Scientists Take New Step to Declare the Anthropocene, the Age of Humans

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The official timeline of Earth’s history — from the oldest rocks to dinosaurs and the rise of primates, from the Paleozoic to the Jurassic and every point before and after — could soon include the age of nuclear weapons, of man-made climate change and the proliferation of plastics, garbage and concrete across the planet.

In short, the present.

Ten thousand years after our species began to form primitive agrarian societies, a panel of scientists took a big step this past day 17 to declare a new geological time interval: the Anthropocene, the age of humans.

Our current geological epoch, the Holocene, began 11,700 years ago with the end of the last great ice age. The 35 or so scholars on the panel seem to be close to endorsing that we have actually spent the last few decades in an entirely new unit of time, characterized by human-induced planetary-scale changes that are incomplete but ongoing.

“If you were in the 1920s, your attitude would be, ‘Nature is too big for humans to influence,'” said Colin N. Waters, a geologist and chair of the Anthropocene Working Group, the panel that has deliberated on the issue since 2009. The past century has changed that thinking, Waters said. “It was a shock event, a bit like an asteroid hitting the planet.”

Working group members completed the first of a series of internal polls on details, including when exactly they believe the Anthropocene began, on the 17th. Once those votes are over, which could be in the next quarter, the panel will present its final proposal to three other committees of geologists whose votes will either make the Anthropocene official or reject it.

Sixty percent of each committee will need to approve the group’s proposal for it to move on to the next. If it fails any of these, the Anthropocene may not have another chance to be ratified for years.

If it made it to the end, however, the altered timeline of geology would officially recognize that humanity’s effects on the planet were so important that they closed the previous chapter in Earth’s history. I would recognize that these effects will be noticeable in rocks for millennia.

“I teach the history of science — you know, Copernicus, Kepler, Galileo,” said Francine McCarthy, an Earth scientist at Brock University in Canada and a member of the working group. “We’re really doing this,” she said. “We are living the history of science.”

Still, there are criticisms of the Anthropocene, even though we all have first-hand familiarity with it, or perhaps because of that.

Stanley C. Finney, secretary general of the International Union of Geological Sciences, worries that the Anthropocene has become a way for geologists to make a “political statement.”

In the vast expanse of geological time, he notes, the Anthropocene would be a tiny blip. Other units of geological time are useful because they guide scientists through stretches of deep time that have left no written records, only scattered scientific observations. The Anthropocene, on the other hand, would be a time in Earth’s history that humans have already extensively documented.

“For human transformation, we don’t need these terminologies, we have the exact years,” said Finney, whose committee would be the last to vote on the working group’s proposal if it goes that far.

Martin J. Head, a working group member and an Earth scientist at Brock University, argues that refusing to recognize the Anthropocene would also have political repercussions.

“People would say, ‘Well, does that mean the geological community is in denial that we’ve changed the planet drastically?'” he said. “We would have to justify our decision anyway.”

Philip L. Gibbard, a geologist at the University of Cambridge, is secretary general of another of the committees that will vote on the working group’s proposal. He has serious concerns about how the proposal is shaping up, concerns that the wider geological community shares, in his view.

“It won’t be easy,” he said.

‘A messy and controversial business’

Like zoologists who regulate the names of animal species or astronomers who decide what counts as a planet, timekeepers in geology work conservatively by default. They establish rankings that will be reflected in academic studies, museums and textbooks for generations to come.

“Everyone criticizes the Anthropocene Working Group because they took so long,” said Lucy E. Edwards, a retired scientist with the US Geological Survey. “In geological time, that’s not much.”

Drawing lines in Earth time has never been easy. The rock record is full of gaps, “a jigsaw puzzle with many pieces missing,” as Gibbard puts it. And most changes on a global scale happen gradually, making it difficult to tell when one chapter ends and the next begins. There weren’t many times when the entire planet changed all at once.

“If a meteor hits the Yucatan Peninsula, it’s a pretty good marker,” Edwards said. “But other than that, there’s virtually nothing in the geological world that’s the best line.”

The beginning of the Cambrian Period, around 540 million years ago, saw the Earth explode with an astonishing diversity of animal life, but its exact starting point has been disputed for decades. A long-running controversy led to the redesign of our current geological period, the Quaternary, in 2009.

“It’s a messy and controversial business,” said Jan A. Zalasiewicz, a geologist at the University of Leicester. “And, of course, the Anthropocene brings a whole new range of dimensions to the confusion and disputes.”

Humanity’s Fingerprint

It took a decade of debate – in emails, scholarly articles and meetings in London, Berlin, Oslo and beyond – for the Anthropocene Working Group to define a fundamental aspect of its proposal.

In a 29-4 vote in 2019, the group agreed to recommend that the Anthropocene begin in the mid-20th century. This is when human populations, economic activity and greenhouse gas emissions began to skyrocket around the world, leaving indelible traces: plutonium isotopes from nuclear explosions, nitrogen from fertilizers, ash from power plants.

The Anthropocene, like almost all other geological time intervals, needs to be defined by a specific physical location, known as the “golden peg”, where the rock record clearly differentiates it from the previous interval.

After years of searching, the working group ended on the 17th by voting on nine candidate sites for the Anthropocene. They represent the range of environments in which human effects are recorded: a peat bog in Poland, the ice of the Antarctic Peninsula, a bay in Japan, a coral reef off the coast of Louisiana (USA).

Many scholars are still unsure whether the mid-20th century limit makes sense. It’s awkwardly recent, especially for archaeologists and anthropologists who would have to start referring to World War II artifacts as “pre-Anthropocene.”

And the use of nuclear bombs to mark a geological gap seems abhorrent to some scientists, or at least irrelevant. Radionuclides are a convenient global marker, but they say nothing about climate change or other human effects, said Erle C. Ellis, an ecologist at the University of Maryland.

Using the Industrial Revolution might help, but that definition would still leave out millennia of changes wrought on the planet by agriculture and deforestation.

called to attention

Canonizing the Anthropocene is a wake-up call, said Naomi Oreskes, a member of the working group. For geology, but also for the rest of the world.

“I was raised in a generation where we were taught that geology ended when people showed up,” said Oreskes, a historian of science at Harvard University. The Anthropocene heralds that “in fact, human impact is part of geology as a science,” she said. It requires that we recognize that our influence on the planet goes beyond the surface level.

But Cambridge’s Gibbard worries that by trying to add the Anthropocene to the geological time scale, the working group may actually be downplaying the concept. Strict timeline rules force the group to impose a single starting point on a sprawling story, which unfolded at different times in different places.

He and others argue that the Anthropocene deserves a more flexible geological label: an event. Events do not appear on the timeline; no bureaucracy of scientists regulates them. But they have been transformative for the planet.

Translated by Luiz Roberto M. Gonçalves

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