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Part 1: Anthropocene Series/Epoch: stratigraphic context and justification of rank The Anthropocene Epoch and Crawfordian Age: proposals by the Anthropocene Working Group
Summary
This paper by the Anthropocene Working Group proposes formally defining the Anthropocene as a new geological epoch, marked by human-caused changes starting around the 1950s. Among the stratigraphic signals used to define this era, microplastics are listed as a key marker, alongside nuclear fallout and synthetic chemicals. The inclusion of microplastics as a defining feature of a geological epoch underscores just how widespread and permanent plastic pollution has become in Earth's systems.
The Anthropocene Working Group (AWG) has concluded that the Anthropocene represents geological reality and should be linked with the plethora of stratigraphic proxies that initiate or show marked perturbations at around the 1950s, and should be defined using a Global boundary Stratotype Section and Point (GSSP). We propose formalizing the Anthropocene as series/epoch, terminating the Holocene Series/Epoch with a single Crawfordian stage/age. The GSSP should be located at the level where the primary marker shows a rapid increase in 239+240Pu concentrations (coinciding with a globally recognisable, isochronous signal of the first above-ground thermonuclear tests). The stratigraphic signature of the Anthropocene comprises: a) lithostratigraphic signals, including many new proxies, such as synthetic inorganic crystalline mineral-like compounds, microplastics, fly ash and black carbon, in addition to direct modification through human terraforming of landscape and indirect influences on sedimentary facies through drivers such as climate change; b) chemostratigraphic signals including inorganic and organic contaminants and isotopic shifts of carbon and nitrogen; c) fallout from above-ground nuclear weapons testing; d) stratigraphic effects of climate warming, sea-level rise and ocean acidification; and e) biostratigraphic signals, especially range and abundance changes characterised by unprecedented rates and extents of non-native species introductions, increased population and species extinction and extirpation rates. These correlative markers are present in many kinds of geological deposits around the world. This ubiquity of signals verifies that the Anthropocene can be widely delineated as a sharply distinctive chronostratigraphic unit in diverse terrestrial and marine depositional environments, and reflects a major Earth System change that will have geologically lasting consequences. As background, the Anthropocene was suggested as a new epoch by Paul Crutzen in 2000. The AWG was established in 2009 by the Subcommission on Quaternary Stratigraphy to examine the evidence for the potential inclusion of the Anthropocene in the International Chronostratigraphic Chart (ICC) and, if warranted, to formulate a definition and proposal. Various suggested start dates were considered, and the mid-20th century was found to be the only one associated with an extensive array of effectively globally isochronous geological markers reflecting the ‘Great Acceleration’ of population, industrialization and globalization. Alternative interpretations of the Anthropocene, including as an informal ‘event’, were considered in detail by the AWG and found to be inconsistent with the stratigraphic evidence.