This calm Canadian lake could be the marker of the new Anthropocene epoch

The official marker of the early Anthropocene is a small, deep Canadian lake whose sediments accumulated chemical remnants of radioactive fallout from nuclear bombs and other forms of environmental degradation. This was proposed by an international team of researchers. who spent 14 years debating when and how mankind began to alter the planet.

He Working Group on the Anthropocene announced the appointment of Lake Crawford this week at an International Commission on Stratigraphy (ICS) conference held in Lille, France. Three geological organizations must approve the election for it to become the official marker.

Some geologists have long argued that we live in the Anthropocene, a new geological era in which the human activity has become the dominant influence on the planet’s climate and environment, especially since the middle of the last century.

Year after year, the particles sink to the bottom of the lake and form layers of sediment that record environmental conditions much like tree rings.

The concept has important implications for the way we view our impact on the planet. But there is disagreement in the scientific community about when the Anthropocene began, how it was evidenced, and whether human influence was substantial enough to constitute a new geological age, which normally spans millions of years. To help answer these questions, the ICS created the Anthropocene Working Group.

The ‘golden nail’ of the early Anthropocene

If the proposal is approved, a core of Crawford Lake sediments would become the ‘golden peak’, marking the beginning of the Anthropocene. Year after year, the particles are deposited in the lake and end up at its bottom, forming sediment layers that record environmental conditions in a similar way to tree rings.

Among the incorporated contaminants are particles of fly ash – leftovers from the burning of fossil fuels – and traces of radioactive plutonium, from atmospheric tests with nuclear bombs.

Embedded contaminants include particulate fly ash from burning fossil fuels and radioactive plutonium debris from nuclear bomb tests.

“We have the main Anthropocene markers – at Crawford Lake they line up perfectly,” he says. Francine McCarthymicropaleontologist at Brock University in St Catharines (Canada), who leads the team studying the lake.

The team collected samples from various environments around the world, from coral reefs to ice sheets, which were analyzed at the GAU-Radioanalytical Laboratories at the University of Southampton (UK). There, the researchers processed the samples to detect a key marker of human influence on the environment: presence of plutonium.

The team collected samples from various environments around the world, from coral reefs to ice sheets.

Andre CundyProfessor of Environmental Radiochemistry at the University of Southampton and member of the Anthropocene Working Group, explains: “The presence of plutonium offers us a crude indicator of when humanity became such a dominant force that it was able to leave a ‘fingerprint” only global on our planet”.

Chemical digestion of Crawford Lake samples to extract plutonium. / University of Southampton

hydrogen bomb tests

“In nature, plutonium is only present in trace amounts. But in the early 1950s, when the first hydrogen bomb tests were carried out, there was a unprecedented rise in plutonium levels in samples from around the world. From the mid-1960s, when the Nuclear Test Ban Treaty came into force, there was a decline,” explains Cundy.

The presence of plutonium offers a crude indicator of when humanity became such a dominant force that it was able to leave a unique global ‘fingerprint’ on the planet.

Andrew Cundy (University of Southampton)

The Great Acceleration

Other geological indicators of human activity are high ash levels from coal plantsthe high concentrations of heavy metalssuch as lead, and the presence of plastic fibers and fragments. All this coincides with the big acceleration (or Anthropocene), a dramatic increase in human activities, from transportation to energy use, that began in the mid-20th century and continues today.

Of the hundreds of samples analysed, the Crawford Lake core was proposed as the only point on the global frontier (or ‘golden nail’) stratotype, along with other secondary deposits that show similar high-resolution human impact records. The evidence from the deposits will now be presented to the ICS, which next year will decide whether to ratify the Anthropocene as a new geological epoch.

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