Where exactly and when did the Anthropocene begin? Scientists are attempting to answer this epochal question in the coming months, choosing a place and time to portray the moment when humanity became a “geological superpower”, overcoming the natural processes that have ruled the Earth for billions of years.
They could decide the beginning is marked with a bang, thanks to the plutonium isotopes rapidly fired around the planet by the hydrogen bomb tests that began in late 1952, or the rain of soot particles from the boom of fossil fuel power plants after World War II.
Or they can choose the post-war explosion in the use of artificial fertilizers and its profound impact on the Earth’s natural nitrogen cycle. Microplastics, chicken bones, and pesticide residues can also be among the eclectic signs used to reinforce the definition of the Anthropocene. Other possible signs include lake beds in the US and China, Australian corals, a Polish peat bog, black sediments under the Baltic, and even human remains accumulated near Vienna.
An international team of nearly 40 scientists, commissioned by the official custodians of the geological timescale, must select a site where layered sediments show a clear transition from the previous epoch to the new one. The team has compiled a shortlist of 12 sites that have just kicked off their voting streak – but there can only be one winner. Humanity has undoubtedly changed the Earth far beyond the stability of the Holocene, the 11,700-year period in which all civilization arose and which will end with the announcement of the Anthropocene. The atmosphere, lakes and oceans, and the living world have been transformed by greenhouse gas emissions, pollution, and the destruction of wildlife and ecosystems. Humans also now have a greater influence on shaping the Earth’s surface than natural processes, moving about 24 times more material than rivers do.
Scientists say defining the Anthropocene is critical because it brings together all human influences on the world, thus providing a platform for holistic understanding and hopefully corrective action. From a scientific point of view, a precise definition is essential to create a clear basis for the debate.
The first stage of voting is already underway. The site will need to exhibit ‘specific physical properties in layers or layers of sediment that reflect the effects of recent human population growth; unprecedented industrialization and globalization; and changes imposed on the landscape, climate and biosphere,” according to a recent article in the journal Science by Professor Colin Waters of Leicester University and Dr Simon Turner of University College London, chair and secretary of the Anthropocene Working Group (AWG), respectively.
But creating a new unit of time is a big decision in geological circles, and in parallel, the AWG has a bigger job to do – to convince geologists that a new epoch is justified at all.
Both tasks come down to identifying clear markers of change, and hundreds of scientists are doing just that. Broad indicators of anthropogenic transformation include rising levels of carbon dioxide in the atmosphere, recorded in trapped air bubbles in ice cores, and massive shifts in populations and species locations, with the exponential growth and spread of human and livestock numbers similar to how wild animals plunge into and disappear.
But other markers offer the “golden leap” needed to precisely define and allow layers to register a sharp, clear growth. Chief among these is the distinctive imprint of radioactive isotopes, particularly plutonium, produced in Cold War hydrogen bomb tests, the first of which was conducted by the United States on November 1, 1952, at Eniwetok Atoll in the Marshall Islands in the Pacific.
Dozens of ground tests soon followed, some even rocketing into the stratosphere. The effects of the tests were rapid and global, orbiting the planet in about 18 months until atmospheric testing was banned in 1962.
“They were testing their new arsenal a lot for a short period of time,” Turner said. “That’s why you have this very unique, timed, global tag that’s so useful to our work.”
Another useful tracer is small spheroidal carbon particles (SCPs), a type of hard fly ash produced solely by burning coal or heavy oil at high temperature. “They took off with the surge in thermoelectric power plants after World War II,” Turner said. “They are good at traveling on a continental scale and can be found all over the world because many continents have produced them.” Work done for AWG revealed SCPs in Antarctic ice cores for the first time.
Scientists have found that plastic pollution is also a marker of the Anthropocene. “The 1950s is when you start to see most of the polymers that were known to be invented and started showing up in products,” Waters said, with nylon essentially replacing silk during World War II, for example.
Plastic waste can now be found from the top of Mount Everest to the deepest ocean trench, giving a global signal. Other scientists discovered in 2019 that plastic is deposited in layers and suggested that the Stone and Iron Ages were followed by the Plastic Age. However, the sharpest increase in plastic pollution occurs several decades after plutonium isotopes from H-bomb testing, although both have the advantage of never having appeared in the geologic record before.
Some scientists have suggested that broiler chicken bones are a marker of the Anthropocene, with their production rapidly increasing since World War II. In addition, agricultural breeding means that their skeletons and genetics are distinctly different from their wild ancestors.
“Chickens are by far the largest population of birds on the planet right now,” Waters said. “But also two-thirds of the mass of large mammals on the planet are domesticated species – cows, sheep, pigs, etc. This is obviously a big change in species populations, especially considering the reduction in the number of natural species.” The WWF estimates that the size of the wild animal population will decrease by an average of 70%. These biological changes are large, but more gradual than other markers, Waters said.
The researchers say that invasive species introduced by humans to new regions could also be markers. The inadvertent import of alien species into the ballast water of ships arriving in San Francisco from Asia changed the bay. “There was a point where 98% by weight of all animal species in the bay were actually invasive,” Waters said. Pollen from introduced plant species, such as trees used in commercial forestry, can also record changes.
Chemical and metallic pollutants are also showing up in the sediments, Turner said: “The Green Revolution relied on artificial fertilizers and pesticides, so you can see it in the sediment cores. A whole cocktail of industrial chemicals exploded after the war.” Whether the chemicals persist in the environment long enough to be markers of the Anthropocene remains to be determined.
The 12 potential locations for the site that will define a new era contain some markers, but they vary widely. “Since the Anthropocene has not been formally accepted, we are still trying to prove to people that it is not something localized, but something that can be found and correlated in many different environments,” Waters said.
“They all illustrate very well this dramatic transformation of the Anthropocene. But the places that really stand out are the ones where you can actually see the annual resolution of the layers,” Turner said, including some lakes, corals and polar glaciers. “It’s quite astounding that these pages detail planetary changes in yearly resolutions.”
They all have advantages and disadvantages. The 32-meter Palmer Ice Core from the Antarctic Peninsula is the longest record of the Anthropocene, but its remote location means that the track of some markers is often faint. With the beginning of the Anthropocene, the sediments of the Baltic Sea change color from pale to black. This is caused by pollution-driven algae blooms sucking all the oxygen out of the water. But the settlements do not have annual laminates. An archaeological site in the center of Vienna gives a 200-year-old record, dated by artifacts, but has gaps in the record due to reconstruction.
The choice of the site, and thus the official time and place of the dawn of the Anthropocene, is up to the 23 voting members of the AWG, but then it will have to be approved by the Subcommittee on the Stratigraphy Commission and finally ratified by the International Union of Geological Sciences. There is also a deadline: the international geological congress in South Korea in 2024, when the mandate of the AWG expires. “It was pretty much said we had until then to do it,” said Waters.
Professor Naomi Oreskes of Harvard University and a non-voting member of the AWG said: “As geologists, we’ve been taught to think humans are insignificant. It used to be true, but not anymore. The evidence collected by the AWG shows beyond doubt that the human footprint is now visible in rocks and sediments. The Anthropocene is primarily a scientific concept, but it also highlights the cultural, political and economic implications of our actions.”
UCL Professor Mark Maslin, who co-authored The Human Planet with Prof. Simon Lewis, he said: “I think the Anthropocene is a critical philosophical term because it allows you to think about what impact we have and what impact we want to have. in the future.”
Maslin and Lewis had previously proposed 1610 as the beginning of the Anthropocene, representing the immense and deadly impact that European colonists had on America and by extension the world. But Maslin said agreeing on a definition is more important than placing it exactly.
“So far we’ve talked about things like climate change, the biodiversity crisis, the pollution crisis as separate things,” he said. “The key concept of the Anthropocene is to put it all together and say that humans have a huge impact on the Earth, we are the new geological superpower. This holistic approach then allows you to say, “What are we going to do about it?”