An influential panel of scientists voted this week to designate a new geologic epoch—the Anthropocene—to mark the profound ways that humans have altered the planet. That decision, by the 34-member Anthropocene Working Group (AWG), marks an important step toward formally defining a new slice of the geologic record, which has generated intense debate within the scientific community over the past few years.

The panel plans to submit a formal proposal for the new epoch by 2021 to the International Commission on Stratigraphy, which oversees the official geological time chart.

Twenty-nine members of the Anthropocene Working Group (AWG) supported the Anthropocene designation and they also voted in favour of starting the new epoch in the mid-20th century, when a rapidly rising human population accelerated the pace of industrial production, use of agricultural chemicals and other human activities. At the same time, the first atomic bomb blasts littered the globe with radioactive debris that became embedded in sediments and glacial ice, becoming part of the geologic record.

“The Anthropocene works as a geological unit of time, process and strata,” says Jan Zalasiewicz, chair of the AWG, who wasn’t confident of that conclusion when the AWG first began its work a decade ago. But the vote demonstrates that the group has mostly coalesced around the geological unit. “It is distinguishable. It is distinctive,” he says.

The results of the vote were not surprising, given that they solidified an informal vote that was taken in 2016 at the International Geological Congress in Cape Town, but the decision invigorates the race to find a geologic marker signalling the end of the Holocene epoch and the start of one shaped by human activity.

The AWG was established by the Subcommission on Quaternary Stratigraphy, which in turn is part of the International Commission on Stratigraphy. Having decided to go ahead with the new epoch, the group will now focus on identifying a definitive geologic marker or “golden spike”, which is technically called a Global boundary Stratotype Section and Point (GSSP).

The group is considering ten candidate sites from around the globe, from a cave in northern Italy to corals in the Great Barrier Reef to a lake in China. Next week, many of the scientists involved will gather in Berlin to coordinate the next two years of research. They hope to identify a single site to include in their formal proposal. They must also define the type of physical evidence in the sedimentary record that represents the start of the epoch. The group is considering whether to choose the radionuclides that came from atomic bomb detonations from 1945 until the Limited Nuclear Test Ban Treaty of 1963, says Zalasiewicz.

Once the AWG makes its formal proposal, it would be considered by several more layers of the International Commission on Stratigraphy. And if it makes it past that group, final ratification would come from the executive committee of the International Union of Geological Sciences.

Four members of the AWG voted against the idea of designating the Anthropocene as a new epoch. They objected to the group’s efforts to find a single clear signal that can be found globally in the geological record, as opposed to acknowledging the progressive impacts of humans on the world, starting with agriculture in prehistoric times. “The stratigraphic evidence overwhelmingly indicates a time-transgressive Anthropocene with multiple beginnings rather than a single moment of origin,” says Matt Edgeworth, an archaeologist at the University of Leicester and a member of the AWG. Naming a new epoch based on the radionuclide signal alone, he says, “impedes rather than facilitates scientific understanding of human involvement in Earth system change.”

This article is reproduced with permission and was first published on May 21, 2019.