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Anthropocene Since ≈150 ago? Hadean | 4.6 billion years ago Eon Period

Phanerozoic | 542 million years ago

Archean | 3.8 billion An Epoch Debate years ago on October 7, 2011 www.sciencemag.org Downloaded from Proterozoic | 2.5 billion years ago

There’s no dispute that humans are leaving their mark on the planet, but geologists and other scientists are debating whether this imprint is distinctive and enduring enough to designate a new epoch: the Anthropocene

“Each I see it, it’s dramatic; the equiv- the major transitions in ’s . It is fi fth mass extinction event, wiping out more alent of listening to a particularly impres- the location for a “golden spike,” an interna- than 60% of marine life. sive bit of Mozart—like the opening of tionally agreed-on marker for the boundary Now, scientists say, the planet has crossed Don Giovanni, or the bit where Don gets between two different geological periods, another geological boundary, a transforma- dragged down to the pits,” says geologist Jan , or epochs. In this case, the golden spike tion that will leave its own signature stripe Zalasiewicz of the University of Leicester in marks the boundary between the Ordovician in the rocks—and humans are the change- the United Kingdom. and Silurian periods, two planetary states so makers. An infl uential group of geologists, The object of his awestruck tone seems different from each other that, to geologists, ecologists, and biologists argue that humans unremarkable: a stripe of black rock abut- the rocky evidence for each is clearly dis- have so changed the planet that it is entering ting a pale gray section of cliff in Dob’s Linn tinguishable. The Ordovician ended some another phase of geological time, called the gorge in the United Kingdom. But to geol- 445 million years ago as rapid glaciation and Anthropocene, “the Age of Man.” Human-

ogists, this slice of shale represents one of other global changes triggered the planet’s ity, they contend, can be considered a IMAGE) (EARTH NASA CREDIT:

32 7 OCTOBER 2011 VOL 334 SCIENCE www.sciencemag.org NEWSFOCUS

geophysical force on a par with supervolca- we’re trying to do is to ask how different is Although humans have changed Earth’s noes, asteroid impacts, or the kinds of tec- our current world from that of a prehuman biota and its hydrology through damming tonic shift that led to the massive glaciation equivalent. And to what extent is the present rivers, creating reservoirs, sucking dry aqui- of the Ordovician. state of the planet and its various changes fers, and melting glaciers, the geologists “The Dob’s Linn golden spike marks a in biology, chemistry, geography converted who will ultimately judge the Anthropocene revolutionary period in the Earth’s history,” into ?” he says. case may end up focusing more on altera- Zalasiewicz says. “I feel quite the same The Anthropocene debate is continuing tion of the planet’s lithosphere, its rocky sense of awe when I think about the kinds next week at the 2011 Geological Society shape. Some suggest that humanmade infra- of large-scale geological changes that we are of America conference in a session chaired structure will fashion a unique and endur- making to our planet now.” by Stanley Finney, a geologist at California ing strata. “In the eyes of a geologist, we’re From the invention of agriculture and State University, Long Beach, who is the making really quite interesting patterns out domestication of animals to the creation of current chair of the International Commis- of our raw materials,” Zalasiewicz says. cities, humans have been altering the land- sion on Stratigraphy. Finney is one of the “Wherever a road was buried, it would look scape ever since the Holocene epoch began outspoken skeptics of the Anthropo- like a rather strange and distinctive fossil 11,500 years ago at the end of the last ice cene designation. He agrees that humans are river channel, but one which is quite rectan- age. But, until recently, people have only changing the planet but questions how much gular in shape and with a particular pattern changed their local environments. The of a mark will be left in the strata. “Many of gravel and other materials like concrete industrial revolution increased the extent of our visible impacts could be removed that are not typical of river channels. Mil- and reach of our impact, making it truly through erosion,” he says. lions of years from now, a geologist would global. And after World War II, the system- see this and raise an eyebrow. A lot that 3.8 billion wide human effect on our planet accelerated The writing in the rocks we’re producing is distinctive.” dramatically to the extent that the human- Erle Ellis, an ecologist at the University of Cities, too, would leave their marks. wrought changes may be considered com- Maryland, Baltimore County, comes down Some may erode away, but others, particu- parable, many scientists say, to geological firmly on the side of designating a new larly those like Amsterdam or New Orleans transformations of the past, like that of the epoch, a view colored by his investigations that are in low-lying coastal zones and could on October 7, 2011 Ordovician to the Silurian. into how humans have altered the plan- become “fossilized” as sediments accumu- It was Nobel laureate Paul Crutzen et’s land covering. Ellis, a member of the late over them, would leave their signatures who fi rst came up with the term “Anthro- Anthropocene Working Group, calculates of foundations, plumbing, and rubble in the pocene.” In an article in Nature in 2002, that 80% of Earth’s land surface has been lithostrata. “Peel back the pavements and Crutzen argued that human changes have modifi ed by humans, with about 40% cur- the human interventions are already writ in moved the planet out of the Holocene into a rently being used to produce food—a fi gure the rocks,” says Simon Price, an urban geo- much less climatically stable age. The notion that doesn’t include scientist with the British Geological Survey. took hold. A wide range of scientists have land used for tim- Online “We’re witnessing a geological process, but

used the term to describe our unprecedented, ber plantations. it’s by our hands, not by glaciers or rivers.” www.sciencemag.org sciencemag.org planetwide environmental effects, some of Such deforestation Podcast interview Humans are changing the lithostratig- which are immediately obvious from satel- and conversion to with author raphy in now easily visible ways. Mining lite images of Earth. But formally accepting cropland or savanna Vince. and other excavations remove four as the Anthropocene as a geological term is a leaves clear signs much sediment as the world’s glaciers and more controversial matter. After all, changes in the geological record; palynologists, who rivers move each , and massive land- that appear vast from our human perspec- study pollen , can date human- forming projects have created entire islands tive might be invisible on a geological time kind’s ancient agricultural forays with great in the United Arab Emirates and elsewhere. Downloaded from scale. And debates over designating a new accuracy. The current unprecedented rate of Other anthropogenic changes are not epoch, era, or period can take decades— deforestation—80,000 km2 per year—will obvious from Google Earth but will leave even centuries—to resolve. also be easy to spot in the rock record, Ellis an enduring legacy. Long-lasting alterations In 2009, the International Commission says. There are now more trees in agricul- to the planet’s chemistry are already evi- on Stratigraphy, the body charged with for- tural land than in forests. dent: The world is currently being fl ooded mally designating geological time periods, The human impact on biodiversity will with light carbon (the C-12 isotope rather decided the Anthropocene concept “has infl uence the types and dispersal of fossil than C-13) due to fossil-fuel burning, and some merit.” It set up the Anthropocene remains. “Biostratigraphy is a very effec- there is now a measurable difference—con- Working Group, chaired by Zalasiewicz, tive way of recognizing one’s place in deep sistent around the world—in the carbon to investigate the proposed age and report time,” Zalasiewicz says. Consider that more composition of biological specimens such back. This February, members of the group than 90% of total vertebrate biomass today as sea shells, coral, and the shells of plank- published their initial fi ndings in a special is made up of humans and domesticated ton foraminifera, which will be preserved issue of the Philosophical Transactions of animals, up from 0.1% 10,000 years ago. in the strata. Chemostratigraphy will also the Royal Society A. The group reported a And if the prediction of some biologists reveal the appearance of novel chemicals, wide range of human impacts on the planet comes true, Earth will experience the sixth such as PCBs, plastics, radioactive isotopes that will leave a stratigraphically signifi cant mass extinction event in its 4.5-billion-year like cesium from atomic tests (see sidebar, mark on the geological record. history because of hunting, overfi shing, hab- p. 37), and newly common materials, from Although he may often sound like an itat loss, pollution, and climate change; that metals such as aluminum (which doesn’t nat- Anthropocene convert, Zalasiewicz says he would offer another, sobering piece of evi- urally appear in its elemental state) to nitrates hasn’t offi cially made up his mind. “What dence for the Anthropocene. Continued on page 37

www.sciencemag.org SCIENCE VOL 334 7 OCTOBER 2011 33 NEWSFOCUS A Global Perspective on the Anthropocene

Ever since humans launched Sputnik WATER into space, we’ve been able to observe Growth of U.S. Dams and Reservoirs our planet and its changes from a truly global perspective. Satellites and 1850 1900 improved data collection and analysis have allowed scientists to measure the anthropogenic infl uence on a range of Earth systems, enabling researchers to track rates of deforestation in the Ama- zon, Arctic ice melt, trails of air pollu- tion, the extent of sea-level rise, and many other regional and global phenom- ena. These tools are enabling scientists to look at human changes to the planet’s 1950 2000 atmosphere, hydrology, lithosphere, and biota—and infer which changes are pro- found enough to be measurable millions of years hence. on October 7, 2011

SOURCE: JAMES P. M. SYVITSKI ET AL., PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A 369, (2011)

1 2 3 4 5 Humans are increasingly exerting Getting More Acidic Aragonite saturation state control over Earth’s fresh water, through reservoirs, dams, and canals. And as atmospheric carbon dioxide (currently at 392 ppm) increases, the

ocean is becoming more acidic, as shown www.sciencemag.org by the decreasing saturation state of aragonite (right). Aragonite is a type of calcium carbonate that many ocean creatures use to build their shells. CO2 280 PPM CO2 450 PPM AIR SOURCE: O. HOEGH-GULDBERG ET AL., SCIENCE 318, 5857 (14 DECEMBER 2007)

We can’t directly see many of the Atmospheric CO2 Concentration vs. Human Population 380 changes we’ve made to our atmosphere, 6 Downloaded from 360 although we can measure the chemical pol- 5 lutants and isotopic changes. Indirectly, 340 though, we can feel the global warming 4 effect of releasing increasing amounts of 320

c o nc e nt r a t i n ( p m ) 300 3

carbon dioxide into the air. 2

280 2

260 H u m a n p o la t io ( b illio s ) 1 240 A t mo sp h e r i c C O 0 5000 3000 1000 500 B.C.E. 1 C.E. 500 1000 1500 2000 Year SOURCE: JED O. KAPLAN ET AL., THE HOLOCENE 21, 5 (AUGUST 2011)

% Ozone Depletion Over Antarctica Atmospheric N2O Concentration PPMV Atmospheric CH4 Concentration PPMV 70 310 1750 60 50 300 1500 40 290 1250 30 20 280 1000 10 0 270 750 1750 1800 1850 1900 1950 2000 1750 1800 1850 1900 1950 2000 1750 1800 1850 1900 1950 2000 SOURCE: WILL STEFFEN ET AL., PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A 369 (2011)

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LAND Anthropogenic Transformation of the Terrestrial Biosphere

YEARS OF Intensive Use >8000 years 5000–8000 3000–5000 2000–3000 1000–2000 500–1000 250–500 100–250 < 100

Wild NO HISTORY OF USE Woodlands Grasslands & steppe Shrublands Desert & tundra

Seminatural NO HISTORY OF USE Moderate use (>500 years)

CREDIT: ERLE ELLIS, ADAPTED FROM E. ELLIS, PROCEEDINGS OF THE ROYAL SOCIETY A, 369:1010 (2011)

Perhaps the most obvious mark we’ve , Deep Erosion: Who Erodes Land Faster? made to the planet is in land-use 1000 on October 7, 2011 changes. For millennia, humans have 100 chopped down forests and moved rock and soil for agriculture and pastureland—and 10 7.2 more recently, for construction. 1.0 billion tons/year Human-induced erosion 0.1 Mean rate of erosion 0.01 from natural processes o n e s f a u l lo ( b illio ) T

1000 100 10 www.sciencemag.org Years (C.E. 2000) LIFE SOURCE: BRUCE H. WILKINSON, GEOLOGY 33, 3 (MARCH 2005)

Humans have boosted numbers of % Worldwide Fisheries Fully Exploited Domesticating the Planet “useful” species such as cattle while 100 depleting others through hunting, overfi sh- 80 ing, habitat loss, or invasive competition. 60

Some scientists believe humans will cause the Downloaded from 40 Consider that 90% planet’s sixth mass extinction: Average species of total mammalian abundance of 3000 wild populations 20 biomass is made up declined 40% between 1970 and 2000. 0 of humans and 1950 1960 1970 1980 1990 2000 domesticated animals SOURCE: WILL STEFFEN ET AL., PHILOSOPHICAL TRANSACTIONS … OF THE ROYAL SOCIETY A 369 (2011) The Fall of the Wild 120

100

80 Marine species … up from Terrestrial species 0.1% 10,000 years ago. Freshwater species S pe c i e s a bu n da 60 All vertebrate species

40

1970 2000 1975 1980 1985 1990 1995 VACLAV SMIL, THE EARTH’S BIOSPHERE: EVOLUTION, SOURCE: WORLD WIDE FUND FOR NATURE AND UNEP WORLD CONSERV. MONITORING CENTER DYNAMICS, AND CHANGE. MIT PRESS (2002)

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A Sign of Our Times If we are living in a new geological phase called the Anthropocene, when did it begin? In other words, where does its golden spike belong? Many human-driven planetary changes have their roots in the indus- trial revolution, when the human population reached 1 billion. Atmo- spheric carbon dioxide from fossil fuels started to build from around 1800, although it probably took 50 to 100 years before new concen- trations of light carbon accumulated in measurable levels in marine shells. That change could be the marker for the golden spike designat- ing the beginning of the Anthropocene. There is a precedent: The bound- ary between the Paleocene and the Eocene epochs of the Cenozoic era is based on a change of carbon isotope chemistry. But the scale of our impact accelerated rapidly after 1945 when popu- lation doubled (from 3 billion in 1950 to 6 billion by 2000). As a result, some think the golden spike—offi cially known as a Global Boundary Stra- Reading the rocks. A geologist marks the totype Section and Point—should “golden spike” of the Ordovician-Silurian be set around 1945, which hand- boundary at Dob’s Linn, Scotland, where a ily provides a marker that’s sud- darker stripe in the shale reveals the fi rst den, distinctive, and global: appearance of graptolite fossils (inset). the introduction of radioactive nuclei into the environment from Zalasiewicz says, because millions of years the first atomic-bomb tests in in the future, with error bars of thousands Alamogordo, New Mexico. “The of years, that kind of distinction will be impossible to perceive. Events that on October 7, 2011 golden spike could be put into a look abrupt in the strata may have taken millions of years to occur, and layer of accumulating lake sedi- many changes take time to reveal themselves. For example, the tempera- ments in which the radioactive ture rise at the beginning of the Holocene was fairly abrupt, but it still took cesium fi rst appears,” geologist some 5000 years for sea-level rise to catch up. Jan Zalasiewicz of the University “The golden spike we choose would be a time boundary that we use of Leicester in the United King- with full knowledge that most changes on Earth are happening in different Explosive signal. The atomic bomb dom says. places at different times,” Zalasiewicz says. ”It’s useful and instructive to tests of 1945 produced a sudden From a geological perspec- think of [the Anthropocene] from the far future perspective, but in practice

dispersal of radioactive dust that can tive, it doesn’t matter whether the we’re dealing with it today. So we have to adopt as precise a time scale as www.sciencemag.org be measured globally. spike is at 1800, 1945, or 2050, we can.” –G.V.

Continued from page 33 logical time scale is to the Anthropocene. tute in Canberra. “Different eras and epochs (which humans have made abundant through In 100,000 years from now, people will not be in the past have been defi ned by changes fertilizer production and fossil-fuel burning). digging the strata to fi nd out about the world in climate and biodiversity. We’re already The nitrates in agricultural runoff also as it was in 2011, he argues; there are far better experiencing both of these, and for the fi rst Downloaded from cause the massive dead zones that currently tools for that. Geologists now and in the future time we are aware of doing so and actually affect 250,000 km2 of the world’s oceans. will use the human and the many driving these changes.” Similar zones have been recorded in the cultural records that are kept in order to look Zalasiewicz’s working group is aiming planet’s paleontological record, and the back to this time. The Anthropocene may be a to deliver a final report at the 2016 Inter- current ones likely will be as well. Ocean useful general term, Finney says, but it has no national Geological Congress in South acidification, too, is a measurable result place on the offi cial stratigraphic time scale. Africa. But there’s unlikely to be a quick of anthropogenic carbon emissions being Ellis disagrees. “It’s really helpful and rel- vote then on whether the Anthropocene dissolved in the oceans—they are now evant to think like a geologist, even though deserves the title of epoch—or period or age. more acidic than at any time in the past I’m not one. It frames our impacts on a big- The Ordovician-Silurian boundary at Dob’s A; © D K L I M T E / CO R BI S ( N ) ; A P G ES 800,000 years or more. ger planetary perspective. To be able to look Linn was finally agreed on in 1986, more back at the rocks and say, ‘Something hap- than a century after its proposal by geolo- Challenging tradition pened here that cannot be explained by any- gist Charles Lapworth. Only about half of AK A K UW The working group is still gathering evi- thing other than human impact’ is really the major boundaries in the Phanerozoic— dence that human changes such as these powerful,” Ellis says. our current geological eon covering the past will leave an enduring legacy, then they will “I think we’re challenging the traditional 542 million years—have been fi xed; the rest assess it and decide whether the Anthropo- view that geology always looks backwards. are still being argued over. Geologists, like cene should be formalized on the geological Geology is happening all around us now at a their subject, are resistant to rapid change. time scale, and if so, at what level: an age, rate that we can certainly discern,” says Will –GAIA VINCE epoch, era, or a period. Steffen, executive director of the Australian Gaia Vince writes on environmental issues in the devel-

C R E DI T S ( O P BO M ) : Y H I Finney questions how relevant the geo- National University’s Climate Change Insti- oping world at wanderinggaia.com.

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