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After 15 years of discussion and exploration, a committee of researchers has decided that the Anthropocene — generally understood to be the age of irreversible human impacts on the planet — will not become an official epoch in Earth’s geologic timeline. The ruling, first reported by the New York Times, is meant to be final, but is being challenged by the chair and a vice-chair of the committee that ran the vote.

Twelve members of the international Subcommission on Quaternary Stratigraphy (SQS) voted against the proposal to create an Anthropocene epoch, while only four voted for it. That would normally constitute an unqualified defeat, but a dramatic challenge has arisen from the chair of the SQS, palaeontologist Jan Zalasiewicz of the University of Leicester, UK, and one of the group’s vice-chairs, stratigrapher Martin Head of Brock University in St Catharines, Canada.

In a 6 March press statement, they said that they are asking for the vote to be annulled. They added that “the alleged voting has been performed in contravention of the statutes of the International Commission on Stratigraphy”, including statutes governing the eligibility to vote. Zalasiewicz told Nature that he couldn’t add more just yet, but that neither he nor Head “instigated the vote or agreed to it, so we are not responsible for procedural irregularities”.

The SQS is a subcommittee of the International Commission on Stratigraphy (ICS). Normally, there would be no appeals process for a losing vote. David Harper, a geologist at Durham University, UK, who chairs the ICS, had earlier confirmed to Nature that the proposal “cannot be progressed further”.

Proponents could put forward a similar idea and start all over after a cooling-off period of 10 years.

The proposal would have ended the current Holocene epoch, which has been going on since the end of the last ice age 11,700 years ago, and started the Anthropocene in the year 1952. This is when plutonium from hydrogen-bomb tests showed up in the sediment of Crawford Lake near Toronto, a site chosen by some geologists as capturing a pristine record of humans’ impact on Earth. Other signs of human influence include microplastics, pesticides and ash from fossil-fuel combustion.

But pending the resolution of the challenge, the lake and its plutonium residue won’t get a ‘golden spike’ designation from geologists now. Selecting one site as such a marker “always felt a bit doomed, because human impacts on the planet are global”, says Zoe Todd, an anthropologist at Simon Fraser University in Burnaby, Canada. “This is actually an invitation for us to completely rethink how we define what the world is experiencing.”

A cultural concept

Although the Anthropocene probably will not not be added to the geologic timescale, it remains a broad cultural concept already used by many to describe the era of accelerating human impacts, such as climate change and biodiversity loss. “We are now on a fundamentally unpredictable planet in ways that we have not experienced for the last 12,000 years,” says Julia Adeney Thomas, a historian at the University of Notre Dame, in Indiana. “That understanding of the Anthropocene is crystal-clear.”

The decision to reject the designation became public through the New York Times on 5 March, after the SQS had concluded its month-long voting process, but before committee leaders had finalized discussions and made an official announcement. Philip Gibbard, a geologist at the University of Cambridge, UK, who is on the SQS, says that the crux of the annulment challenge is that Zalasiewicz and Head objected to the voting process kicking off on 1 February. The rest of the committee wanted to move forward with a vote and did so according to SQS rules, Gibbard says. “There’s a lot of sour grapes going on here,” he adds.

Had the proposal made it through the SQS, it would have needed to clear two more hurdles: first a ratification vote by the full stratigraphic commission, and then a final one in August at a forum of the International Union of Geological Sciences.

Frustrated by defeat

Some of those who helped to draw up the proposal, through an ‘Anthropocene working group’ commissioned by the SQS, are frustrated by the apparent defeat. They had spent years studying a number of sites around the world that could potentially represent the start of a new human-influenced epoch. They performed fresh environmental analyses on many of the sites, including studying nuclear debris, fly ash, and other markers of humans’ impact in their geological layers, before settling on Crawford Lake.

“We have made it very clear that the planet we’re living on is different than it used to be, and that the big tipping point was in the mid-twentieth century,” says Francine McCarthy, a micropalaeontologist at Brock University who led the Crawford Lake proposal1. Even though the SQS has rejected it, she says she will keep working to highlight the lake’s exceptionally preserved record of human activities. “Crawford Lake is just as great a place as it ever was.”

“To be honest, I am very disappointed with the SQS outcome,” says Yongming Han, another working group member and a geochemist at the Institute of Earth Environment of the Chinese Academy of Sciences in Xi’an. “We all know that the planet has entered a period in which humans act as a key force and have left indisputable stratigraphic evidences.”

For now, the SQS and the ICS will sort out how to handle Zalasiewicz’s and Head’s request for a vote annulment. Meanwhile, scientific and public discussions about how best to describe the Anthropocene continue.

One emerging argument is to define the Anthropocene as an ‘event’ in geological history — similar to the rise of atmospheric oxygen just over 2 billion years ago, known as the Great Oxidation Event — but not as a formal epoch2. This would make more sense because geological events unfold as transformations over time — such as humans industrializing and polluting the planet — rather than an abrupt shift from one state to another, says Erle Ellis, an ecologist at the University of Maryland Baltimore County in Baltimore, Maryland. “We need to think about this as a broader process, not as a distinct break in time,” says Ellis, who resigned from the Anthropocene working group last year because he felt it was looking at the question too narrowly.

This line of thinking played a role in at least some of the votes to reject the idea of an Anthropocene epoch. Two SQS members told Nature they voted down the proposal in part because of the long and evolving history of human impacts on Earth.

“By voting ‘no’, they [the SQS] actually have made a stronger statement,” Ellis says, “that it’s more useful to consider a broader view — a deeper view of the Anthropocene.”

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