4–5). Other terms to denote humans as an agent of global change were proposed in the early 20th century. From the 1920s to 1940s, for example, some European scientists referred to the Earth as entering an anthropogenic era known as the “noösphere” ( Teilhard de Chardin, 1966 and Vernadsky,

this website 1945), signaling a growing human domination of the global biosphere (see Crutzen, 2002a and Zalasiewicz et al., 2008, p. 2228). Stoppani, Teilhard de Chardin, and Vernadsky defined no starting date for such human domination and their anthropozoic and noösphere labels were not widely adopted. Nonetheless, they were among the first to explicitly recognize a widespread human domination of Earth’s systems. More recently, the concept of an Anthropocene found traction when scientists, the media, and the public grappled with the growing recognition that anthropogenic influences are now on scale with some of the major geologic

events of the past (Zalasiewicz et al., 2008, p. 2228). Increased concentrations of atmospheric greenhouse gases and the discovery of the ozone hole over Antarctica, for example, PCI 32765 led to increased recognition that human activity could adversely affect the functioning of Earth’s systems, including atmospheric processes long thought to be wholly natural phenomena (Steffen et al., 2011, pp. 842–843). Journalist Andrew Revkin (1992) referenced the Anthrocene in his book on global climate change and atmospheric warming and Vitousek et al.’s (1997)Science paper summarized human domination of earth’s ecosystems. It was not until Crutzen and Stoermer (2000; also see Crutzen, 2002a and Crutzen,

2002b) explicitly proposed that the Anthropocene began with increased atmospheric carbon levels caused by the industrial revolution in the late 18th century (including invention of the steam Dichloromethane dehalogenase engine in AD 1784), that the concept began to gain momentum among scientists and the public. Geological epochs are defined using a number of observations ranging from sediment layers, ice cores, and the appearance or disappearance of distinctive forms of life. To justify the creation of an Anthropocene epoch as a formal unit of geologic time, scientists must demonstrate that the earth has undergone significant enough changes due to human actions to distinguish it from the Holocene, Pleistocene, or other geological epochs. As justification for the Anthropocene concept, Crutzen (2002a) pointed to growing concentrations of carbon dioxide and methane in polar ice, rapid human population growth, and significant modification of the world’s atmosphere, oceans, fresh water, forests, soils, flora, fauna, and more, all the result of human action (see also Crutzen and Steffen, 2003 and Steffen et al., 2011). The Anthropocene concept has been increasingly embraced by scholars and the public, but with no consensus as to when it began.