A transparent framework for defining the Anthropocene Epoch

Abstract

Lewis and Maslin (2015) applied modern geological requirements to a systematic search for evidence of markers that could be used to define a new geological time unit, the Anthropocene Epoch. These must include (1) a near-permanent change to the Earth System that sets it on to a new trajectory and (2) global changes to the Earth System recorded in a number of stratigraphic deposits worldwide to provide a correlative boundary event or marker called a Global Stratotype Section & Point (GSSP) or ‘golden spike’. Using this framework Lewis and Maslin conclude that just two time periods likely adhere to the criteria. These are the irreversible cross-ocean exchange of species alongside the globally synchronous coolest part of the ‘Little Ice Age’ in the 17th century, marked by the 1610 minima of CO2 (Orbis Spike), or the accelerating atmospheric, oceanic and terrestrial changes in the second half of the 20th century, conveniently marked by the 1964 peak radionuclide fallout (Bomb Spike). Two recent responses by members of the Anthropocene Working Group (Zalasiewicz, 2015a, 2015b) to Lewis and Maslin (2015) do not dispute the GSSP framework, nor that these are the only two time periods that minimally fit the requirements for a new epoch. Instead they question our selection of two specific 1610 and 1964 GSSP primary markers. We respond to their misconceptions and misunderstandings about geological criteria and relevant evidence required to define a GSSP. Our primary goal, however, is to present a framework to assist the scientific community in objectively and transparently arriving at a robust selection of a GSSP and correlated markers to define the Anthropocene Epoch.