In March 2024, geologists formally closed a fifteen-year debate: the Anthropocene will not be added to the Geologic Time Scale as a new epoch. The Subcommission on Quaternary Stratigraphy (SQS), part of the International Commission on Stratigraphy (ICS), voted to reject the proposal, and the International Union of Geological Sciences (IUGS) approved that decision on March 26, 2024. The term itself remains widely used—but as an informal description of human-driven planetary change, not as a formal unit of geological time.
What Is the Anthropocene? Defining Humanity's Geological Impact
The Anthropocene is a proposed term for a period in which human activity—industrialization, resource extraction, habitat destruction, and the chemical transformation of atmosphere and oceans—leaves a detectable mark on Earth's strata. The Natural History Museum in London describes the underlying question as stratigraphic: whether our impact will be visible in the fossil record millions of years from now, and whether a single marker could separate this period from the Holocene, the epoch that began roughly 11,700 years ago.
That framing matters, because the debate was never about whether humans are reshaping the planet. It was about whether that reshaping fits the strict rules geologists use to divide deep time. Informally, "Anthropocene" already appears across the sciences and humanities as shorthand for an age of human dominance. The question before the ICS was whether it deserved a formal place on the International Chronostratigraphic Chart.
The Formal Process of Geological Time Classification
Formal geological time units are not declared by consensus; they are ratified. The ICS oversees the International Chronostratigraphic Chart, and any new epoch requires a proposal demonstrating both a stratigraphic basis and utility for geoscientists. The Anthropocene Working Group (AWG) of the SQS spent years preparing exactly such a proposal, seeking to establish the Anthropocene as a new chronostratigraphic series and corresponding epoch within the Geologic Time Scale.
The central requirement is a "golden spike"—formally a Global Boundary Stratotype Section and Point—a physical reference in rock layers that marks the boundary between two time units. As the Natural History Museum explains, such a marker must be significant enough to remain detectable in strata thousands or millions of years into the future. This demand for a single, globally synchronous signal became the crux of the entire dispute.
The Rejected Anthropocene Epoch Proposal: March 2024 Decision
The AWG's proposal centered on a specific location and date. As described by the Anthroecology Lab, the proposal would have defined the Anthropocene as a band of sediment in Crawford Lake, Ontario, sitting above a spike in plutonium isotopes from nuclear bomb tests dated to 1952. Crawford Lake's annually layered sediments preserve a clear, datable record of mid-twentieth-century human signatures.
That proposal went to the SQS voting membership, which rejected it. The joint statement by the IUGS and the ICS, issued with the delegated authority of the IUGS President and Secretary General, records that the vote by the SQS "to reject the proposal for an Anthropocene Epoch as a formal unit of the Geologic Time Scale is approved," dated March 26, 2024. The AWG is now listed as a former working group of the SQS.
Arguments Against Formal Epoch Status
The rejection reflected long-standing stratigraphic objections. Writing in GSA Today in 2016, Stanley Finney and Lucy Edwards of the ICS community questioned whether a single boundary could capture human impact, and framed the formalization push as potentially more of a political statement than a scientific decision. Their concern was procedural: epochs are defined by boundaries in rock, not by the importance of the changes they record.
A separate critique, developed by Mark Maslin and colleagues at University College London, targets the mid-twentieth-century start date itself. Human transformation of Earth, they argue, has been diachronous—unfolding at different times in different places—and heterogeneous, from early agriculture through industrialization to the post-war "Great Acceleration." A single 1952 plutonium spike, however real, cannot represent a process that began millennia earlier in some regions. A formal epoch, they contend, would rigidly constrain a concept that describes an uneven, ongoing transformation.
The Anthropocene as a Geological 'Event': An Alternative View
The UCL group's alternative is to define the Anthropocene as a time-transgressive geological "event": the aggregated effects of human activities transforming the Earth system and altering biodiversity, producing a substantial record in sedimentary strata and human-modified ground. Geological events—unlike epochs—do not require a single global start date or ratification by stratigraphic bodies.
This framing, they argue, eliminates ambiguity in how the term is used and frees it from alignment with established Holocene time units. It can be grounded in the widespread stratigraphic evidence of human-modified deposits while acknowledging that the transformation has been a socially differentiated process. The Anthroecology Lab makes the same point in plainer language: the Anthropocene remains useful when defined as an ongoing, intensifying planetary geological event, analogous to the Great Oxidation Event.
Epoch vs. Event: A Comparison of Classification Frameworks
The two proposals answer different questions. The epoch proposal asked whether human impact warrants a new formal division of geological time; the event proposal asks only how best to describe that impact. The table below compares them across the four dimensions that drove the SQS vote.
| Dimension | Formal Epoch Proposal (Rejected) | Geological "Event" Alternative |
|---|---|---|
| Definition | A new chronostratigraphic unit within the Geologic Time Scale, marked by a specific global stratigraphic signal. | A time-transgressive, ongoing period of human-induced change to Earth systems, without rigid boundaries. |
| Formal Status | Required ratification by the ICS and IUGS; the SQS, a body under the ICS, rejected it in March 2024. | Informal; requires no ratification by stratigraphic bodies to be scientifically recognized or discussed. |
| Start Date | A fixed date—mid-20th century, exemplified by the 1952 plutonium spike—anchored by a "golden spike" at a specific site. | No single fixed start; onset varies regionally and temporally with the human impacts considered. |
| Implications for the Time Scale | Would have added a new, distinct unit to the official Geologic Time Scale, altering the formal geological record. | Recognizes human impact without changing the formal structure of the Geologic Time Scale. |
Read together, the rows show why the vote went as it did: the epoch proposal's defining strength—a precise, globally synchronous boundary—was precisely what critics found unrepresentative of a sprawling, uneven process. The event framework keeps the descriptive power while discarding the requirement that failed.
Understanding the Anthropocene's Future Classification
Readers should recognize that the formal rejection of the Anthropocene as an epoch does not negate the scientific consensus on human-driven planetary change, but rather refines how that impact is categorized within geology. The Crawford Lake plutonium signal, the stratigraphic evidence of human-modified deposits, and the broader record of transformation all stand; what changed in March 2024 is the label's formal standing. The measurable indicator to watch is continued academic discussion and publications regarding the Anthropocene as a geological "event" or other informal classifications—if that literature grows, the event framework will have become the working consensus; if a revised formal proposal resurfaces through the SQS and ICS, the epoch question will have reopened on new stratigraphic grounds.
