And yet, scientists insist that whether or not the Anthropocene enters history books, the age of humans has begun, as evidenced by the fundamental changes in the conditions on Earth from those of the Holocene.

Epochs are units of geologic time scale that categorise different stages or eras in Earth's history, taking into factors such as Earth's geological, climatic, or biological features. The current Holocene epoch, for instance, is characterised by the development of human civilisation, agriculture, and the rise of modern human societies.

The idea behind marking a new epoch, Anthropocene, was to recognise the sweeping impact humans have had on the planet — its environment, lands and nature.

“These changes have already produced a clear and distinct geological record of such signals as plastics, pesticides, fly ash and the remains of invasive species in recent layers of sand and mud (these being the geological strata of the future); and, many of these planetary changes are effectively irreversible,” Jan Zalasiewicz, emeritus professor of Palaeobiology at the University of Leicester, wrote over email. Jan is the chair of the Subcommission on Quaternary Stratigraphy (SQS), which voted down the proposal to mark the start of the Anthropocene in the mid-20th Century.

This proposal was prepared by 37 scientists in the Anthropocene Working Group (AWG), a body set up in 2009 to research the Anthropocene, who after years of research picked the 1950s when nuclear tests scattered radioactive fallout across the world as the starting point.

A clear starting point needed

But the rules of stratigraphy, the branch of geology concerned with rock layers and how they relate in time, dictate that each interval on the Geologic Time Scale (GTS) needs a clear starting point applicable worldwide.

For instance, the Jurassic period officially began in the Alps, where an ammonite called Psiloceras was found in rocks.

And so the geologists had to answer when the Anthropocene began and whether they needed to update the stratigraphic record — the official timeline of Earth's history from pre-Cambrian to the Holocene. Additionally, they also had to pick a site of the so-called golden spike, or more officially a "Global Boundary Stratotype Section and Point".

When such a point is identified, a gold piece of metal is sometimes hammered into place.

For the Anthropocene, they landed on Crawford Lake in Ontario, Canada, where sediments at the bottom of the lake had near pristine records of geochemical change.

The International Union of Geological Sciences (IUGS) defines every chapter in the planet’s 4.6 billion-year-old history on the basis of when that age or epoch began, what characters define it and where it began.

The Holocene began 11,700 years ago at the end of the last Ice Age.

Acceptance of the vote that the Anthropocene epoch had begun would have meant acknowledging that human actions had brought the Holocene to an end.

Johan Rockstrom, director of the Potsdam Institute for Climate Impact Research, in an address to the World Economic Forum seven years ago explained that the conditions of the Holocene are what made human existence possible, setting in an equilibrium where life could thrive, where the maximum temperature variability is +/-1°C.

Humans, however, have shifted this equilibrium over the last few centuries, with a “great acceleration” setting in the 1950s, scientists say — hence the divide.

The great acceleration argument didn’t make the cut

Geologists, most of whom conducted research together over the last 15 years, lack consensus on whether humanity’s impact so far should be defined as an “epoch”, a period typically lasting hundreds of thousands of years, or an “event”, a far shorter period.

The idea of the Anthropocene was first popularised in the early 2000s when Dutch meteorologist and atmospheric chemist Paul Crutzen wrote: “The Anthropocene could be said to have started in the latter part of the eighteenth century when analyses of air trapped in polar ice showed the beginning of growing global concentrations of carbon dioxide and methane”.

The official work started in 2009, with the setting up of the AWG.

But Crutzen’s proposal, Jan said, was not due to a sudden realisation that humans were altering the functioning and geological record of the planet. “He and his colleagues were perfectly aware that humans had been doing that for millennia. That’s nothing new,” he wrote for The Conversation.

Explaining the rationale for the 1950s starting point, Jan said: “The Anthropocene epoch concept… represents a major, recent change in Earth’s surface chemistry, climate, biology etc from the generally stable conditions that characterised the Holocene. By far the greater part of this major planetary change has taken place in just the last 70 years, as a result of the ‘Great Acceleration’ of population, industrialisation and globalisation that started in the mid-20th century: this is the optimal level, therefore, to represent the beginning of an Anthropocene epoch.”

This argument, however, was found to be too limited by several members of the SQS, and even the AWG which even prompted the resignation of one of the members, Erle Ellis, in 2023.

“To define the Anthropocene as a shallow band of sediment in a single lake is an esoteric academic matter. But dividing Earth’s human transformation into two parts, pre- and post-1950, does real damage by denying the deeper history and the ultimate causes of Earth’s unfolding social-environmental crisis. Are the planetary changes wrought by industrial and colonial nations before 1950 not significant enough to transform the planet?,” Ellis, professor of Geography & Environmental Systems at the University of Maryland, Baltimore County, wrote in his resignation letter to the AWG.

Humans are changing the planet

In an interview after the vote, Ellis said that the purpose of identifying these changes on the geological timescale is to improve understanding of the planet and the changes it goes through.

“The purpose of marking these time breaks in Earth's history is to help understand Earth's geologic changes over huge time intervals based on the limited geological evidence available from the past,” Ellis said. But, “there is no need to do this to understand the geological changes that are unfolding in the present time.”

The SQS was one of the three governing bodies under the IUGS which considered the proposal prepared by the AWG. Sixty percent of each committee had to approve the proposal for it to advance to the next. Instead, the vote was 66% against.

“To be clear: the Anthropocene has never been rejected. The Anthropocene is still as real as it has always been — no one has rejected the realities of the Anthropocene,” Ellis added.

One of the reasons for the rejection of the proposal was the lack of utility such a definition had for scientists, Ellis said.

“The reasons are mostly related to technical aspects… but one of these was the lack of utility for geologists and scientists to mark a break in Earth history so recently when there are already so many tools for marking geologic time that can be used to understand all the details of planetary change,” he said.

But Jan rejected the approach adopted by Ellis and other geologists.

“The Anthropocene as described by Erle Ellis and others is what they call an ‘event’, that encompasses all significant human impacts on Earth reaching back 50 thousand years or more. This is a valid concept — but a wholly different concept to that of Paul Crutzen and the AWG,” he said.

“Giving it the same name, Anthropocene makes little sense. Under a different name, though, it could usefully complement an Anthropocene epoch,” Jan said.

To be sure, an event can be any change in the planet’s history, from a mass extinction to speciation, or even a sudden glacial retreat.

But whatever the side of the debate, scientists agree on one thing: humans are the dominant force of change.

“The Anthropocene represents a clear, sharp reality: a reality that is becoming ever more evident with each passing year,” Jan said.

And now that the vote has been ratified, despite requests from the SQS chair to nullify it, the whole process may have to begin again, perhaps at a later stage.

Tannu Jain, HT's deputy chief content producer, picks a piece of climate news from around the globe and analyses its impact using connected reports, research and expert speak