Geology's Timekeepers Are Feuding - The Atlantic - 0 views
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, in 2000, the Nobel Prize-winning chemist Paul Crutzen won permanent fame for stratigraphy. He proposed that humans had so throughly altered the fundamental processes of the planet—through agriculture, climate change, and nuclear testing, and other phenomena—that a new geological epoch had commenced: the Anthropocene, the age of humans.
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Zalasiewicz should know. He is the chair of the Anthropocene working group, which the ICS established in 2009 to investigate whether the new epoch deserved a place in stratigraphic time.
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In 2015, the group announced that the Anthropocene was a plausible new layer and that it should likely follow the Holocene. But the team has yet to propose a “golden spike” for the epoch: a boundary in the sedimentary rock record where the Anthropocene clearly begins.
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Officially, the Holocene is still running today. You have lived your entire life in the Holocene, and the Holocene has constituted the geological “present” for as long as there have been geologists.But if we now live in a new epoch, the Anthropocene, then the ICS will have to chop the Holocene somewhere. It will have to choose when the Holocene ended, and it will move some amount of time out of the purview of the Holocene working group and into that of the Anthropocene working group.
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This is politically difficult. And right now, the Anthropocene working group seems intent on not carving too deep into the Holocene. In a paper published earlier this year in Earth-Science Reviews, the Anthropocene working group’s members strongly imply that they will propose starting the new epoch in the mid-20th century.
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Some geologists argue that the Anthropocene started even earlier: perhaps 4,000 or 6,000 years ago, as farmers began to remake the land surface.“Most of the world’s forests that were going to be converted to cropland and agriculture were already cleared well before 1950,” says Bill Ruddiman, a geology professor at the University of Virginia and an advocate of this extremely early Anthropocene.
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“Most of the world’s prairies and steppes that were going to be cleared for crops were already gone, by then. How can you argue the Anthropocene started in 1950 when all of the major things that affect Earth’s surface were already over?”Van der Pluijm agreed that the Anthropocene working group was picking 1950 for “not very good reasons.”“Agriculture was the revolution that allowed society to develop,” he said. “That was really when people started to force the land to work for them. That massive land movement—it’s like a landslide, except it’s a humanslide. And it is not, of course, as dramatic as today’s motion of land, but it starts the clock.”
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This muddle had to stop. The Holocene comes up constantly in discussions of modern global warming. Geologists and climate scientists did not make their jobs any easier by slicing it in different ways and telling contradictory stories about it.
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This process started almost 10 years ago. For this reason, Zalasiewicz, the chair of the Anthropocene working group, said he wasn’t blindsided by the new subdivisions at all. In fact, he voted to adopt them as a member of the Quaternary working group.“Whether the Anthropocene works with a unified Holocene or one that’s in three parts makes for very little difference,” he told me.In fact, it had made the Anthropocene group’s work easier. “It has been useful to compare the scale of the two climate events that mark the new boundaries [within the Holocene] with the kind of changes that we’re assessing in the Anthropocene. It has been quite useful to have the compare and contrast,” he said. “Our view is that some of the changes in the Anthropocene are rather bigger.”
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Zalasiewicz said that he and his colleagues were going as fast as they could. When the working group group began its work in 2009, it was “really starting from scratch,” he told me.While other working groups have a large body of stratigraphic research to consider, the Anthropocene working group had nothing. “We had to spend a fair bit of time deciding whether the Anthropocene was geology at all,” he said. Then they had to decide where its signal could show up. Now, they’re looking for evidence that shows it.
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This cycle of “glacials” and “interglacials” has played out about 50 times over the last several million years. When the Holocene began, it was only another interglacial—albeit the one we live in. Until recently, glaciers were still on schedule to descend in another 30,000 years or so.Yet geologists still call the Holocene an epoch, even though they do not bestow this term on any of the previous 49 interglacials. It get special treatment because we live in it.
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Much of this science is now moot. Humanity’s vast emissions of greenhouse gas have now so warmed the climate that they have offset the next glaciation. They may even knock us out of the ongoing cycle of Ice Ages, sending the Earth hurtling back toward a “greenhouse” climate after the more amenable “icehouse” climate during which humans evolved.For this reason, van der Pluijm wants the Anthropocene to supplant the Holocene entirely. Humans made their first great change to the environment at the close of the last glaciation, when they seem to have hunted the world’s largest mammals—the wooly mammoth, the saber-toothed tiger—to extinction. Why not start the Anthropocene then?He would even rename the pre-1800 period “the Holocene Age” as a consolation prize:
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Zalasiewicz said he would not start the Anthropocene too early in time, as it would be too work-intensive for the field to rename such a vast swath of time. “The early-Anthropocene idea would crosscut against the Holocene as it’s seen by Holocene workers,” he said. If other academics didn’t like this, they could create their own timescales and start the Anthropocene Epoch where they choose. “We have no jurisdiction over the word Anthropocene,” he said.
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Ruddiman, the University of Virginia professor who first argued for a very early Anthropocene, now makes an even broader case. He’s not sure it makes sense to formally define the Anthropocene at all. In a paper published this week, he objects to designating the Anthropocene as starting in the 1950s—and then he objects to delineating the Anthropocene, or indeed any new geological epoch, by name. “Keep the use of the term informal,” he told me. “Don’t make it rigid. Keep it informal so people can say the early-agricultural Anthropocene, or the industrial-era Anthropocene.”
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“This is the age of geochemical dating,” he said. Geologists have stopped looking to the ICS to place each rock sample into the rock sequence. Instead, field geologists use laboratory techniques to get a precise year or century of origin for each rock sample. “The community just doesn’t care about these definitions,” he said.