Crawford Lake in Milton, Ontario. In a proposal last year, the lake, whose sediments contained a thousand-year record of human history, would have served as a symbolic starting point for the proposed Anthropocene epoch. (Bonnie Jo Mount/The Washington Post)

The official timekeepers of Earth history are in an uproar after a key scientific panel decided this week that the planet’s geologic timeline should not include a radical new chapter defined by human impacts: the Anthropocene.

In a vote that concluded Monday night, the group of scholars responsible for delineating the past 2.6 million years of geologic history rejected a proposal that would mark the start of the Anthropocene epoch in the mid-20th century, when global trade, nuclear weapons tests and rampant fossil fuel consumption radically altered the Earth.

But Anthropocene advocates — including two leading members of the panel that just voted — say the decision by the Subcommission on Quaternary Stratigraphy violated the rules for naming new geologic time spans. Subcommission chair Jan Zalasiewicz and vice-chair Martin Head on Wednesday called for an investigation into the voting process that could lead to the decision being overturned.

The contested vote, which was first reported by the New York Times, has exposed a deepening rift in the hidebound world of stratigraphy — the science of measuring geologic time.

Researchers overwhelmingly agree that people have transformed the climate and put ecosystems in peril. But most members of the Subcommission on Quaternary Stratigraphy felt this “Age of Humans” should not be rigidly defined as an epoch — a stretch of geologic time that typically spans thousands or even millions of years.

“It suggests that all of a sudden, within my lifetime, the changes that are affecting the planet suddenly appeared,” said Philip Gibbard, a geologist at the University of Cambridge who voted against the Anthropocene proposal. “But humans have in fact been influencing the natural environment for 40,000 years.”

Yet proponents of the new epoch say that humans have caused greater changes in the past seven decades than in the thousands of years that came before — and that the geologic timeline should reflect our overwhelming influence.

“We’ve provided ample evidence that the rate at which humans have an impact on the planet has increased dramatically,” said Francine McCarthy, a professor of earth science at Brock University in Ontario. “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.”

Though artists, activists and academics have used the term “Anthropocene” for decades, the debate over its geologic definition didn’t begin in earnest until 2009, when the body that oversees Earth’s 4.6-billion-year timeline appointed a working group to investigate the idea.

In a search that spanned from mountain summits to the depths of the oceans, the Anthropocene Working Group identified more than 100 distinct markers of how human activities have left an imprint on Earth’s geologic record. Air bubbles in Antarctic ice showed the increasing concentration of carbon dioxide in the atmosphere, they said. Pollen grains at the bottoms of lakes documented how rising global temperatures were changing the compositions of forests. A host of entirely new substances — microplastics, mine waste, the bones of unnaturally large chickens — could be found in almost every corner of the planet.

Though humanity’s environmental impact stretches back millennia, the number and scale of these markers increased dramatically around 1950, the working group concluded. Although these changes unfolded in a geologic eyeblink, studies suggested their effects would be incredibly long-lasting. Even if people disappeared tomorrow, it would take tens of thousands of years for atmospheric carbon concentrations to return to preindustrial levels. And that meant the climate and ecosystems of the Holocene epoch — which began 11,700 years ago at the end of the last ice age — were gone for good.

“All these lines of evidence indicate that the Anthropocene, though currently brief, is … of sufficient scale and importance to be represented on the geologic time scale,” Leicester University geologist Colin Waters, the chair of the Anthropocene Working Group, wrote in an email to The Post.

In a formal proposal submitted in October, the working group suggested that the Anthropocene begin in 1952, when the United States’ first test of a thermonuclear bomb unleashed a plume of radioactive plutonium that circled around the world. A humble Canadian lake whose sediments contained a thousand-year record of human history would serve as the new epoch’s symbolic starting point.

Had the Subcommission on Quaternary Stratigraphy — which oversees the working group — approved the proposal, the Anthropocene would have then worked its way through the layers of geologic bureaucracy, going before the International Commission on Stratigraphy (ICS) before facing a final ratification vote at the International Geological Congress in South Korea this summer.

Unless the ICS overturns the decision, the subcommission’s rejection represents the end of the line for the working group’s current effort. Under the rules of geologic timekeeping, researchers cannot submit another Anthropocene proposal for at least 10 years.

But that doesn’t mean the “Age of Humans” has no place in geology research, said Gibbard, who is also the secretary general of the ICS. He has advocated for the Anthropocene to be defined as a geologic event — a looser term that can describe phenomena that unfold in multiple places at different times.

Though less formal than an epoch, Gibbard said, an Anthropocene event would be no less important. Other events in geologic history include the sudden surge of oxygen in Earth’s atmosphere 2.4 million years ago and the ancient profusion of biological diversity that led to many modern animal lineages.

“The work done by the AWG is excellent,” Gibbard said. “It’s not to be wasted. It’s just to be used differently, that’s all.”