NEWSFOCUS Anthropocene Since ≈150 years ago? Hadean | 4.6 billion years ago Eon Era Period Epoch 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 time I see it, it’s dramatic; the equiv- the major transitions in Earth’s history. 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 eras, 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) NASA (EARTH 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 geology?” 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 most 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 Gaia Vince. and other excavations remove four times 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 year, and massive land- that appear vast from our human perspec- study pollen paleontology, 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.