Geology’s Timekeepers Are Feuding

“It’s a bit like Monty Python.”

A geologist works on a sedimentary rock record. (Roger Ressmeyer / Corbis / Getty)

“What the fuck is the Meghalayan?” asked Ben van der Pluijm, a geologist.

Whatever the Meghalayan is, we live in it now.

Earlier this week, the International Commission on Stratigraphy announced that the current stretch of geological time, the Holocene Epoch, would be split into three subdivisions.

This is particularly noteworthy to the human species, as we have been living in the Holocene for the last 12,000 years. After this announcement, we still live in that epoch, but we also live in the youngest of these new subdivisions: the Meghalayan Age.

This new slice of time started roughly 4,250 years ago and extends to the present. In other words, we have been living in the Meghalayan for quite a long time, even if it didn’t have a formal name.

For decades, this has been the kind of technical declaration that even most geologists could safely ignore.

But lately, the study of geological timescales has attracted far more public attention—and scholarly f-bombs. Stratigraphy, the effort to name and describe rock layers, has become the site of a proxy battle over climate change, environmental change, and how deeply the natural sciences should integrate with history and politics.

The International Commission on Stratigraphy, or ICS, is the global governing body that formally names geological eras, associating each rock layer with a specific stretch of time. For instance, the ICS formally named and identified the Jurassic, to the immense benefit of paleontologists and fictional theme-park developers everywhere.

Stratigraphers are not known for their public-relations acumen. “A lot of this timescale work used to be completely below the radar. It was done by small, dedicated groups and it never got the headlines, ” says Jan Zalasiewicz, a professor of paleobiology at the University of Leicester. “Most geologists think of it as really dull work—you know, it’s a bit like eating your greens, someone’s got to do it.”

Stratigraphers were something like the tax attorneys of geology. Even the hardiest geologists—celebrated professionals who thrill to spend hours in the lab carefully measuring small cylinders of dirt—blanched at the tedium of stratigraphy.

But then, in 2000, the Nobel Prize-winning chemist Paul Crutzen won permanent fame for stratigraphy. He proposed that humans had so throughly altered the fundamental processes of the planet—through agriculture, climate change, and nuclear testing, and other phenomena—that a new geological epoch had commenced: the Anthropocene, the age of humans.

It is a stirring idea: that humans are not a momentary blip in the long procession of Earth’s history, but a new and fundamental driver of planetary change, equal in stature to volcanoes and tectonic plates. Suddenly, a much wider set of researchers—including sociologists and critical theorists—began studying the layers of geological time.

“The Anthropocene has woken up an interest in the timescale among a wider community,” Zalasiewicz told me. These newcomers “don’t quite always appreciate quite what the science is and what the discipline is, because it has its own quirks, its own traditions, its own methodologies.”

Zalasiewicz should know. He is the chair of the Anthropocene working group, which the ICS established in 2009 to investigate whether the new epoch deserved a place in stratigraphic time.

In 2015, the group announced that the Anthropocene was a plausible new layer and that it should likely follow the Holocene. But the team has yet to propose a “golden spike” for the epoch: a boundary in the sedimentary rock record where the Anthropocene clearly begins.

This week’s announcement is not actually about the Anthropocene: The ICS subdivided the Holocene this week, and it said nothing about the Anthropocene. Except that to some geologists, the subdivision was entirely about the Anthropocene.

“I was stunned by this whole thing,” says van der Pluijm, who is a professor of geology at the University of Michigan. “I think they’ve trivialized the Anthropocene by doing this.”

Van der Pluijm believes that the ICS slighted the Anthropocene by chopping the Holocene into three. The timescale “shouldn’t be cut into smaller and smaller pieces,” he told me. “This is a bit of a silly activity. It’s very Monty Python—the Ministry of Silly Cuts.”

Above all, he thinks the new subdivisions make the Anthropocene seem less prominent than it is. “Geologists are not a bunch of fools who do not understand the changes that are taking place,” he said. “The changes that are happening now are very large—just take sea-level rise, for example. It’s important that people think [stratigraphy] is not just a bunch of hobby talk.”

At stake is what to call the most recent 11,700 years of natural history. For decades, geologists have named this stretch of time the Holocene epoch. It seemed to have clear boundaries: It began as the great, continent-spanning glaciers of the last Ice Age receded, and it ran to the present day.

By normal geological standards, 11,700 years is vanishingly brief. Most epochs run for millions of years. The Upper Cretaceous—the last epoch when non-avian dinosaurs stalked the Earth—lasted 34 million years, or almost 3,000 times longer than the Holocene.

But the Holocene is everything for humans. It encompasses all of human history and much of our prehistory: the flourishing of the first cities, the revelation of every major religion, and the invention of the rifle, the rice paddy, and the radio.

Arsh Raziuddin / The Atlantic

Officially, the Holocene is still running today. You have lived your entire life in the Holocene, and the Holocene has constituted the geological “present” for as long as there have been geologists.

But if we now live in a new epoch, the Anthropocene, then the ICS will have to chop the Holocene somewhere. It will have to choose when the Holocene ended, and it will move some amount of time out of the purview of the Holocene working group and into that of the Anthropocene working group.

This is politically difficult. And right now, the Anthropocene working group seems intent on not carving too deep into the Holocene. In a paper published earlier this year in Earth-Science Reviews, the Anthropocene working group’s members strongly imply that they will propose starting the new epoch in the mid-20th century.

Under this scenario, the Holocene would run from the end of the last Ice Age to roughly 1945 or 1950. Then the Anthropocene would commence. Like so:

Arsh Raziuddin / The Atlantic

There are several good arguments for starting the Anthropocene around 1950. The first radiometric signatures of atomic weapons will appear in the rock record around 1945. The period after World War II also saw the “Great Acceleration,” when countries around the world industrialized, and car culture came to the United States and Europe. It was then that gargantuan amounts of greenhouse gas began streaming into the atmosphere every year.

But there are rival claims to the Anthropocene’s start date. Some geologists want to peg it at 1800, when the Industrial Revolution began. Others say it started around 1492, as Europeans started to ferry animals, plants, diseases, and people between the continents.

Some geologists argue that the Anthropocene started even earlier: perhaps 4,000 or 6,000 years ago, as farmers began to remake the land surface.

“Most of the world’s forests that were going to be converted to cropland and agriculture were already cleared well before 1950,” says Bill Ruddiman, a geology professor at the University of Virginia and an advocate of this extremely early Anthropocene.

“Most of the world’s prairies and steppes that were going to be cleared for crops were already gone, by then. How can you argue the Anthropocene started in 1950 when all of the major things that affect Earth’s surface were already over?”

Van der Pluijm agreed that the Anthropocene working group was picking 1950 for “not very good reasons.”

“Agriculture was the revolution that allowed society to develop,” he said. “That was really when people started to force the land to work for them. That massive land movement—it’s like a landslide, except it’s a humanslide. And it is not, of course, as dramatic as today’s motion of land, but it starts the clock.”

These debates matter for more than just Anthropocene fans. If you come to believe that the Anthropocene started 6,000 years ago, then it seems like a slight when the Holocene introduces a new cut in time there.

Even if that was never what slicing the Holocene was about. “I definitely don’t think this was about intentionally undercutting the Anthropocene,” says Max Berkelhammer, a professor at the University of Illinois at Chicago who co-authored the Holocene proposal.

Instead, his colleagues advanced the Holocene proposal in order to bring clarity to scientific debate. For decades, climatologists have talked about periods of time within the Holocene—like, say, “the late Holocene”—without ever specifying when, exactly, they meant. “Some people say the late Holocene was warm, other people say the late Holocene was cold, and they both might be right, because they’re using this term late Holocene inconsistently,” Berkelhammer told me.

This muddle had to stop. The Holocene comes up constantly in discussions of modern global warming. Geologists and climate scientists did not make their jobs any easier by slicing it in different ways and telling contradictory stories about it.

So Mike Walker, a professor at the University of Wales, led a team to make the three new cuts in the rock record.

The Early Holocene starts 11,700 years ago, as the last Ice Age ended. Stratigraphers will call it the Greenlandian Age, because its “golden spike” is taken from an ice core drilled from Greenland’s ice sheet.

The Middle Holocene begins roughly 8,330 years ago, during a sudden and unexplained outbreak of cold temperatures in the Northern Hemisphere. It’s named the Northgrippian Age, after the scientific expedition that found its golden spike: the Northern Greenland Ice Core Project, or NGRIP.

The Late Holocene starts about 4,250 years ago, during a massive drought that struck Eurasia and destroyed several ancient societies. The team found clear evidence of that event in a cave in Meghalaya, a state in northeastern India, so the age is termed the Meghalayan.

Arsh Raziuddin / The Atlantic

It takes years for any stratigraphic proposal to join the formal ICS timescale. This Holocene proposal had to be approved by super-majority vote by four different committees. It went before the Holocene working group; then the Quaternary working group, which oversees the last 2.8 million years; and then the ICS board as a whole.

Finally, the International Union of Geological Sciences, the global governing body for geologists, reviews the proposal and approves it.

This process started almost 10 years ago. For this reason, Zalasiewicz, the chair of the Anthropocene working group, said he wasn’t blindsided by the new subdivisions at all. In fact, he voted to adopt them as a member of the Quaternary working group.

“Whether the Anthropocene works with a unified Holocene or one that’s in three parts makes for very little difference,” he told me.

In fact, it had made the Anthropocene group’s work easier. “It has been useful to compare the scale of the two climate events that mark the new boundaries [within the Holocene] with the kind of changes that we’re assessing in the Anthropocene. It has been quite useful to have the compare and contrast,” he said. “Our view is that some of the changes in the Anthropocene are rather bigger.”

Stan Finney, the secretary-general of the International Union of Geological Sciences, said he was thrilled by the new subepochs.

“There’s this huge swell of young people who love the names and I think the names are catching on now, very quickly,” he told me, speaking by phone from his wife’s apartment in Madrid. “We’ve had more than 100,000 looks at the [geological timescale] chart on our IUGS website in the last five days.”

Finney agreed that the new subdivisions were not meant to slight the Anthropocene working group. “People have tried to say, ‘Oh, this was hidden, it was not transparent, it was dumped on the world. There’s a bitter fight between the Holocene and the Anthropocene working group,’” he said.

But Zalasiewicz’s support for the new subdivisions proved this was not the case, he told me. “The chairman [of the Anthropocene working group] voted to approve these subdivisions, and he did it back in 2016. So there’s no collusion. Nothing’s hidden. Those charges, they’re lies.”

He then criticized the Anthropocene working group at length, accusing them of committing ethical lapses and of courting an unseemly amount of press coverage.

“They have an incredible press campaign that has misrepresented the science and history of the units of stratigraphy,” he said.

He charges that the Anthropocene working group has fixated on finding a “golden spike” in time to start the new epoch. They have failed to find “a stratigraphic unit,” a rock layer that associates with the Anthropocene.

For contemporary stretches of geological time, the ICS will also accept layers of any material that forms sedimentary material every year, like an ice core, a stalagmite, or tree rings. But Finney says that the Anthropocene working group has failed to provide any of these things.

“Holocene had an incredible stratigraphic proposal, and then they gave it to us for feedback,” he said. “Anthropocene hasn’t started that process. It’s been 10 years, a multitude of papers and press release have been published, and can I ask—for what?”

“Anthropogenic climate change is real, there’s no doubt about that,” Finney said. But he said that geologists didn’t need a new “core stratigraphic unit” to discuss this change: They could just say the year when things happened. “If you find a pile of garbage somewhere, then ‘That’s the Anthropocene!’ No, that’s a garbage dump,” he said. “It was done in 1940.”

Zalasiewicz said that he and his colleagues were going as fast as they could. When the working group group began its work in 2009, it was “really starting from scratch,” he told me.

While other working groups have a large body of stratigraphic research to consider, the Anthropocene working group had nothing. “We had to spend a fair bit of time deciding whether the Anthropocene was geology at all,” he said. Then they had to decide where its signal could show up. Now, they’re looking for evidence that shows it.

“If there’s not a good scientific case, we’ll push it over ourselves and let it fall. If we think it’s good to propose formally, then it’s up to the stratigraphic bodies above us to make the decision,” he said.

Part of the controversy here stems from a simple fact: It is strange that geologists pull out the Holocene for special treatment at all.

It is easy to write that the Holocene began “when the last Ice Age ended,” but this misstates Earth’s recent geological history. Over the last 2.8 million years, there have been many Ice Ages: Enormous glaciers have descended from the Arctic, remade vast tracts of Eurasia and North America, and then receded after 100,000 years. After 40,000 years of warmer temperatures, the glaciers descend again.

This cycle of “glacials” and “interglacials” has played out about 50 times over the last several million years. When the Holocene began, it was only another interglacial—albeit the one we live in. Until recently, glaciers were still on schedule to descend in another 30,000 years or so.

Yet geologists still call the Holocene an epoch, even though they do not bestow this term on any of the previous 49 interglacials. It get special treatment because we live in it.

Much of this science is now moot. Humanity’s vast emissions of greenhouse gas have now so warmed the climate that they have offset the next glaciation. They may even knock us out of the ongoing cycle of Ice Ages, sending the Earth hurtling back toward a “greenhouse” climate after the more amenable “icehouse” climate during which humans evolved.

For this reason, van der Pluijm wants the Anthropocene to supplant the Holocene entirely. Humans made their first great change to the environment at the close of the last glaciation, when they seem to have hunted the world’s largest mammals—the wooly mammoth, the saber-toothed tiger—to extinction. Why not start the Anthropocene then?

He would even rename the pre-1800 period “the Holocene Age” as a consolation prize:

Arsh Raziuddin / The Atlantic

“Humans have redistributed species around the world! We do what plate tectonics used to do, and move species around,” van der Pluijm said. “In the geologic record, a few million years from now, you will suddenly see bones all around the world that never used to be there.”

He continued. “The point is, if you were a geologist a few million years from now, you would have no difficulty identifying all kinds of characteristics [happening in our time] that are different from what happened before. Geologists in the future will recognize this as a time of major change.”

Finney has a special loathing for this idea. “Well, we’re not making a timescale for people a million years from now,” he told me. “I hear that argument from scientists, and I have to shake my head. The IUGS is not making a unit for someone to come back to in a million years.”

He also defended the Holocene as an unusually short epoch. Geological units get shorter as they approach the modern era, he told me, because scholars have more information about recent events. “As you get to the present, you have better resolution,” he said.

Zalasiewicz said he would not start the Anthropocene too early in time, as it would be too work-intensive for the field to rename such a vast swath of time. “The early-Anthropocene idea would crosscut against the Holocene as it’s seen by Holocene workers,” he said. If other academics didn’t like this, they could create their own timescales and start the Anthropocene Epoch where they choose. “We have no jurisdiction over the word Anthropocene,” he said.

Ruddiman, the University of Virginia professor who first argued for a very early Anthropocene, now makes an even broader case. He’s not sure it makes sense to formally define the Anthropocene at all. In a paper published this week, he objects to designating the Anthropocene as starting in the 1950s—and then he objects to delineating the Anthropocene, or indeed any new geological epoch, by name. “Keep the use of the term informal,” he told me. “Don’t make it rigid. Keep it informal so people can say the early-agricultural Anthropocene, or the industrial-era Anthropocene.”

The problem with naming a new epoch, he told me, is that no one cares.

“I’m going to take some serious crap for this article,” he said. “It’s going to insult some old-school geologists, but doing these formal definitions just isn’t the way that practicing geologists do things. The community just doesn’t care about these definitions.”

He predicted that no one would use these new Holocene subdivisions. Recently, he researched how many geology textbooks refer to the subdivisions within the Pleistocene, the 2.8-million-year epoch that preceded the Holocene. According to the ICS, the Pleistocene is split into four ages. But he found that only one textbook even alluded to them.

“This is the age of geochemical dating,” he said. Geologists have stopped looking to the ICS to place each rock sample into the rock sequence. Instead, field geologists use laboratory techniques to get a precise year or century of origin for each rock sample. “The community just doesn’t care about these definitions,” he said.

Take the Meghalayan, for instance, our new home in time. Geologists and climate scientists already call the mega-drought that initiated the Meghalayan the “4.2-kiloyear event,” he said. They won’t change their ways because it happens to have a new, ICS-approved name.

“I’m not going to remember what they named it,” he said. I’m never going to use the name, and I’m guessing most scientists will not. To me? It’s silly.”