In search of the place on the planet with the most scars caused by humans

This November 17, 2022, a select group of geologists, climatologists and paleontologists have begun the final process to choose the place on the planet that has the most scars caused by humans.

For a month they will have to analyze the nine sites that have best recorded the impact of our actions.

The main marker is the presence of radioactive material from nuclear bomb tests.

But they will also take into account the clear, continuous and countable footprint year after year in the sediment of other anthropogenic creations such as particles from burning gasoline, microplastics, technofossils, CO₂... In a month they should have the candidate to mark the beginning of the Anthropocene.

Although time and its passage is something continuous, humans like to establish it in seconds, days, years, decades, millennia... The geological time scale, referring to terrestrial history, is so large that other terms are used: cron , age, epoch, period, era and eon.

The eons and eras are the largest time ranges, spanning thousands or hundreds of millions of years.

In general, the separation between each of the major phases is marked by some cataclysm, such as the meteorite that wiped out the dinosaurs and marked the end of the Cretaceous period and the beginning of the Paleogene.

The lower lapses are usually marked by more cyclical events, such as epochs of ice age/deglaciation or the change in the magnetic polarity of the planet.

Now, the Earth is in the Holocene, an epoch that began about 11,000 years ago, with the end of the last great ice age.

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 geologic time divisions have their stratotype, a place where changes are best represented,” he says.

This group has spent years searching for and receiving proposals for stratotypes, for places that would bear the definitive mark of the Anthropocene.

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, places as humane as the Fresh Kills landfill (United States) arrived.

Opened in 1948, it was New York's garbage dump for more than half a century.

Nearly 30,000 tons arrived every day and it was closed in 2002, with the dumping of the remains of the Twin Towers demolished the previous year.

With a quantity of 150 million tons of garbage, 70 meters high and an area of ​​about 8 million meters², it could be the largest human creation ever created.

But it did not meet all the requirements and fell by the wayside.

“Plutonium-239 is the primary marker: it is artificial, its presence is global and we can follow it year by year”

Alejandro Cearreta, paleontologist at the University of the Basque Country

"The search for a stratitype is complicated," says Cearreta.

It should have the mark of a first change, the hallmark of one of the markers they have selected.

Chief among them is the presence of plutonium-239, the material used in the bomb that fell on Nagasaki and which fueled most nuclear tests and fuels today's atomic-charged missiles.

Plutonium-239 and other radioisotopes such as americium-241 or cesium-137, all man-made, are present in soils, peat bogs, lake and sea beds, trapped in ice columns or in rocks. tree rings.

“Plutonium-239 is the primary marker: it is artificial, its presence is global and we can follow it year by year”, adds the Basque scientist.

The nine sites that have made it to the final selection (referred to by the acronym GSSP) have recorded the presence of plutonium-239 since the 1950s.

Among them, as stated in an article recently published in the scientific journal

, there are two marine sediments, one in the Baltic Sea and the other in Beppu Bay, Japan.

Both made up of layers of carbon-rich clays and silt, they have captured several of the markers of the Anthropocene, such as spherical carboniferous particles that can only come from soot released by fossil fuels, microplastics or pesticides.

Also underwater are two reefs, one in the Gulf of Mexico and the other in Australia.

Corals can capture geochemical changes from year to year and over centuries.

Three other candidates are aquatic, but they are at the bottom of three lakes, one in Canada, the second in China and the third is a swamp from a US dam built in the late 19th century.

An ice core extracted from Antarctica and another from a peat bog in the Sudetenland, in Poland, close the list.

Geologist Colin Waters, Honorary Professor of Geography at the University of Leicester (UK), is also a member of the AWG.

Co-author of the work published in

remember that the ideal place to be considered a GSSP, a boundary between an epoch or period, should be "the best possible record of relevant marker events, such as plutonium precipitation."

In addition, "it must not have discontinuities in the accumulation of strata and the rate of its accumulation must generate sufficient thickness to be able to distinguish between time units," he details in an email.

Other essential characteristics are that the site is not altered by the action of biological organisms or human activities and that it allows dating from year to year.

Lastly, Waters completes, The candidate site "must have been intensively studied, be accessible for future research, and be protected from deterioration."

The plutonium from nuclear bombs has reached Antarctica.

One of the candidates to be the place with the clearest sign of the Anthropocene is the ice of the Palmer Archipelago, in the Antarctic Peninsula.getty

The latter left Tunelboka out in the previous selection phase.

Tunelboka is a cove in Getxo (Bizkaia) where there are recently formed rocks, no more than a century old.

The cemented sand includes waste materials from Bilbao's industrial past, such as iron ore slag or pieces of brick used in blast furnaces.

"The changes are evident there, with a 10-meter layer of technofossils," says Cearreta, who has studied them well.

“But the thickness of the gravel is so thick that it doesn't trap the primary tracer, plutonium, well.

Also, there is erosion from the sea and there are no guarantees that it will remain in the sediment for decades, centuries or thousands of years,” she adds.

Cearreta, Waters and the other AWG members have 30 days to select the finalist sites.

If one of them achieves 60% of the votes, then that will be the proposal as a place that will mark the beginning of the Anthropocene that they will make to the International Union of Geological Sciences (IUGS), on which this group depends. of work.

If not, they will continue voting until they choose one of those three.

The final decision could be in March, at an IUGS summit in Berlin.

The votes are secret and confidential and they have to decide something else, besides the site with the biggest brands of the Anthropocene.

They have to determine if all the change that is taking place is great enough to replace the Holocene.

"We have to vote on the scale," recalls Cearreta.

The Holocene is an epoch, with its recently named subdivisions (age or chron) (Greenlandian, North Grippian, and Megalayan).

“It could be decided that it was a subdivision of the Holocene, an age, but the scale of the changes that humans are making to the planet is unprecedented.

We have seen other extinctions and geochemical changes, but the speed, quantity and intensity of the current changes are unparalleled”, adds the scientist from the University of the Basque Country.

Which is not going to happen, Waters recalls in his email,

it is to classify the Anthropocene as a new period (now we are in the Quaternary) and even less 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 then, Cearreta ends, "it would no longer make sense to call it the Anthropocene, nor would there be anyone to name it."

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