Scientists unveil the key site that shows we’re in a new climate epoch

The holy grail for understanding the start of the Anthropocene lies at the bottom of a lake in Canada.

An intrepid band of geologists has spent over a decade scouring the planet for the evidence they need to declare we’re living in the Anthropocene, a new chapter in Earth’s history borne of humanity’s impact on the planet.

On Tuesday, they declared they’ve found it.

Earth has gone through distinct geological epochs, vast chunks of time defined by changes in rock layers. To prove that the Anthropocene represents a new one, scientists had to find a “golden spike” — a physical site where the rock, sediment, or ice clearly records the change from a previous chapter in time to a new one. In 2009, they started hunting around the planet and found a range of strong candidates, from a peat bog in Poland to a coral reef in Australia to the ice of Antarctica.

But the Anthropocene Working Group (AWG), as the group is called, wanted to pick a site where the rock record indisputably shows that we’ve left behind the Holocene epoch, which started 11,700 years ago when the last ice age ended.

At last, the geologists say, they’ve found their holy grail.

It’s little Crawford Lake in Ontario, Canada. There, the waters are so deep that whatever sinks down to the floor usually remains without mixing with the upper layers of water, so it stays preserved, offering an unusually good record of geological change.

Since 1950 — which is when the AWG now says the Anthropocene began — the sediment there has been inundated by the byproducts of human activity: plutonium isotopes from the nuclear bombs we’ve donated, ash from the fossil fuels we’ve burned, and nitrogen from the fertilizer we’ve used.

“The record at Crawford Lake is representative of the changes that make the time since the mid-20th century geologically different from before,” said Francine M.G. McCarthy, an earth scientist at Brock University in Ontario and a member of the AWG.

Does this officially mean we’re living in a new epoch?

Not yet.

The Subcommission on Quaternary Stratigraphy will consider the proposal in the next few months. Next, the International Commission on Stratigraphy will vote on whether the Anthropocene deserves to be designated a new epoch. Then the International Geological Congress will make the final determination.

And here’s the thing: many expect that, ultimately, the highest strata of geological timekeepers will reject the idea that we’re living in a new epoch. The debate arguably says more about the purpose of the classification — is it solely scientific, or is it also political? — than it does about some objective moment when the Anthropocene started.

When and how did the Anthropocene start? It’s controversial.

Carving up time is a very messy business. One that scientists tend to fight over — a lot.

Even among those who agree that human activity has ushered in a new epoch, there’s disagreement over when the epoch started. Should we start counting from the Industrial Revolution? From the dawn of agriculture? Some other milestone?

Back in 2019, the AWG voted on whether to designate the middle of the 20th century as the starting point; four voted against, but 29 voted in favor, citing this as the time when we start to see major changes in phenomena like global warming, sea-level rise, ocean acidification, the spread of ash and plastics, and the explosive growth of domestic animal populations.

But some argue that it doesn’t even make sense to recognize our current interval as its own epoch, since it’s incredibly brief in geological time. If the previous epoch, the Holocene, lasted 11,700 years, does it really make sense to give the same designation to an interval that has so far spanned only 73 years?

Erle Ellis, an environmental scientist at the University of Maryland, doesn’t think so. “The Anthropocene is a geological Event, not an Epoch,” he wrote on Twitter in the minutes following the AWG’s announcement.

For the non-geologists: Earth’s professional timekeepers use “epoch” to describe a chunk of time that’s bigger than an “age” but smaller than an “eon,” “era,” or “period.” It’s a technical term with technical criteria, voted on by scientists. By contrast, an “event” is a much looser, more informal term. It can refer to any shock to the Earth’s system, like a mass extinction or an asteroid hitting the planet.

“Narrowing the Anthropocene definition to [a] single year marked by a thin band of sediment in a single lake makes no sense at all,” Ellis wrote.

But whether it makes sense to say we’re now living in a new epoch depends on how you understand the point of these designations.

If you’re a scholar, like an archaeologist or anthropologist, who uses the geologic time scale to orient yourself and situate your work amid unimaginably long spans of time, it may feel unhelpful to have a term usually reserved for stretches lasting millions of years suddenly applied to an interval that’s lasted only decades.

Yet it’s not only scholars who use these labels. The public uses them too. And the term “Anthropocene” is already widely used and understood — in 2020, the musician Grimes even released an album dubbed Miss Anthropocene. The term has become a way to get people to take climate change more seriously. In other words, it’s not just a scientific question — it’s also political.

Some scholars embrace that. The geologist Emlyn Koster, for example, told the New York Times last year that geologists shouldn’t think of defining the Anthropocene as solely the AWG’s business. “I always saw it not as an internal geological undertaking,” he said, “but rather one that could be greatly beneficial to the world at large.”

Others are uncomfortable with the idea of scientists using the “Anthropocene” label to make a political statement about what humanity is doing to the planet.

But the truth is, it’s political either way. If, in the coming months, the highest bodies in geology vote to officially recognize the Anthropocene as a new epoch, that will have political ramifications: it will be read as a clear indictment of humanity’s recklessness on this planet, and a plea to think more about what we owe to future generations. If they decide to withhold the designation, that will also inevitably bear a political meaning.

Ultimately, the fight over “Anthropocene” is not just a fight over a thin band of sediment. It’s a fight over how to make meaning of what we humans are doing on Earth, and to it.