Anthropocene: in search of the site that best represents the impact of human beings on the planet | Science and 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 represents human-caused changes to Earth. For the next month, they will look at the nine sites that have the best records of the impact of our actions. The main indicator of this impact is the presence of radioactive material from nuclear tests. But they will also take into account the clear, continuous, and countable footprint year after year left in the sediment by other anthropogenic creations, including particles of burned gasoline, microplasticstechnofossils, CO₂, etc. Scientists must have a candidate for a fixed date for the beginning of the anthropocene – a new geological epoch ushering in a significant human impact on the planet – within a month.

Although time passes constantly, human beings break it down 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: cron , age, time. , period, era and eon. The eons and the eras are the largest temporal units; They span hundreds of millions or billions of years. In general, the separation between each of the main phases is marked by a cataclysm, such as the meteorite that wiped out the dinosaurs, marking the end of the Cretaceous period and the beginning of the Paleogene. Shorter time periods are often marked by more cyclical events, such as ice ages/deglaciation or changes in the planet’s magnetic polarity. The Earth is currently in the Holocene, a time that began about 11,000 years ago with the end of the last great Ice Age. This group of scientists, who form the Anthropocene Working Group (AWG)is discussing whether the Holocene has ended and humans have begun their own epoch, the Anthropocene, and where that change is most evident.

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

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

“Looking for a stratotype is complicated,” says Cearreta. To qualify, you must indicate a first change, which is an indication of one of the markers the scientists have selected. The main marker is the presence of plutonium-239, the material used in the bomb dropped on Nagasaki, which has also fueled most nuclear tests and fuels today’s atomic missiles. Plutonium-239 and other radioisotopes, such as americium-241 and cesium-137, 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, its presence is global and we can follow it year by year”, explains the Basque scientist.

The nine sites (called Global Boundary Stratotype Sections and Points and referred to by the acronym GSSP) that have reached the final round of the selection process have recorded the presence of plutonium-239 since the 1950s. As reported in a paper published recently in the scientific newspaper Sciences, the options include two marine sediments, one in the Baltic Sea and the other in Japan’s Beppu Bay. Both consist of layers of carbon-rich clays and silt and have captured several of the markers of the Anthropocene, such as spherical carbonaceous particles that can only come from soot released by fossil fuels, microplastics, or pesticides. Two reefs, one in the Gulf of Mexico and one in Australia, are also in the running. Coral reefs can capture geochemical changes from year to year and over centuries. Three other candidates are also aquatic, but are located at the bottom of three lakes; the first is in Canada, the second is in China, and the third is in the United States; the latter is the reservoir of an American dam built in the late 19th century. Ice cores, one taken 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 Sciences. Waters explains that the ideal GSSP, which is a boundary between an epoch or a period, should be “the best possible record of relevant marker events, such as plutonium precipitation.” In addition, the GSSP “should not have discontinuities in the accumulation of strata, and the rate of their accumulation must generate enough thickness to be able to distinguish between units of time,” he says in an email. The site must not be altered by the action of biological organisms or human activities, and must allow year-by-year dating. Finally, Waters adds, the candidate site “must have been intensively studied, accessible for future research, and protected from deterioration.”

Cearreta, Waters and other GTE members have 30 days to select the three finalists. If a site wins 60% of the vote, then 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. Otherwise, members will continue voting until they choose one of the three. The final decision could come in March at the IUGS summit in Berlin.

Votes are secret and confidential. In addition to selecting the site with the clearest record of the Anthropocene, voters must also determine whether the changes that are occurring are large enough to warrant Holocene replacement. “We have to vote in the balance,” says Cearreta. The Holocene is an epoch, and its subdivisions (age or chron) were recently named (Greenlandian, Norgripian, and Megalayian). “[The AWG] might decide it’s a subdivision of the Holocene [epoch]…but the scale of the changes humans are making to the planet is unprecedented. We have seen other extinctions and geochemical changes, but the speed, amount and intensity of the current changes are unparalleled”, adds Cearreta.

Waters points out in his email that the Anthropocene will not be classified as a new period (now we are in the Quaternary), much less as a new era (the current one is the Cenozoic). Such a change would require a cataclysm, like the extinction of the human race. But by the time that happens, Cearreta concludes, “it would no longer make sense to call it the Anthropocene, and there would be no one around to name it.”

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