Scientists say they found a place that marks a new chapter in Earth’s history

() — Scientists have identified the geological site that they believe best reflects a proposed new epoch called the Anthropocene, taking a big step toward changing the official timeline of Earth’s history.

The term Anthropocene, first proposed in 2000 to reflect the extent to which human activity has altered the world, has become a buzzword in academic circles across many fields of study.

“When 8 billion people have an impact on the planet, there will inevitably be repercussions,” says Colin Waters, Honorary Professor in the School of Geography, Geology and the Environment at the University of Leicester and Chairman of the Anthropocene Working Group. (AWG).

“We have moved into this new state of the Earth and that should be defined by a new geological epoch,” Waters added.

The AWG, a group currently made up of 35 geologists, has been working since 2009 to make the Anthropocene part of Earth’s official chronology. The group determined in 2016 that the Anthropocene epoch began around 1950, the beginning of the era of nuclear weapons testing, the geochemical traces of which can be found around the world. Since then, the researchers have considered 12 locations that could provide the key piece of evidence needed to support their proposal, nine of which were put to a vote.

This Tuesday, scientists announced the geological site that best captures the geological impact of the Anthropocene, according to their research: Crawford Lake, in Ontario, Canada.

However, not everyone agrees that the Anthropocene is a geological reality, or that researchers have enough evidence to formally declare it a new epoch.

split time deep

The geologic time scale is the official framework for understanding Earth’s 4.5 billion-year history. Geologists divide the history of our planet into eons, eras, periods, epochs, and ages, with an eon being the longest and an age the shortest.

For example, we currently live in the Megalayense Era. It is part of the Holocene Epoch, which began at the end of the last ice age 11,700 years ago, when the polar ice caps and glaciers began to recede. The Holocene is part of the Quaternary Period, the most recent division of the Cenozoic Era, which in turn is part of the Phanerozoic Eon, which spans from 539 million years ago to the present.

This is a global stratotype section, or golden spike, in the Flinders Ranges of South Australia that marks the beginning of the Ediacaran Period, which began 635 million years ago. Credit: James St. John/Flickr

These geologic chapters are often named after the place where they were first studied. The Jurassic takes its name from the fossil-rich rocks of the French Jura Mountains, while the Cambrian takes its name from the Roman name for Wales.

Andrew Knoll, the Fisher Professor of Natural History at Harvard University, called the scale “profoundly useful” for his work as a paleontologist.

“When I say ‘Cambrian,’ this conveys not just the time between 539 and 485 million years ago, but a wealth of information about biota, environments, tectonics, paleogeography, and more,” Knoll said. “(It’s) a bit like saying the Middle Ages, or the Renaissance.”

If approved, the Anthropocene would be the third epoch of the Quaternary. It would also mean that the Holocene Epoch was especially short, other epochs have lasted several million years.

Each division of the official chronology is also represented by a single geologic location, known as a Global Frontier Stratotype Point and Section (GSSP), which best captures what is novel or unique about a particular chapter of the history of the Land.

Each point is usually marked with a “golden spike”, often embedded in the bedrock layer, although the location may be a stalagmite or ice core.

Birthplace of the Anthropocene

For the Anthropocene, the proposed location for the golden spike is sediment mined from the Crawford Lake bed, which reveals the geochemical fingerprints of nuclear bomb tests, specifically of plutonium, a radioactive element widely detected around the world in coral reefs. , ice cores and peat bogs.

Annual sediment samples from Crawford Lake have revealed geochemical traces of nuclear bomb tests, the researchers confirmed. Credit: Courtesy of the University of Southampton

Crawford Lake emerged as the winner after the AWG voted for all nine candidate sites in three rounds. The other possible sites were a peat bog in the Polish Sudetenland, Lake Searsville in California, a strip of seafloor in the Baltic Sea, a bay in Japan, a water-filled volcanic crater in China, an ice core drilled on the Antarctic Peninsula. and two coral reefs, one in Australia and one in the Gulf of Mexico.

According to Waters, it was very difficult to choose between the different sites and the votes were close, but he believes that Crawford Lake won because the proposed geochemical starting point of the sediment-associated Anthropocene is particularly accurate.

The lake is not large, covering 2.4 hectares, but it is exceptionally deep, nearly 24 meters, and the sediment at the bottom can be broken down into annual layers to sample geochemical markers of human activity. This analysis allows scientists to observe the changes at a yearly resolution, explained Francine McCarthy, a professor of Earth sciences at Brock University in Canada, who has studied the lake.

“The shape (of the lake) restricts the mixing of the water column, so that the bottom waters do not mix with those on the surface. The bottom of the lake is completely isolated from the rest of the planet, except for what sinks gently to the bottom,” he explained.

Andrew Cundy, Professor and Chair of Environmental Radiochemistry at the University of Southampton and member of the AWG, said: “The presence of plutonium gives us a clear indicator of when humanity became such a dominant force that it was able to leave a ‘fingerprint’ global unique on our planet”.

However, the selection of Crawford Lake is not the final decision on the recognition of the Anthropocene as an official geological temporal unit.

The AWG will present a proposal to make the Anthropocene official to the Quaternary Stratigraphy Subcommittee later this summer. If the members of the subcommission agree with a 60% majority, the proposal will go to the International Commission on Stratigraphy, which will also have to vote and agree with a 60% majority for the proposal to go forward for ratification. . Both organizations are part of the International Union of Geological Sciences, which represents more than a million geoscientists from around the world.

A final decision is expected at the 37th International Geological Congress to be held in Busan, South Korea, in August 2024.

The great anthropocene debate

Some experts don’t think the Anthropocene is epoch-defining.

Stan Finney, secretary general of the International Union of Geological Sciences and professor in the Department of Geological Sciences at California State University, Long Beach, said the Anthropocene stratigraphic record is relatively minimal, barely a human lifetime, since the point of The proposed departure is around 1950.

The beginning of the Anthropocene could be defined in many ways, including the Industrial Revolution, which would result in a much longer interval than currently proposed, he noted.

The alpha spectrometry result displayed on the screen indicates the presence of plutonium in a drill sample from Crawford Lake. Credit: courtesy of the University of Southampton

“There is no doubt that human beings have greatly influenced the terrestrial system and that today we are facing unbelievable consequences. But it is a phenomenon that comes from afar,” he says.

He also believes that the drive to officially recognize the Anthropocene may be more political than geological. The term was coined in the year 2000 not by a geologist, but by atmospheric chemist and Nobel Prize winner Paul Crutzen, apparently in a impromptu speech at a conference.

According to Finney, it is more accurate to describe humanity’s profound impact on Earth as an ongoing geological event than as a formal epoch with a precise global start date. It is also possible, he said, that stratigraphers decide that the Anthropocene is not epoch-level, but could be the fourth Holocene age, the much less attractive Crawfordian Age.

Others object to the term Anthropocene because it implicates all of humanity in activity that has irrevocably altered the planet. Some researchers claim that the changes are the work of a powerful and elitist minority and that the epoch would be better called “capitalocene“.

Waters believes the AWG has a strong case to formalize the Anthropocene, but said naming a new geological epoch “is a very conservative process,” so there are no guarantees the proposal will succeed.

In addition to Crawford Lake, the AWG also has to choose two secondary sites before submitting a proposal.

“We’ve been very careful in our search for the right (reservoirs), but you might say at the end of the day ‘We’re not impressed with the evidence you provided to show that the Anthropocene is justifiably a new epoch in geologic time,'” Waters said.

“They may also support the idea that there is a stage here and that the Crawford site represents a new stage of the Holocene, but they are not willing to accept that the Anthropocene is significant change beyond the curve of change that we see within the Holocene. “, he added.

Andrew Mathews, professor of Anthropology at the University of California at Santa Cruz, said that the term Anthropocene has already demonstrated its importance, opening conversations between the natural sciences, the social sciences and the humanities. Therefore, the exact geological place where the proposed epoch was born may not ultimately matter much.

“It has been established that human societies are having a geological impact on the world and on Earth systems. And that part is useful,” he said. “He’s basically saying, ‘Look, we’re on it. We changed the world and we have to keep thinking about it,'” she added.