric CO2 record been made to the fact that evidence of these anthro- (Bender et al. 1997). Stratigraphic resolution to pogenic activities is preserved within the recent the annual level, which is the aim of a GSSP for geological record (Steffen et al. 2007; Zalasiewicz the Anthropocene (Zalasiewicz et al. 2011b), is et al. 2008; Williams et al. 2011). For example, therefore unlikely to be obtained from the ice-core the development of urban societies over the past record. two centuries has created ‘urban strata’ (e.g. the An additional difficulty with using the history of ‘artificial strata’ of Rosenbaum et al. 2003), while trace gases in ice cores to define the onset of the expanded town and city sites have influenced a Anthropocene is that, although this is perhaps the range of geomorphological (e.g. fluvial) and pedolo- clearest and most unequivocal indicator of human gical processes, and will have left their mark in stra- impact on the global atmospheric environment in tigraphic sequences. Indeed, it has been suggested the recent geological past, unfortunately it has little that human-affected soils (‘anthropic soils’) are relevance to the vast areas of the planet that were potential ‘golden spikes’ for the Anthropocene not experiencing industrialization at that time. In (Certini & Scalenghe 2011). However, these mar- other words, it does not coincide with a critical kers, together with their geomorphological coun- growth of human influence globally. Indeed, parts terparts, are essentially local or, at best, regional in of the world with some of the largest concentra- character, and are invariably time-transgressive tions of humanity, such as India and China, did (Gale & Hoare 2012). Moreover, with respect to not undergo their own industrial revolutions until the growth of urban centres, this is not a new the mid-twentieth century, some 200 years after phenomenon. Throughout the Middle and Late the AD 1750 trace-gas event in the ice cores. This Holocene, city states from the Punjab (the Harra- raises further doubts about the validity of the polar pan civilization), through the Fertile Crescent (the ice-core record as a potential GSSP for the base of Akkadian civilization) and Egypt, to the Mayan, the Anthropocene for, as we have already seen, Aztec and Inca cultures of Central and South any GSSP boundary should be a global one and, if P. L. GIBBARD & M. J. C. WALKER it is to be ratified by the IUGS, it must have around AD 1963 in sedimentary records (e.g. Good- worldwide applicability. site et al. 2001; Kemp et al. 2009). Both events In acknowledging these difficulties in the selec- have been proposed as potential global markers tion of an appropriate GSSP for the Anthropocene, for defining the onset of the Anthropocene (e.g. Zalasiewicz et al. (2011b) have suggested that an Zalasiewicz et al. 2008). However, although these alternative strategy might be to define the base are undoubtedly clear manifestations of human of the Anthropocene numerically with a GSSA impact on the terrestrial and climatic environment, (Global Standard Stratigraphic Age). At the level they simply mark one of many stages in human tech- of resolution sought (annual), and at this temporal nological development. They certainly do not distance, one possibility might be to select a numer- coincide with the onset of environmental changes ical age, such as the beginning of 1800 in the resulting from human activity, and therefore have Christian Gregorian . This would allow little value in defining the initiation of human simple and unambiguous correlation of the strati- impact (Gale & Hoare 2012). In passing, it is also graphical and historical records, as well as providing worth noting that radiogenic nuclide fallout was consistent utility and meaning to the currently used significantly lower in the Southern Hemisphere informal term. Should this proposal be deemed to than in the Northern Hemisphere, so the distinctive be of value to the Geoscience community, the weapons’ fallout peak is often difficult to discern in could be proposed as a GSSA to the ICS and sediment records from the Southern Hemisphere could then be ratified and given formal status by (e.g. Collins et al. 2001; Humphries et al. 2010). the IUGS. However, this compromise, although Furthermore, anthropogenic effects have not avoiding confusion regarding the onset of the only been manifest in the terrestrial sphere through- Anthropocene interval, would suffer the same out the Holocene, but may also have impacted on basic drawback as a GSSP, in that the basis for the atmospheric environment. For example, the the selection of age is a perceived acceleration of polar ice-core records show the first increase in human impact on the natural environment, which, CO2 concentrations c. 8000 years ago, while CH4 as we have already seen, is globally diachronous. concentrations began a similar rise c. 5000 years In other words, selecting an age such as 1800 is ago. The former has been related to forest clearance essentially a western perspective on world events, by human groups in China, India and Europe, while and the GSSA would have little meaning (or rel- the latter has been associated with expansion of rice evance) to those regions of Africa or Asia where farming and increasing livestock numbers (Ruddi- an increase in the pace of economic development man 2003, 2005; Ruddiman et al. 2011). A further did not occur until at least a century later. rise in CH4 concentrations in ice cores from the his- In terms of the second question posed above, torical period have been equated with long-term the palaeoenvironmental evidence suggests that increases in agricultural emissions and biomass humans have been shaping the global environment burning during the period of the Roman empire, to various degrees more or less throughout the the Han dynasty and the Medieval Climatic Anom- course of the Holocene and, to some extent, even aly, all of these records indicating that human before (e.g. Miller et al. 2005; Archibald et al. activity contributed to variations in both CO2 and 2012). This is clearly of considerable concern for CH4 emissions to the atmosphere in pre-industrial the archaeological community, who see a conti- times (Sapart et al. 2012). Indeed, the ice cores nuum of human/landscape interactions at a range also contain evidence of atmospheric heavy metal of temporal and spatial scales extending through pollution (As, Pb, Bi, Cu and Zn), reflecting smelt- the Holocene to the present day. Indeed, it has ing of lead and copper ores extending back to the been suggested that ‘by defining the Anthropocene Greek–Phoenician period (Krachler et al. 2009). as a geological epoch beginning only 200 years Similar records of atmospheric Pb pollution, reflect- ago, Crutzen and Stoermer truncate thousands of ing late prehistoric mining and smelting, have years of human interaction with the global envi- been obtained from peat sequences (Shotyk et al. ronment’ (Periman 2006, p. 558). Clearly, even 1998; Le Roux et al. 2004). These different lines younger events that have been suggested as base- of evidence are manifestations of a process of lines for the Anthropocene suffer from the same increasing human influence on the natural envi- difficulty. These include the ‘Great Acceleration’ ronment throughout the Holocene. Although no- of the second half of the twentieth century dur- one disputes the fact that there was a substantial ing which many human activities reached take-off amplification of human impact with the onset of points in terms of their environmental impacts the European Industrial Revolution, it is difficult (Steffen et al. 2011; Wolfe et al. 2012), and the to isolate a single horizon within the geological short-lived episode of nuclear bomb testing of the record that marks the global ‘tipping point’ where mid mid-twentieth century, which is reflected in a natural processes have been overtaken by human- radiogenic nuclide peak (in 14C and 137Cs) at induced environmental changes. FORMALIZING THE ‘ANTHROPOCENE’

The third question concerns the utility of defin- Conclusions ing a separate geological time unit, the Anthropo- cene. When considering a possible subdivision In order for the Anthropocene to be defined as a of the Holocene, the SQS/INTIMATE Working formal stratigraphical unit, a global event, distinct Group were concerned with putting forward a from that of the Holocene or of previous intergla- scheme that the geological community would find cial phases of the Pleistocene, must be identified useful and with which they would be comfortable on the basis of novel biotic (i.e. biostratigraphical), to operate. An extensive literature review showed sedimentary and geochemical change(s). Although quite clearly that the terms ‘Early’, ‘Middle (or there is unequivocal evidence in recent geolog- Mid-)’ and ‘Late’ Holocene were widely employed ical records of rapidly increasing anthropogenic in Holocene research, so by formalizing these impacts on natural environments and systems, it terms, the Working Group was effectively legiti- is uncertain whether the geological signature of mizing what was already custom and practice. these trends is sufficiently distinct, and adequately There is no doubt that the term ‘Anthropocene’ dated at the global scale, for a Holocene/Anthropo- has caught the popular imagination, as witnessed cene boundary to be substantiated on stratigraphic by the number of publications that have appeared in grounds. That being the case, if the term is to be recent years that incorporate the term; indeed, a new retained for the purposes of geological time divi- journal entitled Anthropocene is to be launched sion, it must remain informal. by Elsevier in 2013. However, the question remains As currently defined, we are living in the Holo- as to whether or not the utility of the term will be as cene Series or Epoch, the last 11.7 ka of Earth an informal designation for the period of recent history. Although, on strict geological grounds, enhanced human activity, or whether it can be this period can be considered to be the latest of a defined in a geological sense as a formal time- sequence of interglacials that have characterized stratigraphic unit of the GTS. At present, despite the Quaternary, and hence could be regarded as a the implicit geological connotation of the suffix unit of the Pleistocene Series/Epoch, the rise of ‘-cene’ implying a rank of Series/Epoch status, humans (Homo sapiens) to critical numbers and the usage of the term has been predominantly his- the increasing influence they have exerted on torical rather than geological in its application and natural systems provides the critical justification definition. Because the criteria initially used to for defining this period as a separate unit of justify a Holocene Series still obtain, and while Series/Epoch status within the GTS. As such, the fully accepting the profound and increasing influ- activities of humans cannot then be used again to ence of humanity on the natural environment over justify the definition of a discrete Anthropocene recent centuries, we remain firmly of the view that division. This is the view of many Holocene geo- the designation of the Anthropocene as a time unit scientists and archaeologists who do not accept equivalent to Series or Epoch divisions cannot yet that the Holocene has ended. be justified on stratigraphical grounds. At best, the Although there is a substantial popular move- Anthropocene might become another name for the ment towards the recognition of a new period that later Holocene (with a usage similar, perhaps, to acknowledges, and may indeed be characterized ‘Dark Ages’ or ‘Middle Ages’), but in a geological by, the overwhelming influence of humans on context the term would remain informal. Indeed, much of the natural environment, we continue to this view has now been reinforced by the Geolog- live within the same climatically and biologically ical Society of America, who have rejected the term defined time interval for which the term ‘Holocene’ from their 2012 Geological Time Scale because was proposed and formally ratified by the IUGS. it has no ‘internationally sanctioned standing’ (J. In the absence of a globally identifiable anthropo- D. Walker et al. 2012, p. 7). In many ways, our con- genic marker event that can be clearly recognized cerns are admirably expressed in a recent paper in a range of depositional contexts, that can be by Autin & Holbrook (2012), in which they write mapped in a conventional geological sense, and that can provide a consistent stratigraphic basis for Before we amend our stratigraphy and end the Holo- detaching the Anthropocene from the preceding cene, it would be best to settle the question of where Holocene, there is, in our view, no justification in the stratigraphic record to drive the golden spike for formally defining the Anthropocene as a new that defines when humanity became one of the preemi- stratigraphic unit (of whatever status) within the nent forces of nature. Even so, will finding this layer established geological timescale. lead to a globally relevant correlation? As stratigra- phers, we require criteria to map the Anthropocene with relevant and consistent meaning. Presently, we We are grateful to Prof. J. Lewin and Dr A. Smith for are left to map a unit conceptually rather than con- their helpful and insightful comments on an earlier ceptualizing a mappable stratigraphic unit. (Autin & version of the manuscript, and to one anonymous referee Holbrook 2012, p. 61) for a constructive critical review. We also thank the P. L. GIBBARD & M. J. C. WALKER editors of this volume for their invitation to us to present Gervais, P. 1867–69. Zoologie et ge´ne´rales: this paper on behalf of the Subcommission of Quaternary Nouvelles recherches sur les animaux verte´bre´s et fos- Stratigraphy, and for their encouragement and assistance siles. Paris. in preparing the final draft for publication. Gibbard,P.L.&Kolfschoten, VAN TH. 2005. Pleisto- cene and Holocene series. In: Gradstein, F., Ogg,J. & Smith, A. G. (eds) Geological Time Scale 2004. References Cambridge University Press, Cambridge, 441–452. Gibbard, P. L., Head,M.J. et al. 2010. Formal ratifica- AMERICAN COMMISSION ON STRATIGRAPHIC tion of the Quaternary system/period and the Pleisto- NOMENCLATURE 1961. Code of stratigraphic cene series/Epoch with a base at 2.58 Ma. Journal of nomenclature. Bulletin of the American Association Quaternary Science, 25, 96–102. of Petroleum Geologists, 45, 645–660. Goodsite, M. E., Rom,W.et al. 2001. High-resolution AMERICAN COMMISSION ON STRATIGRAPHIC AMS 14C dating of post-bomb peat archives of atmos- NOMENCLATURE 1970. Code of stratigraphic pheric pollutants. Radiocarbon, 43, 495–515. nomenclature, 2nd edn. American Association of Hedberg, H. D. (ed.) 1976. International Stratigraphic Petroleum Geologists Bulletin, 60, 1–45. Guide. John Wiley, London & New York. Archibald, S., Staver,C.&Levin, S. A. 2012. Evolution Heinzelin,J.DE & Tavernier, R. 1957. Flandrien. In: of human-driven fire regimes in Africa. Proceedings Pruvost, P. (ed.) Lexique Stratigraphique Inter- of the National Academy of Science, 109, 847–852. national. Paris, Centre National de la Recherche Autin,W.J.&Holbrook, J. 2012. Is the Anthropocene Scientifique, 1, 32. an issue of stratigraphy or pop culture? GSA Today, Humphries, M. S., Kindness,A.et al. 2010. 137Cs and 22, 60–61. 210Pb derived sediment accumulation rates and their Barnola, J. M., Anklin,M.et al. 1995. CO2 evolution role in the long-term development of the Mkuze during the last millennium as recorded by Antarctic River floodplain, South Africa. Geomorphology, 119, and Greenland ice. Tellus, 47B, 264–272. 88–96. Bender, M., Sowers,T.&Brook, E. 1997. Gases in Hyva¨rinen, H. 1978. Use and definition of the term Flan- ice cores. Proceedings of the National Academy drian. Boreas, 7, 182. of Sciences, 94, 8343–8349. Kemp, A. C., Horton,B.P.et al. 2009. Timing and Certini,G.&Scalenghe, R. 2011. Anthropogenic soils magnitude of recent accelerated sea-level rise (North are the golden spikes for the Anthropocene. The Holo- Carolina, United States). Geology, 37, 1035–1038. cene, 21, 1269–1274. Krachler, M., Zheng,J.et al. 2009. Global atmo- Chen, I.-C., Hill,J.K.et al. 2011. Rapid range shifts of spheric As and Bi contamination preserved in species associated with high levels of climate warm- 3000 year old Arctic ice. Global Biogeochemical ing. Science, 333, 1024–1026. Cycles, 23, GB3011, http://dx.doi.org/10.1029/2009 Collins, A. L., Walling,D.E.et al. 2001. Using 137Cs GB003471 measurements to quantify soil erosion and redistribu- Le Roux, G., Weiss,D.et al. 2004. Identifying the tion rates for areas under different land use in the sources and timing of ancient and medieval atmos- upper Kaleya River basin, southern Zambia. Geo- pheric lead pollution in England using a peat profile derma, 104, 299–323. from Lindow bog, Manchester. Journal of Environ- Crossland, C. J. (ed.) 2005. Coastal Fluxes in the Anthro- mental Monitoring, 6, 502–510. pocene. Springer, Berlin. Lourens, L., Hilgen,F.et al. 2005. The Neogene Crutzen, P. J. 2002. Geology of mankind. Nature, 415,23. period. In: Gradstein, F. M., Ogg,J.G.&Smith, Crutzen,P.J.&Stoermer, E. F. 2000. The Anthropo- A. G. (eds) A 2004. Cambridge cene. Global Change Newsletter, 41, 17–18. University Press, Cambridge, 409–440. Desnoyers, J. 1829. Observations sur un ensemble de Lowe,J.J.&Walker, M. J. C. 1997. Reconstructing de´poˆts marins. Annales des Sciences Naturelles Quaternary Environments. Longman, London. (Paris), 171–214, 402–491. Lyell, C. 1837. Principles of Geology, 5th edn. John Diamond, J. 2005. Collapse. Penguin, London & Murray, London. New York. Lyell, C. 1839. Nouveaux E´ le´ments de Ge´ologie. Pitois- Etheridge, D. M., Steele,L.P.et al. 1996. Natural and Levrault, Paris. anthropogenic changes in atmospheric CO2 over the MacFarling Meure, C. D., Etheridge,C.et al. last 1000 years from air in Arctic ice and firn. 2006. Law Dome CO2,CH4 and N2O ice core Journal of Geophysical Research, 101, 4115–4128. records extended to 2000 years BP. Geophysical Flint, R. F. 1971. Glacial and Quaternary Geology. John Research Letters, 33, L14810, http://dx.doi.org/10. Wiley, London & New York. 1029/2006GL026152 Forbes, E. 1846. On the connexion between the distri- Miller, G. H., Fogel,M.L.et al. 2005. Ecosystem bution of the existing fauna and flora of the British collapse in Pleistocene Australia and human role in Isles, and the geological changes which have affected megafaunal extinction. Science, 309, 287–290. their area, especially during the epoch of the Northern Morlot,A.VON 1854. U¨ ber die quaterna¨ren Gebilkde des Drift. Memoir of the Geological Survey of Great Thonegebeits. Verhandlingen der Schweizerisches Britain, 1, 336–432. Gesellschaftes geschichten Naturwetenschappen, 39, Gale,S.J.&Hoare, P. G. 2012. The stratigraphic status 161–164. of the Anthropocene. The Holocene, 22, 1491–1494, Morrison, R. B. 1969. The Pleistocene–Holocene bound- http://dx.doi.org/10.1177/0959683612449764 ary. Geologie en Mijnbouw, 48, 363–372. FORMALIZING THE ‘ANTHROPOCENE’

Nicholls, R. J., Wong,P.P.et al. 2007. Coastal systems Sowers, T. 2010. Atmospheric methane isotope records and low-lying areas. In: Parry, M. L., Canziani,O.F. covering the Holocene period. Quaternary Science et al. (eds) Climate Change 2007: Impacts, Adap- Reviews, 29, 213–221. tation and Vulnerability. Contribution of Working Steffen, W. A., Sanderson,P.D. et al. 2004. Global Group II to the Fourth Assessment Report of the Inter- Change and the Earth System: A Planet Under governmental Panel on Climate Change. Cambridge Pressure. Springer-Verlag, New York. University Press, Cambridge, 315–356. Steffen, W., Crutzen,P.J.&McNeil, J. R. 2007. The Nilsson, T. 1983. The Pleistocene. Reidel, Dordrecht. Anthropocene: are humans now overwhelming the Orr, J. C., Fabry,V.J.&Aumont, O. 2005. Anthropo- great forces of Nature? Ambio, 236, 614–621. genic ocean acidification over the twenty-first century Steffen, W., Grinevald,J. et al. 2011. The Anthropo- and its impact on calcifying organisms. Nature, 473, cene: conceptual and historical perspectives. Philoso- 681–686. phical Transactions of the Royal Society, London, Periman, R. D. 2006. Visualising the Anthropocene: A369, 842–867. human land use history and environmental manage- Urban, M. C., Tewsbury,J.J.&Sheldon, K. S. 2012. ment. In: Aguire-Bravo, C., Pellicane,P.J.et al. On a collision course: competition and dispersal dif- (eds) Monitoring Science and Technology Sympo- ferences create no-analogue communities and cause sium: Unifying Knowledge for Sustainability in the extinctions during climate change. Proceedings of the Western Hemisphere Proceedings RMRS-P-42CD. Royal Society of London, B279, 2072–2080. US Department of Agriculture, Forest Service, Rocky Walker, M., Johnsen,S. et al. 2009. Formal definition Mountain Research Station, Fort Collins, CO, and dating of the GSSP (Global Stratotype Section 558–564. and Point) for the base of the Holocene using the Reboul, H. 1833. Ge´ologie de la Pe´riode Quaternaire et Greenland NGRIP ice core, and selected auxiliary Introduction a l’Histoire Ancienne. F.G. Leverault, records. Journal of Quaternary Science, 24, 3–17. Paris. Walker, J. D., Geissman,J.W.et al. 2012. The Geologi- Remane, J., Bassett,M.G. et al. 1996. Revised guide- cal Society of America geologic time scale. Geological lines for the establishment of global chronostrati- Society of America Bulletin, 125, 259, http://dx.doi. graphic standards by the International Commission org/10.1130/B30712.1 on Stratigraphy (ICS). Episodes, 19, 77–81. Walker, M. J. C., Berkelhammer,M. et al. 2012. Rodiloco, F. 1970. Arduino (or Ardini), Giovanni. In: Formal subdivision of the Holocene Series/Epoch: a Gillespie, C. C. (ed.) Dictionary of Scientific Bibli- Discussion Paper by a Working Group of INTIMATE ography. Charles Scribner’s and Sons, New York, 1. (Integration of ice-core, marine and terrestrial records) Rosenbaum, M. S., McMillan,A.A.et al. 2003. Classi- and the Subcommission on Quaternary Stratigraphy fication of artificial (man-made) ground. Engineering (International Commission on Stratigraphy). Journal Geology, 69, 399–409. of Quaternary Science, 24, 3–17. Ruddiman, W. F. 2003. The anthropogenic greenhouse West, R. G. 1968. Pleistocene Geology and Biology, 1st era began thousands of years ago. Climatic Change, edn. Longman, London. 61, 261–293. West, R. G. 1977. Pleistocene Geology and Biology, 2nd Ruddiman, W. F. 2005. Plows, Plagues and Petroleum. edn. Longman, London. Princeton University Press, Princeton, NJ. West, R. G. 1979. Further on the Flandrian. Boreas, 8, 126. Ruddiman, W. F., Kutzbach,J.E.&Vavrus, S. J. 2011. Williams, M., Zalasiewicz,J.et al. 2011. The Anthro- Can natural or anthropogenic CO2 and CH4 increases pocene: a new epoch of geological time? Philosophical be falsified? The Holocene, 21, 865–879. Transactions of the Royal Sociey, London, 369A, Salvador, A. 1994. International Stratigraphic Guide, 833–1112. 2nd edn. International Union of Geological Sciences Wolfe, A. P., Hobbs,W.O.et al. 2012. Stratigraphic and Geological Society of America, Boulder, CO. expressions of the Holocene–Anthropocene transition Salvador, A. 2006a. The and the Quaternary revealed in sediments from remote lakes. Earth are here to stay. Association of American Petroleum Science Reviews, 116, 17–34. Geologists Bulletin, 90, 21–30. Woldstedt, P. 1969. Quarta¨r. F. Enke, Stuttgart. Salvador, A. 2006b. A stable Cenozoic geologic time Zalasiewicz, J., Smith,A.et al. 2004. Simplifying the scale is indispensable. Episodes, 29, 43–45. stratigraphy of time. Geology, 32,1–4. Sapart, C. J., Monteil,G. et al. 2012. Natural and Zalasiewicz, J., Smith,A.et al. 2008. Are we now anthropogenic variations in methane sources during living in the Anthropocene. GSA Today, 18,4–8. the past two millennia. Nature, 490, 85–88, http:// Zalasiewicz, J., Williams,M.et al. 2010. The new dx.doi.org/10.1038/nature11461 world of the Anthropocene. Environmental Science Schneer, C. J. 1969. Introduction. In: Schneer, C. J. (ed.) and Technology, 44, 2228–2231. Towards a History of Geology. The Massachusetts Zalasiewicz, J., Williams,M.et al. 2011a. The Anthro- Institute of Technology Press, Cambridge, MA & pocene: a new epoch of geological time. Philosophical London, 1–18. Transactions of the Royal Society, London, A369, Shotyk, W., Weiss,D.et al. 1998. History of atmos- 835–841. pheric lead deposition since 12 370 14C yr BP from a Zalasiewicz, J., Williams,M.et al. 2011b. Stratigra- Peat Bog, Jura Mountains, Switzerland. Science, 281, phy of the Anthropocene. Philosophical Transactions 1635–1640. of the Royal Society, London, A369, 1036–1055.