For nearly 15 years, a panel of scholars has been mulling over a big question: Has our species transformed the planet so much that we’ve plunged it into a new interval of geologic time?

On Tuesday, the panel announced a key part of its case to state that we had. The group said it chose an isolated lake in Ontario to represent the start of the Anthropocene epoch, a potential new chapter in Earth’s 4.6 billion-year history that could soon sit alongside the Cambrian, Jurassic and the Cretaceous in marking important planetary periods. to change

The scientists chose Crawford Lake over 11 other candidate sites, they said, because it contained the clearest and most obvious evidence of humanity’s influence on the global rock record, including plutonium from nuclear explosions, ash from accelerated burning of fossil fuels fuels and nitrogen from increased fertilizer. to use

“The record at Crawford Lake is representative of the changes that make time since the mid-20th century geologically different than before,” said Francine MG McCarthy, an earth scientist at Brock University in St. Louis. Catharines, Ontario, and a member of the Anthropocene Working Group, the panel that since 2009 has been debating whether, and how, to give the human age a place in the official geological timeline.

Canonizing the Anthropocene would claim that humans have changed the Earth so significantly in recent decades that our current geological epoch, the Holocene, which began 11,700 years ago and fostered the conditions for complex human civilizations to emerge, has definitively ended.

Scientists’ final verdict on the Anthropocene will dictate nomenclature used in academic studies, textbooks and museums for generations to come, and will help shape humanity’s understanding of its place on Earth.

Preparing for such a monumental statement was anything but simple. And there’s still a ways to go before it becomes official.

After the working group writes its formal proposal for recognition of the Anthropocene epoch based on the site in Canada, three more commissions of geologists will vote on it, a process that could begin this fall. Sixty percent of each committee will have to approve the proposal in order for it to advance to the next. Ratification by anyone is by no means guaranteed.

In fact, two of the roughly three dozen members of the Anthropocene Working Group resigned recently because they disagreed with the panel’s approach. Geologists on the other voting committees might prove similarly hesitant to enshrine a period that is still a mere toddler by Earth-time standards, no matter how consequential it has been for the planet.

“It’s going to be a really bumpy ride,” said Jan A. Zalasiewicz, a geologist at the University of Leicester in England and a member of the working group. “I’m not smart about the chances. But it is important science.”

In 2019, the panel agreed, after a decade of debate, to recommend that the new era began in the mid-20th century, which is when globalization, industrialization and energy consumption began to accelerate. At the end of last year, the members of the group began to vote on a physical location, known as the “golden spike”, where the rock record clearly divides the Anthropocene from the Holocene before it.

Almost all geologic time units have golden spikes, and they’re not just symbolic. Each must contain geochemical markers so distinctive that, when scientists find unknown rocks in other places, they can match the markers to determine approximately how old they are.

It took three votes, from last fall to spring, for the Anthropocene panel to select Crawford Lake, whose waters are so deep that whatever falls to the bottom is preserved in the mud, accumulating over time into a tree-ring-like . a record of planetary change. The other finalists were Sihailongwan, a volcanic crater lake in China, and Beppu Bay, of Kyushu in Japan.

“It was an extremely close call,” said Colin N. Waters, the chairman of the task force. “A lot of careful thought went into this.”

In the coming months, the panel will also select auxiliary sites that could help geologists locate the boundary between the Holocene and the Anthropocene in other environments, not just lake beds. Like corals, for example. Or peat bogs.

But to Philip L. Gibbard, a geologist at the University of Cambridge, it feels as if the group is doing this careful work to create a definition of the Anthropocene that will be meaningless upon arrival to many people.

Dr. Gibbard joined the panel at its inception in 2009. But over the past few years, he felt his views drift away from those of the rest of the group, he said. Eventually, he and another member — Matt Edgeworth, an archaeologist — resigned this year “out of nowhere,” he said.

As a term, “Anthropocene” long ago spread out of the realm of natural science, and the archaeologists, anthropologists and artists who use it are unlikely to listen to geologists who insist that it applies only to the world after World War II. , said Dr. Gibbard. “We’re not cops,” he said. “We cannot tell colleagues in social sciences what to do.”

The strict rules of the geological timeline also require the new era to have a fixed starting point, which Dr. Gibbard believes would be detrimental to the unfolding story of humanity’s transformation of the planet.

Dr. Waters, the chairman of the task force, said he had known Dr. Gibbard for two decades, and that they had always gotten along well. Now, after their split over the Anthropocene, and with the tone of their emails becoming increasingly sour, he wonders if Dr. Gibbard will even speak to him the next time they’re at the same scientific conference, Dr. Waters said.

“There is a sense of emotion to this that is strange,” said Dr. Waters.

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