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The Anthropocene Work Group have proposed that Crawford Lake in Canada serve as a reference site for studying the Anthropocene as a possible geological epoch.
Prof Crispin Halsall, Professor of Environmental Organic Chemistry at Lancaster University, said:
“Just as oil and coal deposits mark the Carboniferous Period some ~300Million years ago, so anthropogenic modification of this fossilised carbon to create plastic polymers and ‘forever’ chemicals, alongside artificial radionuclides, leaves an indelible marker of human activity on the planet.”
Prof Jan Zalasiewicz, Emeritus Professor of Palaeobiology, University of Leicester, said:
“The Anthropocene Working Group have, over the past decade, amassed much evidence to show beyond reasonable doubt that the Anthropocene as conceptualized by Paul Crutzen in 2000 is real, with massive post-1950 human impacts pushing the Earth out its generally stable Holocene state towards a hotter, polluted, more biologically degraded state that is still evolving rapidly. Distinctive strata reflecting this change have already formed, and many of these planetary changes are effectively irreversible. A proposal for adding the Anthropocene to the Geological Time Scale is being prepared on this basis, but there is no guarantee that it will be accepted.”
Dr Alexander Farnsworth, Senior Research Associate in Geographical Sciences at the University of Bristol, said:
“This debate has been raging for well over a decade now indicating the complexities of defining a new geological period. A Plutonium signal has many advantages over other definitions, such as carbon or temperature excursions. It is available globally and in different environments where the signal is preserved at far greater concentrations than occurring at natural background levels for plutonium.
“In reality, humans have been influencing and fundamentally altering the Earth system (land, ocean, atmosphere) well before the 1950s. For instance, humans arguably started to become custodians of the Earth when large-scale agriculture became commonplace transforming the natural environment through a range of practices (removal of forests, burning, tilling of land, replacement of natural plant, animal and insect life, increased surface runoff of nutrients into riverine systems, etc.).
“However, the problem in finding a unique signal globally that will be preserved over geological timescales (10s to hundreds of millions of years) is very difficult. Would these early human civilisations where human populations grew rapidly through the adoption of agriculture be seen in the geological record in one, ten or even a hundred million years’ time? Potentially not.
“So the question becomes would a geologist in ten million years from now looking through a sedimentary or marine core see this plutonium ‘spike’? Certainly not. This is because plutonium, which is not a stable element, has a half-life (The time required for a radioactive substance to lose 50% of its radioactivity by decay) of anywhere between 87 – 24,065 years depending on the isotope. This decay process transforms plutonium into Uranium, which itself has a half-life of between 24–700 million years (depending on which Uranium-236/235 isotope is decaying) when it becomes lead. So the question remains whether the decay of Plutonium into Uranium (and ultimately Lead) will have a larger ‘spike’ in the geologic record compared to background levels. It is uncertain what such a Uranium/lead stratigraphic layer may look like globally on million-year timescales.
“Perhaps the more pertinent question is whether we should even need a new epoch defining the so-called Human-age? We are but a ripple in the river of gene flow through time. Is the purpose to detect the human impact on the natural earth system if we were to go extinct? If another advanced civilisation were to evolve in one hundred million years could they tell such a spike was due to a previous advanced civilisation or would they simply interpret it as an interesting natural excursion without any other evidence of our existence?
“The Silurian hypothesis may be pertinent to such a question, this states whether we would be able to detect whether such an advanced civilisation evolved in the geological record millions of years ago and whether you could attribute a carbon, radioactive elements or temperature ‘spike’ to it. So what is the purpose of defining an Anthropocene Epoch? To define our existence or to show how we have impacted the natural system for many hundreds of millions of years to come, or both?”
Declared interests
Prof Crispin Halsall has no conflicts of interest. His research on chemical pollutants and microplastics in the environment is funded through UKRI and EU sources.
Dr Alexander Farnsworth: “I have no pecuniary or other personal interest, direct or indirect, in any matter that raises or may raise a conflict with the content of the article.”
Prof Jan Zalasiewicz: “I’m a member, former Chair, of the Anthropocene Working Group, and now Chair of the Subcommission on Quaternary Stratigraphy – the first of the bodies that has to consider the Anthropocene proposal when it is submitted”.