After two years, researchers are resurfacing a voting controversy over whether Earth is officially in a geological epoch called the Anthropocene.

In 2024, the International Union of Geological Sciences (IUGS) upheld a decision to reject a proposal to establish our current era, when humans are altering the planet, as a new epoch in the rock record. Now, some scholars say that there are unpublished documents showing that the proposal’s rejection was illegitimate, and that the rationale for the decision was never adequately explained.

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“It was such a historical decision,” says Jürgen Renn, a historian of science at the Max Planck Institute of Geoanthropology in Jena, Germany. “It should be clear to the world — it should be transparent,” says Renn, who co-authored a paper, out today in the journal Earth’s Future¹, laying out the accusations.

Renn and his co-authors call for the IUGS to publicly release key documents related to the vote. They also call for an independent review of the process to maintain “public trust in our capacity to understand and respond to planetary transformation”.

But researchers involved in the vote maintain that the process was fair. Adele Bertini, a geologist at the University of Florence in Italy, who co-chaired the voting subcommittee, says she is open to scrutiny of the documents if it would help support the legacy left by all the “remarkable science” that went into creating the proposal. She also points out that she co-authored a comment in the journal Nature Reviews Earth & Environment last month giving a technical explanation for the proposal’s rejection².

Bitter debate

The allegations from Renn and his co-authors are the latest salvo in a bitter debate among geologists about whether the Anthropocene should be formally recognized in the stratigraphic record. Currently, the planet is in the Holocene epoch, which started 11,700 years ago with the end of the last glacial period. In 2009, a team of researchers called the Anthropocene Working Group began gathering evidence to support the idea that industrialization by humans has initiated a new epoch.

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This effort culminated in a proposal to establish the Anthropocene as having started in 1952, when a layer of plutonium from nuclear weapons testing appeared in Earth’s strata. This physical marker correlated with other big human-driven shifts on Earth, including a spike in the concentration of carbon dioxide and methane in the atmosphere. Another paper published last month in Nature Reviews Earth & Environment details the evidence collected to support this view³.

The case for the Anthropocene remains strong,” says Jan Zalasiewicz, a geologist at the University of Leicester, UK, who led much of the working group’s efforts and who co-authored that review. The Anthropocene is already a widely used term in many fields of research, but scientists who support the Anthropocene proposal argue that a formal definition is needed to give it stability and legitimacy in geoscience.

When the proposal was put to the vote in 2024, before a subcommittee of stratigraphers, it was rejected, 12 to 4, with two members abstaining. “I was born in 1949, and I don’t remember seeing any geological boundaries during that period,” says Phil Gibbard, a geologist at the University of Cambridge, UK, who voted to reject the proposal. He and others have since argued for a more flexible definition, referring to the Anthropocene as an ‘event’ rather than an epoch. (Geological events include significant episodes of planetary change, such as the Great Oxidation Event, when Earth’s atmosphere first filled with high concentrations of oxygen.)

Geoethical questions