THE HUMAN LAYER - ANTHROPOCENE ERA...¿

THE HUMAN LAYER

Is humanity’s impact on its environment so huge that the planet has entered a new geological era: the Anthropocene? The idea is gaining ground—and dividing scientists. Helen Gordon investigates

From INTELLIGENT LIFE magazine, November/December 2015

“CONCRETE IS A new kind of rock…We’ve made about 500 billion tonnes of it, which is enough for one kilo for every square metre of the Earth’s surface, land and sea.”

In the summer of 2015 Jan Zalasiewicz, professor of palaeobiology at the University of Leicester, was speaking at the Tate Modern as part of the Anthropocene Project conference. Concrete, he explained, can be considered a characteristic deposit of the Anthropocene Epoch just as coal is of the Carboniferous Period.

Leaving the stage Zalasiewicz quickly found himself at the centre of a crowd of artists and curators who wanted to talk about the Anthropocene. Men in black-framed glasses and women with Jean Seberg haircuts discussed tectonic forces, millennial time and the infrastructural unconscious of contemporary urbanism. The Otolith Group, Turner prize-nominated artists, showed a film about a Californian woman who claims to be able to predict earthquakes and Dipesh Chakrabarty, a historian, suggested that “the term…invites you to place human beings in the context of deep time.”

Anthropos: “human being”. Kainos: “new”. In 2000 Paul Crutzen, an atmospheric chemist, and Eugene Stoermer, a biologist, crystallised a radical idea that had been floating around: humankind’s impact on the Earth’s ecology has been so profound that it is fashioning an entirely new geological epoch. The change is being wrought not just by concrete and plastic but also by soaring extinction rates and changes to the carbon cycle, the nitrogen cycle and temperature. The Holocene Epoch, according to this theory, is finished: we have entered the Anthropocene.

The term’s power derives from the intellectual heft it borrows from an academic discipline, geology. By measuring humanity’s planetary influence on a geological timescale, it implies an impact vaster than empires, though not more slow. It carries in its tail familiar narratives of planetary disaster and the looming threat of extinction.

The term has spread rapidly from the sciences through the arts and out into popular culture: there is a graphic novel, several death-metal albums, a Brian Eno track and an “Anthropocene Fashion” Pinterest site board. Yet its air of authority is misleading, for the Anthropocene has no formal scientific status. Among geologists there is no consensus as to when, or indeed whether, it began; it is a source of disagreement and, to some, embarrassment.

THE EARTH HAS existed for 4.6 billion years. For convenience, geologists divide this span into units of time: ages, epochs, periods, eras and eons. Some of the periods are familiar: Jurassic, Carboniferous. But a list of ages—Wordian, Roadian, Kungurian—sounds more like the roll call for some intergalactic council meeting in the Alpha Centauri system. Divisions between units are based on the occurrence of “significant” events that leave a changed world and a record of this change in the strata (layers of rocks or occasionally ice). The Pleistocene/Holocene division is a global-warming event that can be seen as a sudden change in the composition of trapped air in the Greenland ice cores. The Cretaceous/Paleogene division is the mass extinction of some three-quarters of plant and animal species, including all non-avian dinosaurs. Evidence from the rocks might include a radically altered fossil record. “Geology is often a forensic science,” said Zalasiewicz. “It’s Sherlock Holmes stuff basically.”

Right now we are living in the Holocene Epoch, in the Quaternary Period, in the Cenozoic Era, in the Phanerzoic Eon. Geological units are hierarchical and nest inside one another like matryoshka dolls. An “epoch” is defined by relatively minor geological change and typically covers between 2m and 30m years. Eons, by contrast, are massive. All of geological time is divided into only four eons. The most recent, the Phanerozoic, covers the last 540m years and the significant event that led to its creation was the beginning of multicellular life.

The branch of geology that concerns itself with the classification of layers of rock (or ice) is known as stratigraphy. By building up a picture of the layers of strata you build up a history of the Earth and, eventually, a geological timescale. Today the official version of that timescale is known as the International Chronostratigraphic Chart, produced by the International Committee on Stratigraphy (ICS). The result of centuries of painstaking work by thousands of geologists, it provides an organising structure that supports all studies of the Earth’s past. “It’s the one thing you’ll find in every professional geologist’s office,” a friend who lectures in Earth sciences told me. “It’s the equivalent of the periodic table.” This is the chart that would need to be amended should the Anthropocene be formally accepted.

THE HUMAN LAYER

Used to working with timescales of thousands, millions and billions of years, stratigraphers are not famously impulsive. In their discipline, “BP” stands for “years Before the Present”, and the “Present” is defined as 1950. According to ICS guidelines any new boundary definition must be left in place for a minimum of ten years before amendments are allowed, and proposals relating to changes to geological units involve a lengthy, hierarchical procedure. Zalasiewicz chairs the Anthropocene Working Group, the official body that must debate whether the term “Anthropocene” is (a) scientifically justified and (b) useful to the scientific community as a formal unit. If the answers are yes, then a summary paper will be handed to the Subcommission on Quaternary Stratigraphy (SQS). If the SQS are in agreement, the proposal will be passed up the chain to the ICS. If accepted by the ICS it will be sent finally to the International Union of Geological Sciences for formal ratification.

The Working Group was set up in 2009 and now has more than 30 members drawn from around the world. In 2014 they published a collection of papers: “A Stratigraphical Basis for the Anthropocene”. In 2016 they hope to present one or two summary papers to the ICS. Plenty of jokes have been made about the work proceeding on a “geological time scale” but for the traditional stratigraphers this feels more like break-neck speed: the haggling over older divisions of the timescale often lasts for decades.

EARLIER THIS YEAR I travelled to Leicester to speak with Zalasiewicz. In addition to his day job he writes popular science books and is translating the work of 18th-century French naturalist the Comte de Buffon. “I think about the 18th- and 19th-century naturalists and how they came at everything fresh. We come at it with clutter, with all this bloody education,” he said. For Zalasiewicz the Anthropocene is, among other things, an opportunity to see anew what has always been in front of us. “We can look at buildings, for example, and say that they are also part of the rock cycle. They are made of rocks and will go back to being rocks. They will leave a distinctive record.”

We drove out through the suburbs of Leicester to an old railway cutting. Tall nettles and purple-flowering willowherb grew in the shade of a steep tree-lined bank. One hundred and eighty-five million years ago, during the Early Jurassic, we would have been standing on the floor of the shallow sea that covered the whole of Britain. Today that sea floor has been translated into a sandy-coloured limestone rock filled with fossils: brachiopods, ammonites and belemnites. Also preserved are the tracks and burrows of floor-dwelling organisms. These are what are known as “trace fossils” or “ichnofossils”—not the organism itself but a mark it left behind. Considered one way the London Underground system (or the New York Subway, or the Tokyo Metro) is a giant trace fossil. Another type of trace fossil is what Zalasiewicz calls a “technofossil”—the fossilised trace of a manufactured product. A paleolithic flint axe might become a technofossil, so might a double-decker bus or a toothbrush. Zalasiewicz was excited: “One thing we want to pursue is, what is the true diversity of techno-fossils? Has anybody ever counted how many different types of toothbrush have been made?”

One hundred and eighty-five million years from now, what else might be preserved from our own time? What evidence discoverable in the rocks? Suggestions include changes to the fossil record (this organism stopped existing; this one suddenly appeared on the other side of the world); anthropogenic deposits (sediments containing manmade materials such as metals, plastics, glass); evidence of anthroturbation (underground holes and tunnels dug by humans); the altered composition of air trapped inside ice cores. From a stratigrapher’s point of view what matters is not that humans are leaving an imprint but that the Earth system is changing. Humans just happen to be important geological drivers of that change.

We walked farther along the cutting. Here, shelly limestone stopped about a metre from the floor; above it was a shale, very dark blue-grey and composed of thin, crumbly layers like sheets of paper. There were no fossils. This was something called the Toarcian Extinction Event, which marked the end of the Pliensbachian Age. It took place around 183m years ago when an estimated 2 trillion-5 trillion tonnes of carbon were released into the atmosphere and the world warmed up by some five degrees Celsius. The oceans became anoxic (depleted of oxygen), and stagnant. A lot of things died out, which was why there were no fossils in the layers. The presence of so much carbon was responsible for the dark, almost black colour. “It’s one of the events used to compare with modern global warming,” Zalasiewicz said. “We’re beginning to create a modern Toarcian event. We’ve not gone as far yet but we’ve done about half a trillion tonnes of carbon, mostly in one century.”

FOR AN EPOCH to be formalised it must have a starting-point—either a Global Stratigraphic Section and Point (GSSP) or a Global Standard Stratigraphic Age (GSSA). A GSSP is one physical location where the transition between units can be seen. Typically a GSSP is located in a section of rock and marked with a “golden spike” (in actuality a bronze disc). The GSSP for the base of the Silurian Period can be viewed at Dob’s Linn in Moffat, Scotland; the base of the Jurassic at the Kuhjoch section, Tyrol, Austria. Where no GSSP can be identified—for the 4-billion-year-old Eoarchean, say, where there are few physical traces—then a GSSA is used. This gives a chronological point but not a physical reference.