Feature Bulletin of the Atomic Scientists 2015, Vol. 71(3) 46–57 ! The Author(s) 2015 Reprints and permissions: Can nuclear weapons fallout sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0096340215581357 mark the beginning of the http://thebulletin.sagepub.com Anthropocene Epoch? Colin N. Waters, James P. M. Syvitski, Agnieszka Gałuszka, Gary J. Hancock, Jan Zalasiewicz, Alejandro Cearreta, Jacques Grinevald, Catherine Jeandel, J. R. McNeill, Colin Summerhayes, and Anthony Barnosky Abstract Many scientists are making the case that humanity is living in a new geological epoch, the Anthropocene, but there is no agreement yet as to when this epoch began. The start might be defined by a historical event, such as the beginning of the fossil-fueled Industrial Revolution or the first nuclear explosion in 1945. Standard strati- graphic practice, however, requires a more significant, globally widespread, and abrupt signature, and the fallout from nuclear weapons testing appears most suitable. The appearance of plutonium 239 (used in post- 1945 above-ground nuclear weapons tests) makes a good marker: This isotope is rare in nature but a significant component of fallout. It has other features to recommend it as a stable marker in layers of sedimentary rock and soil, including: long half-life, low solubility, and high particle reactivity. It may be used in conjunction with other radioactive isotopes, such as americium 241 and carbon 14, to categorize distinct fallout signatures in sediments and ice caps. On a global scale, the first appearance of plutonium 239 in sedimentary sequences corresponds to the early 1950s. While plutonium is easily detectable over the entire Earth using modern meas- urement techniques, a site to define the Anthropocene (known as a Ògolden spikeÓ) would ideally be located between 30 and 60 degrees north of the equator, where fallout is maximal, within undisturbed marine or lake environments. Keywords Anthropocene, golden spike, nuclear weapons fallout, radioactive isotope, radiogenic signature, Trinity test eventy years agoÑat 5:30 a.m. on flash of light and heat, and a roaring shock July 16, 1945Ñthe worldÕs first wave that took 40 seconds to reach the S nuclear device exploded at the closest observers, a fireball rose into the Trinity Test Site in what was then the sky, forming a mushroom cloud 7.5 miles Alamogordo Bombing and Gunnery high. J. Robert Oppenheimer later wrote Range in New Mexico. After an intense that he and other Manhattan Project Waters et al. 47 scientists who had gathered to watch the Industrial Revolution, or some other test Òknew the world would not be the major shift that left its mark on the geo- same.Ó The Ònuclear ageÓ had begun logical record. One recent paper argues (Ackland and McGuire, 1986; Eby et al., for either 1610 (when atmospheric 2010; Groves, 1962). carbon dioxide levels dipped after the Arguably, Trinity was also the begin- arrival of Europeans brought death to ning of something even bigger: a new about 50 million native people in the geological epoch (Zalasiewicz et al., Americas) or 1964 (based on peak 2015). Human activities have had such a carbon 14 fallout signatures) as potential great impact upon the Earth that many kickoff dates (Lewis and Maslin, 2015). researchers suggest we are no longer But if geoscientists want to establish a living in the Holocene Epoch (a term starting point for the Anthropocene, Tri- describing the most recent slice of geo- nity and the nuclear bombings and tests logical time that literally means Òentirely that followed it from 1945 to the early newÓ), but instead within a brand-new 1960s created an extremely distinctive time unit: the Anthropocene, from the radiogenic signatureÑa unique pattern Greek words for ÒhumanÓ and Ònew.Ó of radioactive isotopes captured in the Since 2009, a small group of us, com- layers of the planetÕs marine and lake posed of geoscientists and other experts sediments, rock, and glacial ice that can from across the globe, have assembled to serve as a clear, easily detected book- develop a proposal for this new termin- mark for the start of a new chapter in ology and to make recommendations to our planetÕs history. the official bodyÑknown as the Interna- Does it really matter what epoch tional Commission on StratigraphyÑthat we are living in? ItÕs obviously important determines geological time units. To to geologists and other Earth scientists, accomplish this, our panel, the Anthropo- who use the geological timescale to meas- cene Working Group, has not only been ure, describe, and compare events and examining the evidence for the Anthro- changes that happened in our planetÕs poceneÕs existence but attempting to past. For many people outside these determine the duration of this potential fields, though, the potential designation new unit (Zalasiewicz et al., 2012). The of a new epoch has political overtones. group will also make recommendations As an editorial in a leading scientific jour- about where the Anthropocene, if it nal observed a few years ago, the Anthro- does exist, fits into the hierarchy of geo- pocene Òreflects a grim reality on the logical time: period, epoch, or age (per- ground, and it provides a powerful frame- haps even within the Holocene Epoch). work for considering global change and Many scientists agree that the Earth how to manage itÓ (Nature, 2011). has left the Holocene behind and is now Although the Anthropocene has, in in the Anthropocene, but there is less the public sphere, become closely agreement about when the Anthropo- associated with climate change and par- cene began. Some researchers make ticularly the burning of fossil fuels, it is good arguments for dating the beginning much bigger than that. We and other sci- of this new epoch to the advent of entists who are considering whether a agriculture, or to the increase in fossil new epoch has begunÑand if so, how fuel consumption that ushered in the best to mark its onsetÑare examining a 48 Bulletin of the Atomic Scientists 71(3) host of environmental changes wrought Anthropocene: the range of globally by humans, from the domestication of extensive and abrupt signatures during plants and animals to the nuclear arms the mid-20th century (Waters et al., race. Public discussion of these changes 2014) that coincide with the ÒGreat can only lead to a growing awareness AccelerationÓ of population growth, eco- that humans have left an enormous nomic development, industrialization, footprint on the EarthÑand not just a mineral and hydrocarbon exploitation, carbon oneÑand may help increase the manufacturing of novel materials public understanding of how a warming such as plastics, the emergence of mega- climate relates to other momentous cities, and increased species extinctions global changes. and invasions (Steffen et al., 2007, 2015). Some researchers even suggest that the Origins of the Anthropocene onset of the Anthropocene is marked by a ÒdiachronousÓ boundary in sedi- In the geological timescale used by Earth mentsÑone in which a boundary between scientists, the Holocene Epoch began human-modified and ÒnaturalÓ ground about 11,700 years ago, after the planetÕs can be found that is of different ages at last glacial phase came to an end. When different locationsÑand thus is not a geo- the Anthropocene concept (Crutzen, logical time unit (Edgeworth et al., 2015). 2002; Crutzen and Stoermer, 2000) was The standard accepted practice for initially proposed, the Industrial Revolu- defining geological time units during tion was suggested as its starting point. the current eon (which began about 541 The reasoning was that industrializa- million years ago) is to identify a single tionÕs accelerated population expansion, reference point (or Ògolden spikeÓ), at a technological changes, and economic specific location, that marks the lower growth caused increased urbanization, boundary of a succession of rock layers mineral exploitation, and crop cultiva- as the beginning of the time unit. This tion; these factors in turn elevated atmos- internationally agreed-upon physical pheric carbon dioxide and methane reference point is representative of the concentrations enormously (Waters sum of environmental changes that jus- et al., 2014; Williams et al., 2011). tify recognition of the time unitÑthe Alternatively, the proponents of an appearance or extinction of a fossil spe- Òearly AnthropoceneÓ or ÒPalaeoan- cies, say, or a geochemical signature left thropoceneÓ interval that preceded the by a massive volcanic eruption (Smith, Industrial Revolution (Foley et al., 2013) 2014). For example, the boundary emphasize that this interval had a diffuse between the Cretaceous and Paleogene beginning, with signatures associated Periods has as its golden spike the base with the onset of deforestation, agricul- of an iridium-enriched layer of rock in El ture, and animal domestication; some Kef, TunisiaÑa marker for the debris scientists propose that these changes spewed into the atmosphere when a broadly coincide with the beginning huge meteorite struck the Earth and for of the existing Holocene Epoch (Smith the mass extinctions of dinosaurs and and Zeder, 2013). other creatures that followed that event. But there is growing evidence for The mid-20th century saw substantial another, later starting point for the changes to living things and their Waters et al. 49 ecological relationsÑalso known as burning of coal and other fossil biotic changes (Barnosky, 2014)Ñbut fuels, initially beginning during the those changes have not yet been well Industrial Revolution