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A humble lake in a Canadian suburb may soon become the symbolic starting point for a radically new chapter in official Earth history: the Anthropocene, or Age of Man.
A group of scientists said Tuesday that the best evidence of humanity’s overwhelming impact on the planet can be found at Crawford Lake in Milton, Ontario. The lake’s finely stratified sediments contain a thousand-year record of environmental history, culminating in an explosion of man-made disturbances around the mid-20th century. That’s when human activity — from nuclear weapons testing and the burning of fossil fuels to deforestation and global trade — began leaving an indelible mark on the Earth’s geological record, according to scientists.
The announcement marks a crucial step in a year-long attempt to determine if humans have altered the planet enough to usher in a new epoch in geologic time. Since 2009, an obscure scientific body called the Anthropocene Working Group has been collecting evidence that Earth’s chemistry and climate are radically different from conditions of the past few thousand years. The final requirement was to identify a “golden thorn” – a spot in the geological record that perfectly preserved the dangerous transformation wrought by humans.
Crawford Lake shows that “all the different components of the Earth system and the way they interact with each other are fundamentally different than they used to be,” said Francine McCarthy, a professor of geosciences at Brock University in Ontario, who led the research at the lake . “We felt this was the best place to illustrate this existential problem.”
At the International Congress of Stratigraphy – a semi-regular meeting of researchers studying the phases of the Earth’s past – working group members recommended establishing the Anthropocene as a new epoch from 1950, with Crawford Lake as the golden apex.
Read more: Dig in the sediments of Crawford Lake to see how humans have changed the planet
Before the Anthropocene can be added to Earth’s official 4.6-billion-year timeline, it must withstand scrutiny by the broader geological community. In the coming months, the proposal will be presented to the Sub-Commission on Quaternary Stratigraphy, which is responsible for subdividing the history of the last 2.4 million years. Then the larger International Commission on Stratigraphy will vote. If these bureaucratic hurdles can be overcome, the proposal will be ratified at next year’s International Geological Congress in South Korea.
Crawford Lake was selected from twelve candidates for a gold pinnacle around the world, including the ice of Antarctica, two remote coral reefs, a mountaintop peat bog and a polluted bay in California. All contained evidence of the same simultaneous increase in human pollution around 1950 — specifically, a sudden surge in radioactive plutonium from nuclear weapons tests, which will serve as a key marker of the Anthropocene.
“There is a very precise geochemical boundary that is present across the planet and in all environments,” said Colin Waters, a geologist at the University of Leicester and chair of the Anthropocene Working Group.
But after months of deliberation, the 22 voting members of the working group—including McCarthy and Waters—concluded that Crawford Lake captures the evidence for the Anthropocene better than anywhere else. In addition to nuclear fallout, the lake also shows signs of industrial pollution, species extinction, and global climate change. Tiny black particles called fly ash – a by-product of burning fossil fuels – are dispersed in the sediments. Changes in the type of tree pollen buried show how the surrounding forest responded to steadily rising temperatures.
“It’s not just about climate change. It’s not just about the loss of biodiversity. It’s not just the sediments that humans move. It’s all together,” said Jürgen Renn, director of the Max Planck Institute for the History of Science in Berlin, which supported the research of the working group. “We need to approach it as a multi-connected phenomenon. And we must strive to understand it and adapt our societies accordingly.”
However, not all scientists are convinced that the Anthropocene belongs to the geological time scale.
All other epochs were named millennia after their occurrence. They are not defined by instrumental data and witness accounts, but by the records of environmental change stored in rocks, tree rings, sediments, and ice. A Tunisian rock face with evidence of an ancient meteor impact signals the end of the age of dinosaurs. The beginning of the Holocene – the epoch spanning the last 11,700 years – is marked by trapped hydrogen molecules in the ancient Greenland ice sheet.
“I’m not sure something that lasts only a few decades can count as a new geological age,” said archaeologist Sturt Manning, who directs Cornell University’s Tree Ring Laboratory. “You can’t really define your own time.”
Other researchers fear that a strict geological definition of the Anthropocene could have implications far beyond the hidden halls of science.
“The stories we tell aren’t just scientifically neutral stories,” said Andrew Bauer, an anthropologist at Stanford University who studies human interactions with the environment. “There are potential political ramifications.”
For example, identifying the mid-20th century as the starting point of the Anthropocene could lead to human influences before that date being downplayed. On the other hand, the term “Anthropocene” implies that all humans are equally responsible for the transformation of the planet – when research shows that the world’s wealthiest people and nations are responsible for the bulk of carbon emissions and other environmental damage.
“No one I know who has been critical of the Anthropocene would want to deny human impact on the Earth system,” Bauer said. He is among a group of scientists who have proposed defining the concept as a geological “event” rather than an epoch — a more flexible term that could encompass all of the nuanced ways humans have changed and of nature over the millennia were formed.
“The concept of an unprecedented geological transformation that has taken place in the last 70 years is a big statement,” said Simon Turner, environmental scientist at University College London and secretary of the Anthropocene Working Group.
But the evidence from Crawford Lake and the other sites studied by the working group is “indisputable,” he said — and growing stronger every year. As long as people continue to wreak havoc on the environment, the consequences of those choices will remain ingrained in the earth, he said.
But even if the Anthropocene is never officially included on Earth’s geologic timescale, McCarthy hopes the findings from Crawford Lake will prompt people to confront climate change, biodiversity loss, and other environmental changes.
“It will at least have been an attempt to quantify and communicate how quickly and how irrevocably our actions can change big things that people didn’t think could change,” McCarthy said.
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