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As many readers are aware, I’ve been writing since 1992 about the notion that we’ve left the Holocene behind — that’s the geological epoch since the end of the last ice age — and entered “a post-Holocene…geological age of our own making,” now best known as the Anthropocene.

That idea has gained a lot of traction, but a formal decision by the International Commission on Stratigraphy is years away. In the meantime, a subsidiary body, the Anthropocene Working Group (because of my early writings, I’m a lay member), has moved substantially from asking whether such a transition has occurred to deciding when.

In a paper published online this week by the journal Quaternary International, 26 members of the working group point roughly to 1950 as the starting point, indicated by a variety of markers, including the global spread of carbon isotopes from nuclear weapon detonations starting in 1945 and the mass production and disposal of plastics. (About six billion tons have been made, with a billon of those tons dumped and a substantial amount spread around the world’s seas.)

You can learn much more in a short, wide-ranging Skype chat I had on Wednesday with the leader of this effort, Jan Zalasiewicz, a geologist at the University of Leicester, who is also lead author on the new paper:

One thing is certain, he told me. There’s little predictability in how things will play out after this anthropogenic jolt, especially in the living world. [More on the “great acceleration” behind the jolt is here.] He alluded to one of the last great junctures in Earth’s history, 65 million years ago, to make the point:

Once you begin to get the many feedbacks bouncing off each other and bouncing off the Earth system, it’s going to be very hard to follow what’s going to happen, particularly biologically…. One could not imagine, at the very end of the Cretaceous, the beginning of the Tertiary, that the mammals — these itty-bitty little squeaky furry things, would take over – effectively taking the position that the dinosaurs held for so long. All we can say is that, for sure, it will be different. We’re going down a different trouser leg of history.

I hope you’ll listen. I apologize for not having time to transcribe the full interview. Perhaps you can add passages that catch your attention in the comment thread.

The group’s paper is posted here (sadly behind a subscription wall except for the abstract): “When did the Anthropocene begin? A mid-twentieth century boundary level is stratigraphically optimal.”

Here’s a short press summary of the paper, and next steps, written for the journal by Zalasiewicz:

Did the Anthropocene begin with the nuclear age?



Scientists identify July 16, 1945, as key time boundary in Earth history

An international group of scientists has proposed the date of the dawn of a new geological age in Earth history – the Age of the Anthropocene. Humans are having such a marked impact on the Earth that they are changing its geology, creating new and distinctive strata that will persist far into the future. This is the idea behind the Anthropocene, a new epoch in Earth history proposed by the Nobel Prize-winning atmospheric chemist Paul Crutzen just 15 years ago. Since then the idea has spread widely through both the sciences and humanities. But if the Anthropocene is to be a geological epoch – when should it begin? Humans have long affected the environment, and ideas as to when the Anthropocene might start range from the thousands of years ago with the dawn of agriculture, to the Industrial Revolution – and even to the future (for the greatest human-made changes could still be to come). Now, members of the international working group formally analyzing the Anthropocene suggest that the key turning point happened in the mid-twentieth century. This was when humans did not just leave traces of their actions, but began to alter the whole Earth system. There was a ‘Great Acceleration’ of population, of carbon emissions, of species invasions and extinctions, of earth moving, of the production of concrete, plastics and metals. It included the start, too, of the nuclear age, when artificial radionuclides were scattered across the Earth, from the poles to the Equator, to be leave a detectable signal in modern strata virtually everywhere. The proposal, signed up to by 26 members of the working group, including lead author Dr Jan Zalasiewicz, who also chairs the working group, and Dr Mark Williams of the University of Leicester’s Department of Geology, is that the beginning of the Anthropocene could be considered to be drawn at the moment of detonation of the world’s first nuclear test: on July 16th 1945. The beginning of the nuclear age, it marks the historic turning point when humans first accessed an enormous new energy source – and is also a time level that can be effectively tracked within geological strata, using a variety of geological clues. Dr Zalasiewicz said: “Like any geological boundary, it is not a perfect marker – levels of global radiation really rose in the early 1950s, as salvoes of bomb tests took place. But it may be the optimal way to resolve the multiple lines of evidence on human-driven planetary change. Time – and much more discussion- will tell.” This year, the Anthropocene Working Group will put together more evidence on the Anthropocene, including discussion of possible alternative time boundaries. In 2016, the group hopes to make recommendations on whether this new time unit should be formalized and, if so, how it might be defined and characterized. Authors: Zalasiewicz, J., Waters, C.N., Williams, M., Barnosky, A.D., Cerreata, A., Crutzen, P., Ellis, E., Ellis, M.E., Fairchild, I.J., Grinevald, J., Haff, P.K., Hajdas, I., Leinfelder, R., McNeill, J., Odada, E.O., Poirier, C., Richter, D., Steffen, W., Summerhayes, C., Syvitski, J.P.M., Vidas, D., Wagreich, M., Wing, S.L., Wolfe, A.P., An, Z. & Oreskes, N.

I’d like to close by reprising the tail end of a post from 2011, called “Embracing the Anthropocene.” It’s more relevant than ever, and relates to my recent exchanges with Clive Hamilton, the Australian ethicist, and Elizabeth Kolbert, author of “The Sixth Extinction,” on whether it’s possible to have a “good Anthropocene.” Kolbert’s Twitter post last spring nicely captured their view:

2 words that probably should not be used in sequence: “good” & “anthropocene.” Very smart essay by @CliveCHamilton: //t.co/VAqnJvTBgJ — Elizabeth Kolbert (@ElizKolbert) 17 Jun 14

Here’s the end of my 2011 piece laying out my take on this issue: