A new geological period? Defining the Anthropocene and Environmental Archaeology

by Tony Brown and Andy J Howard

There is growing discussion and concern within the palaeoenvironmental community regarding the designation of a new geological period, which recognises the profound impact that modern humans have had since the end of the last glaciation and continue to have on natural ecosystems (Zalasiewicz et al., 2010; 2011).

However, defining the basal geological boundary of this new age, termed informally in the literature as the ‘Anthropocene’ is not as easy as it might appear, as has recently been discussed in relation to geomorphology by Brown et al. (2013a). The point of this short article is to bring this debate to the attention of environmental archaeologists and highlight questions which they might want to consider. With an understanding of natural processes, vegetation histories and human impact, environmental archaeologists are in a unique position to contribute to this debate through publication of empirical evidence in Environmental Archaeology. Should the Anthropocene be designated a geological Epoch and the boundary set at an arbitrary year, either in the European industrial revolution (e.g. 1850 AD) or at the spike of artificial radionuclides (c. 1950 AD), then this both terminates and arguably alters the status of the Holocene and especially the late Holocene sensu Walker et al. (2012). There are perhaps three general headings under which environmental archaeologists might contribute data and consider the ramifications of the proposal.

1) Land-use change and agriculture
Brown Technically in order to be a geological period there must be a change in the rock-record (Hedberg, 1976). We do see this as fine grained sediments stored within alluvial systems together with organic rich deposits preserved in palaeochannels provide a record of changing climatic conditions, vegetation histories and human activity, which can be securely dated using a range of radiometric techniques. Studies throughout Europe published in a range of journals have identified a major discontinuity between deposits laid down under the climate conditions of the last ‘Ice Age’, hunter-gatherer landscapes and those laid down in response to agricultural activity during the later Holocene. However, absolute dating demonstrates that this boundary is time transgressive and spans a period of around 4000 years in the mid to Late Holocene (Brown et al., 2013b). One such example of the spatial and temporal complexity of human activity is highlighted in the recent paper in Environmental Archaeology by Woodbridge et al. (2012, 17.1). Some researchers have suggested the term ‘ago-industrial alluvium’ to describe distinctive metal-contaminated deposits datable to the mid 18th and 19th centuries in northern Britain and suggest it can be used as a regional land use -climate marker for the Anthropocene (Foulds et al., 2013); evidence from south west Britain published by Brown et al. in Environmental Archaeology indicates that the record of metal mining can extend back considerably further (2009, 14.1). Indeed the more we investigate alluvial systems in the Old World the more we recognise early effects of agriculture and/or mining. A recent example of the former is evidence from Central Africa of alluvial response to farming as early as the mid-Holocene (Lespez et al., 2011) and an example of the latter is the widespread recognition of pre-Roman mining in the Iberian peninsula (Peraza, 2013). More examples are emerging from Africa but the evidence for agricultural impact in these regions is complicated by the role of animal herding within the palaeoeconomy; a special issue of Environmental Archaeology on the ‘Bioarchaeology of Animal Dung’ (Marinova et al., 2013, 18.1) demonstrates the insights that can be provided by such material, which in turn, may help to provide a better understanding of animal husbandry and stimulate further research within this field. Similarly, there are few examples from the river valleys of south east Asia or the pre-European Americas, although the paper in Environmental Archaeology by Fuller and Qin Ling considering the emergence of rice cultivation and its links to changing social and environmental parameters provides significant insights into our regional knowledge of the former region (2010, 15.2).

Since alluvial sequences cannot provide a single chronological datum for the Anthropocene, researchers are looking to other possible golden spikes to define its start. Some researchers favour definition based on the rise in global temperatures caused by greenhouse gas emissions resulting from industrialisation; others suggest using the baseline set by nuclear weapons emissions at 1950 since even pre-industrialised areas of the world record this event in lacustrine deposits (Wolfe et al., 2013). Some archaeologists have already begun to address these questions at a global scale (Fuller et al., 2011; Kaplan et al., 2009) and these attempts clearly show the magnitude of human land use change even if the effect on pre-industrial atmospheric chemistry is still not agreed, including the Ruddiman hypothesis (Ruddiman, 2003, 2005; Singarayer et al., 2011).

2) Agriculture and evolution
kenwardtipperThere is, however, another question intimately connected with environmental archaeology. Since it is routine practice to definegeological periods by reference to the ‘fossilised’ record of life on Earth an obvious record of change is floral and faunal evolution and in particular the impact on new bilogical forms and also the abundance of such forms. In the case of the Holocene this would include: the replacement of wild species by domesticates; the rise of synanthropic species; and the rise of humans as a species (and associated burials, some of which will survive). Some might argue that, seen from a geological perspective, this could also include the extinction of the Pleistocene mega-fauna, although this is increasingly being seen as a more drawn out and regionally variable process (Barnosky et al., 2004). Environmental Archaeology has published a number of papers that contribute to this broad theme (for example, Kenward and Tipper, 2008, 13.1; Albarella et al., 2009, 14.2; Robinson, 2013, 18.2).

3) Material culture
Archaeological sub-division of time stems from the technologically based 3-Age System (see Daniel, 1943) and it has frequently been suggested that a post-industrial age could be defined upon plastic or synthetic materials reflecting the rise of petrochemical industries (Zalasiewicz et al., 2011). Similarly, the massive expansion of urbanisation and associated infrastructure development is leaving a signature of stratigraphic horizons likely to remain in the geological record. Archaeologists who excavate in urban contexts are of course acutely aware of the time-depth that typically underlies such areas often indicative of a continuity of occupation rather than a great discontinuity. Likewise the vast modern areas associated with extractive industries and ‘made ground’ have been proposed as a new geological horizon (Price et al., 2011). It could be argued that this again fails to recognise how this is just the acceleration of a trend and although positive globally, it can be locally negative.

Implications and Comments
It is worthwhile reflecting that whatever the status of the Anthropocene it cannot be truly comparable with any past geological boundaries which had non-human driving processes. It is therefore not surprising that there are many different perspectives that could be taken on these questions. The Holocene might be regarded as a period of transition from the Pleistocene to the Anthropocene, or the Anthropocene might be regarded as a sub-stage of the Holocene. Equally given the progressive and unique nature of this transformation, the Anthropocene might be regarded as a completely new supra-geological if not archaeological/anthropological period. The purpose of this short article has been to draw the attention of environmental archaeologists to this debate, reference some of the key literature, and to encourage discussion and contributions from the sub-discipline. It is indeed entirely feasible that archaeologists might argue that the question lies in their ‘academic patch’ and that the data they have on both the transformation of both abiotic and biotic components of earth surface systems is critical to the debate. The contribution which environmental archaeologists can make within multi-disciplinary research teams should generate key evidence that would be welcomed for publication by Environmental Archaeology.