The Golden Spike and the Age of Us

The field in brief

Chronostratigraphy studies time as it is written in rock. Its product is the Geologic Time Scale, the nested ladder of eons, eras, periods, epochs and ages that carves some 4.6 billion years into named blocks.[6] We live in the Holocene, the epoch that began about 11,700 years ago as the last ice age loosened its grip.[3] The Anthropocene was proposed as the unit that would end the Holocene and open an age of human dominance.[2]

The field's central instrument is the GSSP, known informally as the "golden spike."[6] A GSSP is a single agreed point in one real rock or sediment section, at one place on Earth, that physically fixes the lower boundary of a time-unit.[6] A unit becomes official when a marker in the layers, such as a fossil's first appearance or a chemical spike, is chosen and then ratified by committee.[5] The rock, not the calendar, holds the definition.

Two more terms carry the fight. Varves are annual layers of lake or sea-floor sediment, laid down like tree rings, each year's deposit distinct from the next.[9] An "event," in stratigraphy, is an informal happening that leaves traces at different times in different places, unlike an epoch, which demands one fixed global boundary.[4] That distinction, epoch versus event, is the axis the whole dispute turns on.[4]

The fight

The word arrived in 2000, coined by the atmospheric chemist Paul Crutzen to name an age shaped by people. In 2009 the Subcommission on Quaternary Stratigraphy created an Anthropocene Working Group to test whether the idea could be made official, a group later chaired by Colin Waters and Jan Zalasiewicz of the University of Leicester.[6] In 2019 the group voted, bindingly, to seek a boundary in the mid-twentieth century, at the "Great Acceleration" of population, industry and fallout.[6] Its chosen marker would be radioactive plutonium from nuclear tests, scattered worldwide within a few years.[2]

Not everyone in geology accepted the premise. In 2022 a group led by Philip Gibbard of Cambridge, with the ecologist Erle Ellis and the IUGS secretary-general Stanley Finney among its authors, argued that the Anthropocene was better treated as a geological "event," not an epoch.[4] Human impact, they wrote, began at different times in different places, and an event framing captured that spread far better than a single 1950 line.[4] In 2023 Ellis resigned from the Working Group, saying it had grown intolerant of dissent and that dating human transformation from 1950 was bad for public understanding.[7]

The Working Group pressed on. In July 2023 it named its golden-spike site: Crawford Lake in Ontario, a meromictic lake whose deep water never mixes, preserving undisturbed annual varves.[9] Francine McCarthy of Brock University had championed the lake for decades, and its mud holds a clean plutonium spike from 1952, alongside fly ash and nitrogen from fertilizer.[5][9] The proposal set the Anthropocene's base at roughly 1950.[5]

The decision fell to the Subcommission's voting members in early 2024. On 4 March the count was announced: four in favour, twelve against, three abstentions, a decisive rejection.[1][2] Then the losing side revolted. Zalasiewicz and Martin Head of Brock University declared the vote invalid, alleging that officers running it had overstayed their terms, that discussion had been cut short, and that conflicts of interest tainted the count.[8][2]

The historian of science Naomi Oreskes of Harvard backed them, saying the irregularities suggested the decision was not made on scientific grounds.[8] The parent bodies disagreed. On 20 March 2024 the International Union of Geological Sciences affirmed that the vote's conductors, Liping Zhou of Peking University and Adele Bertini of Florence, had acted fully within the rules, and that the rejection stood.[1] The Holocene, officially, continues.[1]

What the fight reveals

The dispute exposes where a rock science actually keeps its authority: not only in strata but in committees, quorums and terms of office.[1][8] The evidence at Crawford Lake is unusually strong on its own terms, since the bomb-fallout layer is one of the most globally synchronous markers ever laid down, exactly the sharp, worldwide signal a golden spike wants.[5][2] On the physical case for a clean 1950 boundary, the Working Group held the better hand.[5]

Yet the field's conventions cut the other way. Epochs usually span hundreds of thousands of years, and a unit barely seventy years old and still accumulating unsettled many voters trained on deep time.[8] The "event" framing has gained ground since, precisely because it frees the idea from any single ratified line.[10][4]

What stays unresolved is not whether humans have marked the rock. No one in the dispute denies that a permanent, global, human-made layer now exists.[10] The open question is its rank and its name, and whether the March vote was settled by science or by procedure, a question the two camps still answer in opposite ways.[1][8]