Scientists Reject Proposal to Define the Anthropocene, a Geological Age Marked by Human Activity

A group of scientists has voted against defining a new geological period called the Anthropocene, marked by humans’ impact on the planet, the New York Times’ Raymond Zhong reports.

In October, the Anthropocene Working Group proposed that an Anthropocene epoch started in the mid-20th century, when nuclear weapons tests left radioactive fallout across the planet. They submitted this proposal to the Subcommission on Quaternary Stratigraphy (SQS), which establishes a standard timescale for the past 2.6 million years and is part of the International Union of Geological Sciences.

Twelve SQS members rejected the proposal, while four voted in favor and two abstained, according to the New York Times. This decision came as a surprise to many scientists, per New Scientist’s Chen Ly.

“We’ve provided ample evidence that the rate at which humans have an impact on the planet has increased dramatically,” working group member Francine McCarthy, a paleontologist at Brock University in Canada, tells the Washington Post’s Sarah Kaplan. “It’s hard to understand how anyone who looks at the science can say that there wasn’t a massive tipping point in the mid-20th century.”

One reason the proposal was rejected is that human impacts on the planet started before the mid-20th century, Mike Walker, an SQS voting member who studies climate change at the University of Wales, tells New Scientist. As a result, some experts thought the proposed definition of the epoch was too limited.

“It constrains, it confines, it narrows down the whole importance of the Anthropocene,” Jan A. Piotrowski, an SQS voter and geologist at Aarhus University in Denmark, tells the New York Times. “What was going on during the onset of agriculture? How about the Industrial Revolution? How about the colonizing of the Americas, of Australia?”

The current period of geologic time is the Holocene epoch, which began 11,700 years ago. Its start coincides with the end of the last ice age, and it has been a relatively warm period.

Homo sapiens evolved hundreds of thousands of years ago and have significantly reshaped the planet by cutting down forests, detonating nuclear weapons, dumping plastics on land and in the oceans, driving the extinction of many species and burning fossil fuels, releasing greenhouse gases into the atmosphere.

The term “Anthropocene” was devised in 2000 to describe the present geological time period shaped by humans’ impact on the planet. “Anthropo,” from Greek, means “human.”

Fifteen years ago, the working group started searching for a geological site that would best represent humanity’s impact on Earth and provide evidence for the Anthropocene, per CNN’s Katie Hunt. Last year, they settled on Crawford Lake in Ontario, Canada. The lake’s sediment has preserved a record of human activity, including microplastics, evidence of burning fossil fuels and a measure of radioactive plutonium from testing nuclear weapons.

“All these lines of evidence indicate that the Anthropocene, though currently brief, is—we emphasize—of sufficient scale and importance to be represented on the geological time scale,” working group members Simon Turner, a geographer and University College London, and Colin Waters, a geologist at the University of Leicester in England, write to New Scientist in an email.

The working group decided to propose that the Anthropocene started in 1952, when radioactive fallout from hydrogen bomb tests was first measured, Erle C. Ellis, an ecologist at the University of Maryland, Baltimore County, writes in the Conversation. Ellis used to be a member of the working group but resigned because he thought the group was defining the Anthropocene too narrowly.

“By tying the start of the human age to such a recent and devastating event—nuclear fallout—this proposal risked sowing confusion about the deep history of how humans are transforming the Earth, from climate change and biodiversity losses to pollution by plastics and tropical deforestation,” Ellis writes in the Conversation.

Ultimately, the SQS rejected the working group’s proposal. “It suggests that all of a sudden, within my lifetime, the changes that are affecting the planet suddenly appeared,” Philip Gibbard, a geologist at the University of Cambridge in England who voted against the proposal, tells the Washington Post. “But humans have in fact been influencing the natural environment for 40,000 years.”

For its part, the working group has many members “who wish to carry on as a group, in an informal capacity, that will continue to argue the case that the evidence for the Anthropocene as an epoch should be formalized,” Waters writes to CNN in an email.

Importantly, the decision is not a rejection of the idea that humans have had a profound impact on the Earth.

“This has nothing to do with the evidence that people are changing the planet,” Ellis tells the New York Times. “The evidence just keeps growing.”

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Will Sullivan is a science writer based in Washington, D.C. His work has appeared in Inside Science and NOVA Next.