Over a month after the vote, the think pieces on the "rejected" Anthropocene are still coming strong, so I wanted to take a moment to (finally!) offer some background and thoughts about the vote, the process, and what it all means.
Geologists define different intervals in Earth's past so we can share a common language. Earth's 4.5 billion year history is divided into a series of eons (longest), eras, periods, epochs, and ages (shortest), based on visible changes in rock layers and fossil ecosystems.
For example, the Cenozoic Era began 66 million years ago with the impact that killed the dinosaurs. Within that, the Paleocene (66 to 56 mya) was the first epoch within the Paleogene Period (66 to 23 mya). Each is defined by rock layers that record extinctions and climate events.
The K-Pg boundary layer that separates the age of dinosaurs with the start of the Paleogene is a visible layer in rocks around the world that marks a single moment when the Chicxulub asteroid hit Earth (friendly reminder to Google Chicxulub if you haven't). You can touch it!
Some boundaries are clear lines in the rock record; others are determined by when fossil organisms show up or go extinct. Most “boundaries” span millennia, and represent the end of one geologic unit and the beginning of another. So, how do geologists decide on boundaries?
Today, the geologic timescale is governed by the International Committee on Stratigraphy, a group of geologists whose job is to identify boundaries in the geologic record and agree upon the criteria for identifying them. They review proposals to add or change existing boundaries.
In the geologic timescale, these divisions are called Global Boundary Stratotype Sections and Points (GSSPs). The GSSP is a “golden spike” that identifies the lower boundary of each geologic unit, usually identified by the first appearance of a fossil type.
Once a GSSP has been selected by the Commission, a “golden spike” (not really gold) is drilled into the spot, similar to how species have a “type specimen” in biology. This serves as a reference point for future geologists. Here's the Ediacaran GSSP, which started 635 mya.
GSSP's have very strict criteria. They must be visible, unambiguous, ideally have multiple lines of fossil and geochemical evidence, be datable, have regional and global representation, not be deformed by tectonics or other processes, and freely accessible to visit and research.
You can read more about the criteria here, and see the map of the distribution of GSSPs (which notably are not easily accessible to researchers in the southern hemisphere, reflecting research biases and not the availability of the rock record). https://t.co/5eUsMIkgAN
So now, we come to the Anthropocene! This isn't a new concept, and like many ideas, it has multiple origins. As far back as 1938, Russian geologist Vladimir Vernadsky (1863-1945), proposed the term “Noosphere” to describe “scientific thought as a geological force.”
And as early as the 1960's, Soviet scientists were using the term "Anthropocene" (or, its Russian equivalent) to describe our current geologic period, the Quaternary (2.588 million years ago - today), since modern humans evolved during this time.
Lake ecologist Eugene Stoermer first used "Anthropocene" in the 80's to describe the evidence of the impacts of humans on natural ecosystems. But the term is usually associated with atmospheric chemist Paul Crutzen, who used it in a speech in 2000 to suggest a new geologic epoch.
Interest in the Anthropocene was growing, and in 2009, an Anthropocene Working Group (AWG) was established as part of the Subcommission on Quaternary Stratigraphy (SQS), the division of the ICS responsible for the geologic record of the last 2.588 million years. Acronym salad!
The AWG's job was to evaluate proposals for a candidate GSSP (golden spike) to identify the end of the Holocene (our current epoch, which started ~11,700 years ago coincident with the timing of our current interglacial warm period) and the start of the "age of humanity."
(As a side note, there's nothing geologically unique about the Holocene; there have been many interglacials throughout the Quaternary Period. The only thing different about this one is, well, us.)
There have been dozens of proposed candidates, including the extinction of ice age megafauna, atmospheric changes associated with agriculture and deforestation ~5000 years ago, nuclear testing in 1945, the beginning of mining ~3000 years ago, the age of plastics ~1950...
Side note: the AWG was not particularly diverse-- it was primarily geologists, largely did not involve social scientists or those in the humanities, was mostly white, and famously came under fire in 2014 for having few women (they added more). https://t.co/Jk36T2MMK2
The AWG spent years evaluating, refining, and debating different candidate GSSPs, as each one was held up against the criteria and found wanting in some way. What might geologists use to define our era millions of years from now?
By 2016, the group had decided that only 20th century examples would be considered, which many on and outside the AWG disagreed with. Archaeologists and paleoecologists argued that the impacts of people on ecosystems, which accelerated with colonialism, extended further back.
Last July, the AWG announced that they had selected a sediment core from Crawford Lake in Canada recording the "Great Acceleration" of environmental impacts in the 50's as the proposed GSSP for the Anthropocene. https://t.co/BwlxC857dG
The AWG's proposal was submitted to the Subcommission on Quaternary Stratigraphy, where it was rejected by a wide margin; the SQS cited the lake's shallow sedimentary record and the extremely recent proposed start date of 1952 as reasons for the rejection.
This is important: despite the fact that it has been widely reported that geologists have rejected the idea that we are in an age of humanity, or even that humans have had a significant impact on our planet, that's not actually what happened. The SQS only rejected 1952 as a GSSP.
Some members of the AWG were unhappy with the vote, but the International Commission on Stratigraphy and the International Union of Geological Sciences both confirmed the Subcommission on Quaternary Stratigraphy's decision by nearly unanimous vote.
In a announcement about their vote, the IUGS stated: "Despite its rejection as a formal unit of the Geologic Time Scale, Anthropocene will nevertheless continue to be used not only by Earth and environmental scientists, but also by social scientists, politicians and economists...
...as well as by the public at large. It will remain an invaluable descriptor of human impact on the Earth system." Again: geologists did not reject the concept of the Anthropocene, or humans as a dominant shaping force on our planet.
Under the rules, researchers can't propose a new Anthropocene GSSP for another decade, but that doesn't mean the Anthropocene is dead as a concept. It's widely used across disciplines, and may be most effective that way; a narrow geologic definition might just confuse things.
As @erleellis (a member of the AWG from 2009-2023) is wrote, the Anthropocene "was rejected for a variety of reasons, none of them related to the fact that human societies are changing this planet. In fact, the opposite is true." https://t.co/nnLGOu9EXF
*the AWG's Anthropocene Epoch proposal was rejected (not the concept of the Anthropocene, which I hope I made clear throughout this thread!)