Researchers Are Hunting for Nuclear Debris, Mercury Pollution and Other

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HUMANS VERSUS EARTH other signsto define the Anthropocene, aproposed new geological Researchers are hunting for nuclear debris, mercury pollution and epoch that recognizes how people have transformed the planet. C at least 750 years ago, and then of European the settlers, began who Iroquoisthe people, cultivated who maize (corn) along lake’s the banks ing back nearly 1,000 years. In fidelity, high it has captured of evidence Layers of sediment accumulate like tree rings, creating an archive reach which leaves its bottom undisturbed by burrowing worms or currents. of epoch geological time.new in this lake could ground be zero for Anthropocene — the a potential that irreversibly started they transforming planet. the The mud layers designatinga signal moment the humans when achieved such power This lake is unusually for deep its its size so waters nevermix, fully are insearch of adistinctive marker mud inthe buried deep — is attracting attention from scientists around They globe. the in southern Ontario that inCanada hides something special waythe around its shore. But beneath its surface, pond this rawford it small just takes is so Lake 10minutes to stroll all ©

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A l l r i g h t s r e s e r v e d . - around theglobe. radionuclides blasts spread in 1945andlater of anuclearbomb The firstexplosion

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farming and chopping down trees more than five centuries later. Now, scientists are looking for much more recent, and significant, signs of

TIM PATTERSON upheaval tied to humans. Core samples taken from the lake bottom “should translate into a razor-sharp signal”, says Francine McCarthy, a micropalaeontolo- gist at nearby Brock University in St Cath- erines, Ontario, “and not one blurred by clams mushing it about.” McCarthy has been studying the lake since the 1980s, but she is looking at it now from a radical new perspective. Crawford Lake is one of ten sites around the globe that researchers are studying as potential markers for the start of the Anthropocene, an as-yet-unofficial designation that is being considered for inclusion in the geological time scale. The Anthropocene Working Group (AWG), a committee of 34 researchers formed by the International Commission on Stratigra- phy (ICS) in 2009, is leading the work, with the aim of crafting a proposal to formally recognize the Anthropocene. This new epoch would mark a clear departure from the Holocene, which started with the close of the last ice age. Researchers collect a sediment core from Crawford Lake to study possible markers of the Anthropocene. To define a new epoch, the researchers need to find a representative marker in the rock record geological record — that is, whether humans potential golden spikes, the radioactive record that identifies the point at which human activ- have left a distinctive set of marks preserved in from the nuclear age has emerged as the front ity exploded to such a massive scale that it left rock, seafloor mud or glacial ice that indicates a runner. “Radionuclides still look like the sharp- an indelible signature on the globe. fundamental change in the planet. est signal,” says Zalasiewicz. The AWG summed Given how much people have done to the After a decade of investigating this question, up its current work in The Anthropocene as a planet, there are many potential markers. “Sci- the AWG decided in May that humans had, in Geological Time Unit, published in February by entifically, in terms of evidence, we’re spoiled fact, left an indelible geological mark. In a bind- Cambridge University Press. for choice, but we have to pin it down,” says Jan ing vote in May, 29 of the 34 members opted to Crawford Lake has serious competition Zalasiewicz, a palaeobiologist at the University move forward with developing a proposal sup- in the contest to become the location for the of Leicester, UK, and chair of the AWG. porting the designation of the Anthropocene. golden spike. Colin Waters, a geologist at the The committee’s current plan is to look to The AWG’s next task is to put forward a University of Leicester and AWG secretary, is the legacy of the atomic age, when radioactive formal proposal identifying a global boundary coordinating research teams that are studying debris from mid-twentieth-century nuclear stratotype section and point (GSSP), or ‘golden a reservoir in California, an ice core from Ant- bomb blasts left a fingerprint of radioiso- spike’ (see C. N. Waters et al. Earth Sci. Rev. 178, arctica, cave deposits in northern Italy, coral topes in the atmosphere, rocks, trees and even 379–429; 2018). A GSSP is a primary geological reefs in the Caribbean and Australia, and a peat humans. “There’s a big bomb spike somewhere marker at one location that can be correlated bog in Switzerland, among other sites. All will between 1952 and 1954 that is quite distinct with sites around the globe in diverse environ- be testing for the radionuclide signal, most and unmistakable,” says Zalasiewicz. ments. The Anthropocene’s golden spike needs probably carbon-14 and the long-lived isotope Once they pick their representative marker, to demonstrate that there was a globally syn- plutonium-239, as well as for secondary mark- researchers working with the AWG need to chronous moment when physical, chemical ers ranging from persistent organic pollutants gather enough evidence from around the and biological processes amounted to the irre- and microplastics to fly ash from coal burning. world to convince the governing bodies of versible crossing of a geological threshold from Despite the long list of potential sites and geoscience that they have found a truly reli- the Holocene to something altogether different. markers, progress has been slow. “The geologi- able signal for the start of the Anthropocene. In its recent vote, the AWG members decided cal time scale is a tool that is used by all geolo- But some scientists argue that human activity overwhelmingly to pursue a GSSP in the mid- gists around the world,” says Martin Head, has been shaping the planet for thousands of twentieth century. This time marks the start of an Earth scientist at Brock University and an years, and that the working group has settled the ‘Great Acceleration’, a vast transformation AWG member, “so it’s very important that too quickly on the 1950s for the start of the after the Second World War when the grow- gratuitous changes don’t occur. Any change proposed epoch. Erle Ellis, a geographer at the ing population began consuming resources should be very, very carefully considered.” University of Maryland, Baltimore County, and creating completely new materials at an and an AWG member, has criticized the com- exponential rate, eclipsing even the Industrial QUEST FOR THE GOLDEN SPIKE mittee’s plans for designating the start of the Revolution. All that activity poured unprec- The quest for a golden spike leads back to those Anthropocene. “The AWG decided the tim- edented amounts of persistent organic pollut- variegated layers beneath the still waters of ing of the boundary before deciding on the ants into the environment, ramped up the rate Crawford Lake. McCarthy is collaborating with marker, not the other way around,” says Ellis. of animal extinctions and created geological researchers elsewhere in Canada and around features that had never before existed. These the world to analyse core samples from 1940 to HARD EVIDENCE include 4-kilometre-deep gold mines and 1965, the years bordering peak nuclear fallout In the end, it will be the rocks that have the landfills more than 70 metres high, such as along with the onset of the Great Acceleration. final say. The decision on whether to officially Teufelsberg in Berlin, where rubble from the A laboratory in Zurich in Switzerland is designate the Anthropocene will come down Second World War was piled into an artificial testing for the primary marker of radionuclides, to stratigraphic evidence preserved in the hill. Although the AWG is still exploring several and a team in London is looking for other

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its mandate is to make decisions based on the stratigraphic record alone. Not everyone is convinced it can do that yet. One sore point is that the working group made a decision on when to set the boundary, even though it had not yet settled on a golden spike ULLSTEIN BILD VIA GETTY ULLSTEIN in the stratigraphic record. “It is an imposi- tion of ideas onto matter, shaping evidence to fit, but it should be the other way around,” says Matt Edgeworth, an archaeologist at the University of Leicester. Edgeworth is a member of the AWG but voted against the decision to recognize the Anthropocene. One concern is that the radio nuclide signal, although it will persist for 100,000 years, will weaken as the radioactive elements decay. “In geological terms, where most boundaries in time are millions of years old,” argues Edgeworth, “that is not a very durable marker.” Other critics, notably William Ruddiman, a palaeoclimatologist at the University of Virginia in Charlottesville, have pushed for starting the Anthropocene when humans In post-war Berlin, rubble was piled into a hill that became known as Teufelsberg, or Devil’s Mountain. first began terrascaping Earth with agricul- ture thousands of years ago, or when they signals, such as surging concentrations of fly lead a team analysing an ice core from the wiped out the megafauna of Australia and ash, to see if they are all synchronous. A group Antarctic Peninsula. The human signals of North America many millennia before 1950 led by Tim Patterson at Carleton University in radionuclides, along with heavy metals and (see W. F. Ruddiman Prog. Phys. Geogr. Earth Ottawa, Canada, will be measuring the abun- fly ash particles, have been found even on this Environ. http://doi.org/gd4shx; 2018). Some dance of testate amoebae — single-celled micro- remote continent. Her team will also analyse have argued against designating the Anthro- organisms surrounded by a shell that persists for temperature, snow accumulation, carbon diox- pocene at all, given that the Holocene has been thousands of years. Populations of these amoe- ide and methane, which all changed markedly marked by escalating human influences since bae explode, often to the detriment of other in the mid-twentieth century, although per- the end of the last ice age. species, when nutrients from human habita- haps not precisely in sync with the bomb spike. Zalasiewicz readily acknowledges that tion and agricultural run-off provide excessive human impacts are well recognized throughout nourishment. Researchers at Brock University A SERIES OF VOTES much of the Holocene, but the scale of global will search for microplastics that could have Like the stratigraphic record that the change since the start of the Great Acceleration, arrived by water, by wind on airborne fibres, or researchers are studying, the decision to offi- along with the sudden introduction of com- even with insects that had cially designate the Anthro- pletely new substances to the planet, are wholly ingested them. pocene is multilayered. unprecedented. “When I first started this work, At another candidate site, The AWG aims to present I thought that the Anthropocene as a geological Searsville Lake in Califor- a final proposal identifying unit might fall apart, because everything would nia’s San Francisco Bay area, “SCIENTIFICALLY, a mid-twentieth-century be wishy-washy and just a gradation,” he says, a team is testing for radio- GSSP to its parent body, “but in fact, it has sharpened up.” nuclides along with other IN TERMS the Quaternary Subcom- Although Edgeworth questions the single proxies of human influence. mission of the ICS, by 2021. mid-twentieth-century marker, he does not They will examine sediment OF EVIDENCE If approved, the proposal deny that our species has altered the globe. samples from the lake bot- will be voted on by the ICS “I see first-hand the enormous impact that tom to identify changes in WE’RE SPOILED and will then proceed to humans are continuing to have on surface land use in the region as well the executive committee strata,” he says. “It is almost as though a new as increasing amounts of FOR CHOICE.” of the International Union layer, geologically speaking, is forming on the lead and mercury pollution. of Geological Sciences surface of the Earth.” “We hope to create a real (IUGS) for final ratifica- Max Berkelhammer, an Earth scientist at ‘motion picture’ of the Bay Area over the last tion. Only if it passes all these hurdles will the the University of Illinois at Chicago who is century to millennium,” says Elizabeth Hadly, a Anthropocene officially become a new unit of not involved in the current debate, but whose biologist at nearby Stanford University and one the International Chronostratigraphic Chart, research contributed to the designation of the of the principal investigators at the Searsville more commonly known as the Geological Time Holocene, defends the AWG’s conclusions. “It’s site. But, for the purposes of the Anthropocene Scale. So far, all 65 GSSPs that have been ratified hard to say that what’s been happening in the designation, she and other researchers would are from marine environments, except for the twentieth century is just another manifesta- need to find a clear golden spike around 1950 one marking the start of the Holocene, which tion of what’s been happening over the last few that signals a distinct leap in human activity uses a Greenland ice core. thousand years,” he says. “The scale of change that also lines up with what other candidate The formal process has moved much more is so much larger. And it’s difficult to imagine sites across the globe are finding. slowly than has popular culture, which has reversing course.” ■ Meanwhile, in the Southern Hemisphere, already embraced the Anthropocene and used Liz Thomas, a palaeoclimatologist at the Brit- the term on everything from record albums Meera Subramanian is a freelance journalist ish Antarctic Survey in Cambridge, UK, will to magazine covers. But the AWG is clear that in Cape Cod, Massachusetts.

CORRECTION The News Feature ‘Humans versus Earth’ (Nature 572, 168–170; 2019) incorrectly located the groups doing some work on samples from Crawford Lake. The testate amoebae work was done by a group at Carleton University and the microplastics work .was done at Brock University.