In the annals of geology, the Anthropocene saga may become known as the Battle of the Stratigraphers.
One side in this skirmish is made up of traditional geoscientists, almost all academics, many of them leading experts in the Quaternary. The other includes scientists from multiple disciplines, determined to send out a warning about the dangers of human impact on the global environment.
The first side believes the conflict has ended, conclusively.
For the other side, the battle rages on.
History of an Epoch
In 2000, scientists Paul Crutzen and Eugene Stoermer proposed the Anthropocene as a new geological epoch. Crutzen, a Dutch atmospheric chemist, and Stoermer, a professor of biology at the University of Michigan (both have since passed away), listed several examples of human impact on the natural environment, writing in the newsletter of the International Geosphere-Biosphere Programme.
“Considering these and many other major and still growing impacts of human activities on earth and atmosphere, and at all, including global, scales, it seems to us more than appropriate to emphasize the central role of mankind in geology and ecology by proposing to use the term ‘anthropocene’ for the current geological epoch,” they wrote, setting the battle line for future events.
Philip Gibbard, emeritus professor of Quaternary palaeoenvironments at the University of Cambridge in England, would play a significant role in this saga. At one point he attended a meeting of the Anthropocene Working Group in Maintz, Germany.
Members of the group proposed that the beginning of the Anthropocene – the beginning of significant human impact on the global environment – should be set in the middle of the 20th century, around the time of the first thermonuclear bomb tests.
“I was sitting in the audience and I was thinking, ‘This is not right. This is not right at all,’” Gibbard recalled.
It was a harbinger of trouble for the proposed Anthropocene epoch.
End of an Epoch
An official declaration came in March: Geologically, the world remains in the Holocene epoch. Instead of a new epoch following the Holocene, the Anthropocene will become known as an “event” – an ongoing period of noticeable and notable human influence on nature.
Decisions about additions to the Geological Time Scale come under the jurisdiction of the International Union of Geological Sciences. Voting on the status of the Anthropocene fell to the 22-member IUGS Subcommission on Quaternary Stratigraphy.
By a tally of 12 to four, with three abstaining and three not voting, it decided that the Anthropocene should not be added to the time scale as a new epoch. That verdict immediately sparked controversy, and a sharply negative response from members of the AWG, which had proposed the addition.
When Did It Start?
To Gibbard, the decision made complete sense. So did casting the Anthropocene as an ongoing geological event, considering the long history of human activity.
“We know that humans have impacted the world’s environment since at least the middle of the last glacial period, which would put us back 40,000 years, or even more,” Gibbard said.
“We know that the impact of civilization in China started over 5,000 years ago,” he noted.
Even Crutzen’s first proposals of an Anthropocene epoch started the clock ticking during the Industrial Revolution, in the 18th century. Put bluntly, traditionalists weren’t about to pull the trigger on this deal with a beginning date in 1950.
“One of the foremost reasons that my colleagues and I rejected a starting point set in the middle of the 20th century, was that it does not recognize the impacts of humans that began many thousands of years earlier in parts of the world,” Gibbard explained.
A ‘Wholly Different Concept’
Jan Zalasiewicz, an emeritus professor at the University of Leicester, also has a key role in the saga. Zalasiewicz served as chair of the SQS and a member of the AWG. To him, the Anthropocene decision seemed short-sighted, and flat-out wrong.
“A notable feature of the rejection of the Anthropocene is that it is largely based on a priori beliefs or convictions, which largely ignores the detailed stratigraphic evidence amassed in the Anthropocene Working Group’s proposal,” Zalasiewicz stated.
As a member of both the Subcommission and the Working Group, Zalasiewicz declined to vote on the Anthropocene epoch issue. He considers the Anthropocene-as-event “a wholly different concept.”
“The (proposed Anthropocene) event encompasses all detectable anthropogenic impacts stretching back through all of the Holocene and far into the Pleistocene, for 50,000 years or more,” he noted.
“The Anthropocene as epoch means something very different: a marked shift in planetary conditions from the long stability of the Holocene, which is most clearly marked in the mid-20th century, which has already left a clearly identifiable and precisely correlatable stratigraphic record, and which is effectively irreversible,” he explained.
The Criterion
Although a huge amount of data about the Anthropocene was gathered and considered by the IUGS, precise measurements and defining norms did not determine the ultimate decision. The Anthropocene did not somehow fail to meet a set of exacting standards or requirements for a distinct epoch.
In the end, no rating scale said the Anthropocene had insufficient epoch-ness, or wasn’t epoch-y enough. The Subcommission’s verdict was not a matter of applying specific scientific limits – it was a judgment call.
“The decision was based on our knowledge of human interactions with natural systems throughout the Late Pleistocene – and in particular in the Holocene interglacial, in which we live, humans having modified the physical and biotal environment throughout the period,” Gibbard explained.
“The changes in the last few decades (up to the) present are in essence the result of this continuing, ongoing and intensifying activity,” he said.
Helen Bostock, associate professor in the School of Earth and Environmental Sciences at the University of Queensland in Brisbane, Australia, is a voting member of the Subcommission on Quaternary Stratigraphy.
She voted in favor of the Anthropocene as a new epoch.
“I am actually a bit surprised by the decision to reject the Anthropocene proposal,” she related.
“As an oceanographer and palaeoceanographer I see very clear evidence that humans have altered the climate system and we see very clear anthropogenic signals in marine sediments due to human activities such as land clearing, plastic pollution, radioactive signals, heavy metals, etc. These clearly all increase around 1950s to 1960s,” she noted.
To her, the debate among members of the Subcommission “appears to be between whether the Anthropocene should be an epoch or an event.” She also noted the debate in the broader scientific community about a credible starting date for when the Anthropocene began.
“The term ‘Anthropocene’ has been used in many different disciplines, with a wide range of informal definitions. The hope of defining a new geological time-period as the Anthropocene would help to formalize the definition,” Bostock explained.
“But given that it has been used in the literature for the past 20 years – perhaps this definition would be too narrow. My hope is that this could be the opportunity to open the debate up to a broader community and discussion, beyond the geoscientists,” she added.
Gibbard today serves as secretary-general of the International Commission on Stratigraphy, the largest and oldest constituent scientific body of the IUGS. Previously he was chair of the SQS, where he was succeeded by Zalasiewicz.
About 15 years ago, “we were thinking we should consider whether this idea of the Anthropocene as proposed by Crutzen and Stoermer had any validity in geology,” Gibbard said.
“I invited Jan Zalasiewicz to form a working group to determine whether we could consider the geological implications of the Anthropocene concept. He formed a working group and got together quite a large group of people. It started as a rather small group, but broadened out,” he explained.
Gibbard said the Anthropocene Working Group, formed in 2009, ended up including experts from multiple disciplines, “which is good, because we were talking about things that happened in recent times.”
Years passed before the AWG settled its views on the Anthropocene question, but in 2019 it cemented a formal position. By an overwhelming majority vote, it proposed that the Anthropocene should be recognized as a formal chrono-stratigraphic unit, with its base being one of the stratigraphic signals around the mid-20th century.
AWG leadership then asked for time to finalize the site selected for a reference Global Boundary Stratotype Section and Point (GSSP, also known as a “golden spike”), an agreed-upon and required stratigraphic reference point that defines the lower boundary of a stage on the GTS.
The group chose evidence captured in the sediments of Crawford Lake in Ontario, Canada, starting the Anthropocene around 1950, based on the presence of artificial radionuclides from nuclear bomb tests and evidence of the “Great Acceleration” of world population growth, industrialization and globalization. Because of the lake’s depth and stability, those sediments preserve a clear stratigraphic record.
By last October, the AWG was ready to submit its report and final recommendation to the SQS. After a period set aside for discussion and voting, results were announced on March 4: no epoch for the Anthropocene.
Defining the Division, Divisive Definitions
Supporters of the proposal, including members of the working group, felt that relegating the Anthropocene to an event would minimize its significance.
“The ‘Anthropocene event’ is a valid concept, but it is not an event in the standard sense of event stratigraphy … nor is it anything like the Anthropocene as originally conceptualized or proposed by the AWG,” Zalasiewicz responded.
“It is problematic also in that, as published, the event obscures or hides the very large changes of the last 70 years and so may give the impression that these large, recent changes – e.g. in atmospheric greenhouse gas levels – are of little importance.,” he added.
The traditionalist stratigraphers saw it as exactly the opposite. Limiting the scope of human impact to a few decades would minimize its true importance, they believed, and they compared the Anthropocene event to the great events of Earth history, including the Great Oxygenation, the Cambrian Explosion and the Great Ordovician Biodiversification events.
“I think the event concept has been very warmly welcomed. I find it a much more practical, sensible solution,” Gibbard said.
“By using the word ‘event’ we are not only catering for the geological community, we are catering for use across the disciplines,” he added, noting, “the beauty of the word is that is can describe anything from a raindrop falling into a puddle to things that happen over a long period of time.”
After the decision was announced, Zalasiewicz criticized the handling of the consideration process as well as the legitimacy of the vote itself, noting “the voting process at this level was deeply problematic.”
“Among those 16 members (of the Subcommission) who took part in voting, 11 cast their votes while being ineligible to vote, since the term of office for each of them had clearly exceeded 12 years – the limit allowable by ICS Statutes to retain voting rights,” he claimed.
This prolonged saga that started as a technical discussion over a moment in geological time somehow ended up by pitting stratigraphers against each other, in what has been called an Epoch Fail.
“It’s been very divisive,” Gibbard said. “It’s been difficult.”