The End of the Beginning

The 2011 annual report of the International Commission on Stratigraphy’s Subcommission on Quaternary Stratigraphy included the following notification: “The [Anthropocene] Working Group has applied for funding to allow further discussion and networking, and is working to reach a consensus regarding formalisation by, it is hoped, the 2016 IGC [International Geological Congress].” “As if they had so much time and so little money!” sighed Bruno Latour. But then, he admitted, “geologists are used to taking their time.”

The 2016 IGC began in Brisbane on August 29th. The first day’s programme included a paper by Colin Waters, the working group’s secretary, called “The Anthropocene: overview of stratigraphical assessment to date.” The same panel also featured a paper by Stanley Finney, chair of the International Commission on Stratigraphy, on “The mistaken drive to define the ‘Anthropocene’ as an officially recognized unit of the Geologic Time Scale.”

On the same day, the University of Leicester published the results of a series of six votes among 35 members of the working group:

Is the Anthropocene stratigraphically real?  For: 34   Against: 0    Abstain: 1

Should the Anthropocene be formalised?  For: 30   Against: 3    Abstain: 2

Not quite a “consensus.” But, at least among this partly self-selecting group, not far off. No-one disagreed that recent changes in the Earth system have had real effects on the makeup of rock strata that are now in the process of formation. But as the results of the second vote show, it doesn’t necessarily follow that the Anthropocene should be “formalised”—i.e. added to the ICS’s official scale of geological time. Would science be better served by defining the Anthropocene precisely as a stratigraphic unit, or by resting content with the current informal usage? Might formalization be premature?

Hierarchical level of the Anthropocene?  Era: 2    Period: 1.5    Epoch: 20.5    Sub-epoch: 1    Age: 2    Sub-age: 0    None: 1    Uncertain: 3    Abstain: 4

The geological time scale is made up of a hierarchical series of intervals that are nested inside one another like reigns within a dynasty. An Anthropocene era would replace the current Cenozoic era, the 66 million years since the extinction of the terrestrial dinosaurs. An Anthropocene period would replace the 2.6 million year old Quaternary, but remain within the Cenozoic. An Anthropocene epoch, always the most widely discussed option, would terminate the 10,000 year old Holocene, the postglacial epoch of agriculture and cities. An Anthropocene age would subdivide the Holocene.

Base/beginning of the Anthropocene?  ~7ka: 0   ~3ka: 1.3    1610 Orbis: 0    ~1800: 0    ~1950: 28.3    ~1964: 1.3    Diachronous: 4    Uncertain: 0    Abstain: 0

“ka” means “thousands of years ago.” The ~7ka option represents William Ruddiman’s “Early Anthropocene” hypothesis. It’s possible that human influence on global CO2 levels has been detectable ever since then, but if so, back then human influence tended to keep CO2 levels constant, rather than to transform the geological makeup of the planet (as would be required for a new stratigraphic interval). The ~3ka option would reflect things like regional-scale formations of anthropogenic soils, as in this paper.

“1610 Orbis” is a reference to this paper, which proposed dating the Anthropocene to the year of an apparent CO2 minimum that might (or might not) be attributable to reafforestation in the Americas after the Columbian invasion.

The absence of support for a start date around 1800 is a striking outcome. Perhaps it might finally put to bed the fallacy that Anthropocene scientists are all wedded to the idea that significant human impacts on the planet began with the Industrial Revolution, narrowly defined.

The near-consensus on a start date around 1950 reflects the working group’s longstanding emphasis on the “Great Acceleration,” the intense postwar boom in economic-ecological activity. It was then, most members of the group seem to agree, that the planet-wide forces governing the formation of rock strata moved decisively outside the range of Holocene variability. The 1964 option was proposed in the same paper as the 1610 option, and was based on a global peak in radiocarbon (carbon-14) caused by nuclear bomb test fallout. Stratigraphers usually fix their boundaries at the beginnings rather than the peaks of such “excursions,” however.

Voting for a “diachronous” beginning is more or less the same as voting against formalization altogether, because boundaries in the geological time scale are all synchronous, or have “zero time depth.”

GSSA vs GSSP?  GSSP: 25.5    GSSA: 1.5    Uncertain: 8

Intervals defined by a Global Standard Stratigraphic Age are simply said to have begun a certain number of years ago. Intervals defined by a Global Boundary Stratotype Section and Point (a “golden spike”) are defined as beginning at the time when some specific layer of rock or ice somewhere on Earth was formed. (So that if that layer of rock is later found to have been formed 201 million years ago rather than 200 million years ago it means that your geological period is older than you thought, not that the rocks actually date to the previous period.)

That vote represents a significant turnaround from this paper, in which many working group members signed on to a proposal to define the Anthropocene by a GSSA. Sceptics pointed out in reply that current standard practice is to base as many intervals as possible on the tangible foundations of a GSSP. It seems that now the Anthropocene is heading that way too.

What is the Primary Signal?  aluminium: 0    plastic: 3    fuel ash particles: 2   carbon dioxide concentration: 3    methane concentration: 0    carbon isotope change: 2    oxygen isotope change: 0    radiocarbon bomb spike: 4    Plutonium fallout: 10    Nitrate concentration/nitrogen isotope change: 0    Biostratigraphic: extinction/assemblage change: 0    Other (lead, persistent organic pollutants, technofossils): 3    Uncertain: 2   Abstain: 6

If you want to have a golden spike, you need to have something to look for in the geological record. The top two candidates, radiocarbon and plutonium anomalies, are both the result of nuclear test fallout. It’s notable that fuel ash only picked up two votes: that had seemed the strongest alternative candidate. Carbon dioxide concentration was the measure proposed in Paul Crutzen’s earliest papers on the Anthropocene. I’m stuck by the absence of support for a biostratigraphic approach.

This vote tends to suggest that the base of the Anthropocene epoch could yet end up being dated to 1952, and being associated with the beginning of planet-wide radionuclide fallout caused by thermonuclear weapons tests. The first H-bomb test shot, Ivy Mike, is pictured at the top of this page. I wrote about the events of the day Mike was detonated here.

For a few hours last Monday, the formal administration of stratigraphic time divisions was the headline story on the Guardian website.

But the working group’s vote doesn’t make the Anthropocene epoch official. Not by a long way. The next step is to identify an actual physical talisman in which the “golden spike” might be fixed. Jan Zalasiewicz, convenor of the working group, was quoted in Science: “we’ll go and get our hands dirty, beginning to look for sections that we can formally propose.”

With a section in hand, a detailed formal proposal for the new epoch must be prepared (here’s the equivalent for the Holocene epoch). That proposal must be approved by a 60% supermajority of the ICS Subcommission on Quaternary Stratigraphy, then by a supermajority of the ICS executives and chairs of subcommissions, then finally by a majority of the Executive Committee of the International Union of Geological Sciences. Only after that could the time charts be redrawn.

“If we were very lucky and someone came forward with, say, a core from a classic example of laminated sediments in a deep marine environment, I think three years is possibly viable,” Zalasiewicz said. Conversely:

Should ICS decide against the Anthropocene, some stratigraphers fear, they could be swamped with bad press. “I feel like a lighthouse with a huge tsunami wave coming at it,” [Stanley] Finney says. Phil Gibbard, a stratigrapher at the University of Cambridge in the United Kingdom and a working group member who voted against the proposal, also worries about a backlash. “We’re nervous,” he says.

The next International Geological Congress will take place in Delhi in March 2020.

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