Updated Jul 11, 2023 - Science

Scientists say Canadian lake marks start of the Anthropocene

Sediment core from Crawford Lake

A Crawford Lake core sample is pictured at the Royal Ontario Museum in Toronto earlier this year. Photo: Lance McMillan/Toronto Star via Getty Images

Earth's 4.5 billion-year history is divided into geological epochs that each typically span millions of years. On Tuesday, scientists announced that sediment at the bottom of a lake in Ontario, Canada, contains key indicators that the world has entered a new epoch called the Anthropocene.

The big picture: These researchers say humans, rather than a natural phenomenon like an asteroid strike, pushed the planet into this phase — one in which Earth is being rapidly transformed.

  • "[W]e are living in a new geological period, one in which the scale and power of human activities match or even exceed the scale and power of natural processes," Naomi Oreskes, a professor of the history of science at Harvard University, tells Axios via email.

Driving the news: A working group of the International Commission on Stratigraphy announced sediment from the bottom of Crawford Lake in the suburbs of Toronto contains markers of "human-caused planetary change" and "the socio-economic dynamics and violent histories that continue to drive the Anthropocene."

  • But in defining a new epoch, the researchers are primarily focused on finding a geologic record of changes that occurred globally.
  • Starting in the 1950s, the sediment record contains artificial radionuclides from nuclear weapons testing that spread radioactive elements around the planet.
  • Markers of industrialization and globalization — nitrogen and mercury released from burning fossil fuels, microplastics pollution, nitrogen from fertilizers and other changes — also spiked at different places across the globe in the mid-20th century.

How it works: A key element for designating an epoch is a "golden spike" — a place on the planet where evidence of the start of a global change is found etched into rock, sediment or ice.

  • Since 2019, teams of scientists have been studying sites around the world — from the lake in the Toronto suburbs and a coral reef in Australia to peatland in Poland and the floor of the Baltic Sea — in search of a location that best captures a permanent record of the alterations humans have made to planet as a whole.
  • At Crawford Lake, soot, logging debris, pollen and other particles that carry fingerprints of human activities drop to the lake bottom.
  • Their age can be determined by a layer of calcite that forms on top of sediment each year during the summer, the Washington Post's Sarah Kaplan writes, giving scientists an annual record going back centuries.

Why it matters: A new epoch would represent a new reference point for how scientists understand Earth's history and trajectory — especially the impact of human-caused climate change.

  • Epochs, eras and ages frame scientists' views of Earth's evolution — the emergence of plants and the extinction of dinosaurs, the breakup of supercontinents and natural changes in global temperatures.
  • They also provide a backdrop for researchers to predict future changes.

Between the lines: "[F]or Indigenous people, and for many colonized peoples across the globe, the end of their world already occurred," says Oreskes, who is a member of the working group.

  • But it's also true "what we are facing today, in terms of the cascading and reinforcing crises of biodiversity loss, overpopulation, and climate change" is also "grave and worth addressing," she adds.

Where it stands: The new epoch isn't a done deal yet — the Anthropocene is, for now, still just a proposal.

  • Some scientists, including many who study climate change, already use the term widely. But it will be up to geologists to decide whether it is a unique epoch.

There is active debate about whether human-caused changes amount to a new epoch and, if so, when it began and how it should be defined.

  • Some anthropologists point to a time hundreds of thousands of years ago when humans first harnessed fire, or to the dawn of agriculture.
  • Others argue humans have been on Earth such a short time in geological terms, that we don't warrant our own epoch.
  • "The Anthropocene inflates our own importance by promising eternal geological life to our creations," Peter Brannen wrote in the Atlantic.
  • Some scientists have said the impact of humans should be categorized as an event, not an epoch.
Data: International Commission on Stratigraphy; Chart: Alice Feng and Tory Lysik/Axios
Data: International Commission on Stratigraphy; Chart: Alice Feng and Tory Lysik/Axios

Flashback: Other "golden spikes" punctuate the planet's history.

  • The start of the current epoch — the Holocene — roughly 11,700 years ago is defined by an ice core from Greenland.
  • The Cretaceous period, when dinosaurs still reined the land, ended 66 million years ago when a meteorite struck Earth, an event recorded in a cliff in Tunisia.
  • The Jurassic period's beginning about 200 million years ago is marked by the appearance of marine animals called ammonites in the fossil record at a site in the Australian Alps.

What's next: The International Commission on Stratigraphy (ICS) and then the International Union of Geological Sciences will vote to decide whether the Anthropocene should be designated a new epoch.

Go deeper: Listen to the Axios Today podcast, where host Niala Boodhoo and Alison Snyder share what kind of features are characterized in this new chapter in geological history.

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