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Anthropocene: Searching for the Site That Best Depicts Man’s Impact on the Planet | Science & Technology

On Thursday, November 17, 2022, a select group of geologists, climatologists and paleontologists began the final process of choosing the place on the planet that best reflects human-induced changes on the Earth. For the next month, they will analyze the nine sites that have the best data on the impact of our actions. The main indicator of that impact is the presence of radioactive material from nuclear tests. But they will also consider the clear, continuous, and countable footprint left year after year in the sediment of other anthropogenic creations, including particles from burning gasoline, microplasticstechnofossils, CO₂, etc. The scientists must have a candidate for a firm date for the beginning of the Anthropocene – a new geological era that marks the beginning of a significant human impact on the planet – within a month.

Although time passes constantly, man divides it into seconds, days, years, decades, millennia… The geological time scale, which refers to the history of the earth, is so large that other terms are used: chron, age , epoch , period, epoch and eon. Centuries and eras are the greatest temporal units; they span hundreds of millions or billions of years. Generally, the separation between each of the main phases is interrupted by a catastrophe, such as the meteorite that wiped out the dinosaurs, marking the end of the Cretaceous and the beginning of the Paleogene. Shorter time periods are usually characterized by more cyclical events, such as glaciation/deglaciation or changes in the planet’s magnetic polarity. Earth is currently in the Holocene, an epoch that began about 11,000 years ago with the end of the last major ice age. This group of scientists, who Working Group Anthropocene (AWG)discusses whether the Holocene has ended and humans have begun their own era, the Anthropocene, and where that change is most apparent.

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Alejandro Cearreta, paleontologist from the University of the Basque Country, an expert on the human footprint and environmental change, is one of the 23 members of the AWG. “All divisions of geological time have their [own] stratotype, a place where changes are best reflected,” he says. For years, the group has been seeking and receiving proposals for stratotypes – places that would definitively mark the beginning of the Anthropocene. Man-made sites, such as the Fresh Kills landfill in the United States, have reached the semi-final selection stage. Opened in 1948, the site served as New York’s garbage dump for more than half a century. Nearly 30,000 tons of rubbish came in every day until it closed in 2002, following the removal of the rubble from the Twin Towers that collapsed in a terrorist attack last year. The Fresh Kills landfill is 70 meters high and covers an area of ​​about eight million square meters; it contains 150 million tons of waste, which could be the greatest human creation ever made. But the landfill did not meet all the requirements to be considered a stratotype and was rejected.

Plutonium from nuclear bombs has reached Antarctica. The ice on the Palmer Archipelago, located on the Antarctic Peninsula, is a candidate for the site with the clearest signs of the onset of the Anthropocene. getty

“Searching for a stratotype is complicated,” says Cearreta. To qualify, it must indicate a first change, which is indicative of one of the markers the scientists selected. The main marker is the presence of plutonium-239, the material used in the bomb dropped on Nagasaki, which also led to most nuclear tests and powers today’s atom-loaded rockets. Plutonium-239 and other radioisotopes, such as americium-241 and caesium-137, which are all man-made, are present in soils, peat bogs, lakes and seabeds, as well as trapped in ice columns and tree rings. “Plutonium-239 is the primary marker [because] it is artificial, it is present worldwide and we can track it from year to year,” explains the Basque scientist.

The nine sites (called Global Boundary Stratotype Sections and Points and designated by the acronym GSSP) that made it to the final round of the selection process have recorded the presence of plutonium-239 since the 1950s. As reported in an article recently published in the scientific magazine Science, the options include two marine sediments, one in the Baltic Sea and the other in Japan’s Beppu Bay. Both are made up of layers of carbon-rich clay and silt, and have captured distinct features of the Anthropocene, such as spherical carbon particles that could only have come from soot released by fossil fuels, microplastics, or pesticides. Two reefs, one in the Gulf of Mexico and the other in Australia, are also in the running. Coral reefs can record geochemical changes from year to year and over centuries. Three other candidates are also aquatic, but they are at the bottom of three lakes; the first is in Canada, the second in China, and the third in the United States; the latter is the reservoir of an American dam built in the late 19th century. Ice cores, one extracted from Antarctica and the other from a peat bog in Poland, complete the list of candidates.

Geologist Colin Waters, Honorary Professor of Geography at the University of Leicester (UK), is also a member of the AWG and co-author of the recently published paper in Science. Waters explains that the ideal GSSP, which is a boundary between an era or period, should be “the best possible record of relevant marker events, such as plutonium deposition.” In addition, the GSSP “should not have discontinuities in the accumulation of layers, and the rate of their accumulation must generate sufficient thickness to distinguish between units of time,” he says in an email. The site must not be altered by the actions of biological organisms or human activities, and it must allow year-to-year dating. Finally, Waters adds, the candidate site should be “intensively studied, accessible for future research, and protected from degradation.”

Cearreta, Waters and other AWG members have 30 days to select the three finalists. If a site wins 60% of the vote, it will be the AWG’s proposal to the International Union of Geological Sciences (IUGS; the organization to which the working group belongs) to mark the beginning of the Anthropocene. If not, the members will continue to vote until they choose one of the three. The final decision could come in March at the IUGS summit in Berlin.

The votes are secret and confidential. In addition to selecting the site with the clearest record of the Anthropocenevoters must also determine whether the changes taking place are large enough to replace the Holocene. “We have to vote for the scales,” says Cearreta. The Holocene is an epoch, and recently its subdivisions (age or chron) have been named (Greenlandic, Norgripian and Megalayian). “[The AWG] might conclude that it is a subdivision of the Holocene [epoch]…but the magnitude of the changes we humans are making on the planet is unprecedented. We have seen other extinctions and geochemical changes, but the speed, quantity and intensity of the current changes are unparalleled,” added Cearreta.

Waters notes in his email that the Anthropocene will not be classified as a new period (we are now in the Quaternary), let alone a new epoch (the current one is the Cenozoic). Such a change would require catastrophe, such as the extinction of the human race. But by the time that happens, Cearreta concludes, “there would be no point in calling it the Anthropocene, and there would be no one to name it.”

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