Definition of the Anthropocene: a view from the underworld
Ian J. Fairchild, Silvia Frisia, 2014. "Definition of the Anthropocene: a view from the underworld", A Stratigraphical Basis for the Anthropocene, C. N. Waters, J. A. Zalasiewicz, M. Williams, M. Ellis, A. M. Snelling
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Annually laminated stalagmites from natural caves and limestone mines capture a number of significant environmental and climatic signals during the anthropogenically disturbed era. The effects of forest clearance, or development of agricultural or industrial practices, can be marked by changes in soil or hydrological responses leading to shifts in both chemical (e.g. carbon and oxygen isotope ratios or trace elements) and physical (e.g. fabric, thickness of laminae) signals. However, these signals are diachronous because of the spatial heterogeneity of human societies. Twentieth-century changes in atmospheric composition are known from speleothems at several sites and demonstrate pollution disturbance of the sulphur cycle and the signal provided by the 1950s rise in radiocarbon caused by atmospheric nuclear tests. This latter is a global signal and hence a strong candidate to define the start of the Anthropocene, although other considerations, including comparison with instrumental archives, would favour an earlier timing. An attractive option is the climate amelioration marking the end of the Little Ice Age in the mid-nineteenth century, which is marked in Alpine and other Northern Hemisphere areas. Examples are illustrated from the Grotta di Ernesto cave to illustrate the appearance of a putative mid-nineteenth-century boundary.
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Humankind has pervasively influenced the Earth’s atmosphere, biosphere, geosphere, hydrosphere and cryosphere, arguably to the point of fashioning a new geological epoch, the Anthropocene. To constrain the Anthropocene as a potential formal unit within the Geological Time Scale, a spectrum of indicators of anthropogenically-induced environmental change is considered, and shown as stratigraphical signals that may be used to characterize an Anthropocene unit, and to recognize its base. This volume describes a range of evidence that may help to define this potential new time unit and details key signatures that could be used in its definition. These signatures include lithostratigraphical (novel deposits, minerals and mineral magnetism), biostratigraphical (macro- and micro-palaeontological successions and human-induced trace fossils) and chemostratigraphical (organic, inorganic and radiogenic signatures in deposits, speleothems and ice and volcanic eruptions). We include, finally, the suggestion that humans have created a further sphere, the technosphere, that drives global change.