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Humans have dramatically and irrevocably altered the face of the Earth through our activities. Climate change has accelerated the melting of glaciers and tipped the balance of chemicals in the atmosphere. We’ve driven animals to extinction and dug really deep holes. All these changes, some scientists argue, mean that we’ve entered a new geological epoch — the age of humans or the Anthropocene. We’re living in it now, but when did it start?
A handful of dates have been proposed, but in a new paper published in Nature, two researchers argue that two rise above the rest.
Somewhere on the schoolroom walls of your youth probably hung a poster with a stack of rainbow or earth-toned layers representing the ages of the Earth. They have solid, important-sounding names — Cambrian, Jurassic, Paleocene — and you learned that they correspond to layers of rock and the fossils contained within. Maybe you remember that the Holocene, that sliver at the end of the stack, is the name given to our epoch. Unlike a lot of other geological ages, the relative recent start of the Holocene allows us to give it a very precise start, writes Richard Monastersky for Nature News. He writes about the work of Michael Walker, a researcher at the University of Wales Trinity St David in Lampeter, U.K.:
Walker and his colleagues selected a climatic change — the end of the last ice age's final cold snap — and identified a chemical signature of that warming at a depth of 1,492.45 meters in a core of ice drilled near the centre of Greenland. A similar fingerprint of warming can be seen in lake and marine sediments around the world, allowing geologists to precisely identify the start of the Holocene elsewhere.
The Anthropocene Working Group—29 experts from the International Union of Geological Sciences—are now looking for a similarly precise way to pin down the start of the Anthropocene. And the debate is vigorous, Monastersky writes.
In the new paper, two researchers not from the A.W.G. examined many of the proposed dates — for example, the origin of farming around 11,000 years ago — but tossed most of them out because they didn’t correspond to a change that happened at the same time around the globe, reports Robbie Gonzalez for io9. The two dates they favor are 1610 and 1964.
The year 1964 is visible in rock layers as a spike in radioactive isotopes from nuclear-weapons testing. As for 1610, Michelle Nijhuis explains for The New Yorker:
The year 1610 is distinguished in Antarctic ice cores by a dip in atmospheric carbon dioxide. In the decades after the Europeans—and their germs—arrived in the Americas, some fifty million people died; huge swaths of abandoned farmland reverted to forest, and the trees absorbed more carbon than the crops.
The earlier date is the stronger candidate, the researchers conclude. One of the authors, Simon Lewis, explains in statement from University College London:
Historically, the collision of the Old and New Worlds marks the beginning of the modern world. Many historians regard agricultural imports into Europe from the vast new lands of the Americas, alongside the availability of coal, as the two essential precursors of the Industrial Revolution, which in turn unleashed further waves of global environmental changes. Geologically, this boundary also marks Earth’s last globally synchronous cool moment before the onset of the long-term global warmth of the Anthropocene.
The date isn’t official — that will be decided when the A.W.G. makes recommendations to the International Commission on Stratigraphy next year. But whether 1964, 1610 or some other date ends up marking the start of the Anthropocene, they all fall relatively close in the geological record. What is inescapable is the fact that we see a need to name it. "It is geologists saying, 'We are witnesses to this profound and problematic transition,'" Naomi Oreskes, a science historian and A.W.G. member told The New Yorker. "And we want the world to talk about it."