I’ll admit it – I don’t know a whole lot about geology. I think I did take a 101 class in college, but I don’t remember a whole lot from that. As I understand it, geological periods, like Jurassic, Pleistocene etc., are defined by “events” that are recorded in the layers of rock that make up the geologic record. Mass extinctions are common markers, as vast numbers of species simply vanish from the fossil record, but that doesn’t help us if we’re trying to determine whether we are, right now, at a boundary between the Holocene epoch and a new epoch that has been dubbed Anthropocene, in which humans are the dominant force acting on the surface of the planet. Because this is a relatively new idea, work is ongoing to determine whether it’s real/valid as a geological period, and where to draw the line. From what I can tell, the division among those who think it’s real is mainly between whether to start it in the Neolithic era, with the rise of agriculture, or around the start of the Industrial Revolution. From what I can tell, the idea of a more recent starting point is more widely supported, and it’s certainly the one with which I am most familiar.

Resolving this disagreement requires research, of course, but it’s a bit tricky to study a geological layer as it’s forming. All the other ones scientists have studied are long enough ago that they’re literally set in stone.  The Subcommission on Quaternary Strategraphy, a part of the International Commission on Stratigraphy, itself a part of the International Union of Geological Sciences (an NGO that’s part of the International Science Council) set up the Anthropocene Working Group to study the Anthropocene and figure out whether there’s evidence supporting a formal ratification of the Anthropocene as a geological epoch. They’ve been working since 2009, just published their work choosing a Global Boundary Stratotype Section and Point to mark the start of the Anthropocene, for future study. .

Specifically, they’ve chosen Crawford Lake, a little south and west of Toronto, for its “exquisite” sedimentary record, and they are proposing a layer of plutonium from the testing of nuclear weapons in the 1950s, as the starting point of the new epoch:

https://youtu.be/vnhDk0jRJ0s

“The sediments found at the bottom of Crawford Lake provide an exquisite record of recent environmental change over the last millennia,” says Dr Simon Turner, Secretary of the Anthropocene Working Group from UCL. “Seasonal changes in water chemistry and ecology have created annual layers that can be sampled for multiple markers of historical human activity. It is this ability to precisely record and store this information as a geological archive that can be matched to historical global environmental changes which make sites such as Crawford Lake so important. A GSSP is used to correlate similar environmental changes seen in other sites worldwide, so it is critical to have a robust and reproducible record at this type locality.”

The team has gathered core sample sections from a variety of environments around the world, from coral reefs to ice sheets. Samples from a range of these sites were then sent for analysis to the University of Southampton’s GAU-Radioanalytical labs at the National Oceanography Centre in Southampton. Researchers there processed the samples to detect a key marker of human influence on the environment – the presence of plutonium.

Professor Andrew Cundy, Chair in Environmental Radiochemistry at the University of Southampton and member of the Anthropocene Working Group, explains: “The presence of plutonium gives us a stark indicator of when humanity became such a dominant force that it could leave a unique global ‘fingerprint’ on our planet.

“In nature, plutonium is only present in trace amounts. But in the early-1950s, when the first hydrogen bomb tests took place, we see an unprecedented increase and then spike in the levels of plutonium in core samples from around the world. We then see a decline in plutonium from the mid-1960s onwards when the Nuclear Test-Ban Treaty came into effect.”

Other geological indicators of human activity include high levels of ash from coal-fired power stations, high concentrations of heavy metals, such as lead, and the presence of plastic fibres and fragments. These coincide with ‘The Great Acceleration’ – a dramatic surge across a range of human activity, from transportation to energy use, starting in the mid-20th century and continuing today.

From the hundreds of samples analysed, the core from Crawford Lake has been proposed as the GSSP, along with secondary supporting sites that show similar high-resolution records of human impact. Evidence from the sites will now be presented to the ICS, which will decide next year whether to ratify the Anthropocene as a new geological epoch.

I could quibble with this starting point, mainly because by 1950, we were already more than half a century past Arrhenius’ calculation that our CO2 emissions were warming the world. That said, I can’t argue with the utility of the plutonium layer as an excellent global marker, as well as something that will be detectable long into the future. There’s also the fact that defining eras like this is always going to be at least a little arbitrary, determined by convenience or conceit. I talked before about the concept of a “long century”, in which historians include events from the end of one century as part of the beginning of the next, so that the centuries overlap, because our categorization of the past is, itself, fairly arbitrary, and determined by convenience or conceit. The new epoch has to start somewhere, and the point at which we coated the entire planet with plutonium works as well as anything else.

I appreciate Dr. Cundy’s reasoning for Crawford Lake as a site, as well. In the video above he mentions that not only does the sediment provide a clear record of the modern era, it also provides a good record of pre-industrial, and pre-colonial human habitation. I often talk about ways in which the colonial era never really ended, it just changed tactics. That change is as good a reason to mark out a new era as any other, but the similarities are important, because there was a real effort to erase Indigenous Americans from the continent, and in many ways that effort is still ongoing. As we fight for Indigenous rights, and for Land Back, we are also fighting for their history – something that has been under attack along with the people themselves.

We are in a period that is itself defined by the speed at which things are changing. On the one hand, I think that’s just part of the human experience, but on the other, we know, without question, that our species has never experienced a warming event like this in its history. Whether or not the Anthropocene ends up being ratified as and Official Epoch, it will be vital for us to understand this era, if we survive long enough to really learn from it.

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