Why this lake in Ontario was chosen to mark a new geological era

MILTON, Ont. – Crawford Lake – deep, still and sacred to some – kept the score.

Seven centuries ago, when nearby native farmers began growing maize and squash, pollen grains from these crops fell into the lake waters and sank to the deepest reaches, a record of human presence laminated in layers of murky sediment.

When European settlers arrived 500 years later, the lake recorded evidence of their activity – clearing forests, building a sawmill to pump out shingles and planks. Sawdust and ragweed pollen, a plant that took advantage of the newly cleared land, settled in the depths of the lake. The color of that sediment changed as the settlers changed the landscape.

But it wasn’t until about 1950 that Crawford Lake began to record upheavals on a different scale – changes reflected around the world, and with greater consequences.

The term “Anthropocene” is used in different ways by different people, but it always refers to the period when the profound and harmful effects of humanity began to affect every part and process of our planet.

In recent years, scientists have debated whether to make the Anthropocene official—or to declare a new geological epoch defined by human influence. For that they need a representative place, a place in the world that shows and typifies the shift. The site would be marked with a “gold dot”, the internationally agreed starting line of the era.

On Tuesday, an international group of scientists announced that Crawford Lake is the site of the Anthropocene: Southern Ontario’s peaceful record holder is now also the world’s.

“It’s peaceful. It doesn’t look like it’s been affected,” Francine McCarthy, an earth sciences professor at Brock University, said in late June as she overlooked the lake. McCarthy led ‘Team Crawford’ and collected and published evidence needed to make the lake a candidate.

But nowhere on Earth, no matter how pristine, has been immune to these changes, she added.

“There it is, with the really clear signature of what humans have inadvertently done to the environment.”

Tuesday’s announcement doesn’t yet make the Anthropocene official, at least not by the standards of the International Commission on Stratigraphy, the scientific body charged with defining ages, epochs and other units of the geological time scale.

After more than a decade of debate and a deluge of publications, at least three more rounds of voting must take place before the Anthropocene can be officially ratified at a Congress scheduled for August 2024 – rapid progress for a field accustomed to counting time in millennia. to measure. A final thumbs up is not guaranteed.

Regardless of the outcome, choosing Crawford Lake as the global marker of the Anthropocene opens “a really valuable conversation,” says Soren Brothers, Allan and Helaine Shiff Curator of Climate Change at the Royal Ontario Museum, where one of the lake’s sediment cores has been kept frozen.

“What we’re doing is really important for the planet,” Brothers said.

“With places like Crawford Lake, you can see it on a local scale and you can see it on a global scale, all in the same timeline. It’s almost a cliché to say local is global. But it’s nice to see that that’s very is clearly recorded, with evidence.”

Crawford Lake has some unusual features that make it vividly capture the passage of time. It is very small and very deep, with a depth of almost 24 meters at its deepest point. It is also what is known as a “meromictic” lake.

In typical lakes, the upper water layers mix with the deepest layers. But in Meromictic lakes the deepest waters do not mix; the bottom layer is almost like an isolated body of water. Because the deep waters are protected from disturbances above, whatever falls into the lake settles in the sediment at the bottom in a slow, gentle drift.

Crawford Lake is also set in limestone rock in the Niagara Escarpment. When the weather gets warm, small crystals flake off these rocks and rain down to the bottom of the lake, forming a distinct white coating.

For scientists, all of this is incredibly helpful. Sediment cores recovered from the lake bed depict individual years as tree rings, with white bands of crystal deposits marking each summer. The thickest layer in the 20th century was deposited in 1935 during the Dust Bowl, and researchers can count the layers above it year after year.

If you go up about 15 layers from that thicker line, you end up in the early 1950s — the period, according to the scientists who had to decide whether to bring forward the Anthropocene as a new epoch, when human influences on the planet started to become recognizable all over the world. globe, all at once.

At Crawford Lake and the other locations considered gold spike candidates, the clearest signal picked up in the early 1950s is a large spike in plutonium isotopes — fallout from the testing and detonation of atomic bombs, some halfway across the planet.

“But the important thing here is you have all these other markers that reflect the big changes on the planet,” said Colin Waters, the chair of the Anthropocene Working Group, a body that’s part of the International Commission on Stratigraphy and was founded in 2009 to consider this new era. “So the increasing consumption of fossil fuels, the greater use of nitrogen fertilizers and the increased global trade that spreads species across the planet … All of these things are changing very quickly.”

The sediment layers of Crawford Lake from the early 1950s capture a rapid increase in fly ash, byproducts of burning coal and other fossil fuels at very high temperatures. These particles are likely blown out of Hamilton, with its steel mills and other heavy industry, McCarthy says.

The lake has cushioned adverse environmental impacts, but it also records positive changes. By the 1970s, the concentrations of both plutonium isotopes and fly ash particles are declining, evidence of the success of both global and local policies. The Non-Proliferation Treaty began reducing the number of nuclear weapons worldwide in this decade, and stricter environmental regulations limited emissions at Hamilton steel mills and beyond.

Humans are intimately connected to their environment, but the relationship doesn’t have to be a negative one, Brothers said, pointing to the corn pollen left behind by native growers.

“Then do we want to start this conversation by saying that people are always in a negative balance with the environment, or do we want to take that to another place?”

Halton Region Conservation Authority acquired Crawford Lake in 1969 and has managed the site ever since. The area already receives about 100,000 visitors and about 30,000 students a year, said Hassaan Basit, CEO of Conservation Halton; preparations are being made to manage the increased traffic while protecting the lake.

“It’s a magical place,” Basit said.

“That’s kind of the real reason why conservation authorities like mine play such a vital role in preserving these landscapes, because of what they can teach us.”

McCarthy also clarified that the actual gold spike would not be installed at the bottom of the lake or anywhere on site. Gold spikes – which are actually made of brass – often get lost in publicly accessible places. The spike, if and when designated, would go to the Canadian Museum of Nature in Ottawa, where the lake’s official core is stored in a highly protected cryogenic facility.

Everyone associated with Lake Crawford calls it a special place. For Catherine Tàmmaro, a multidisciplinary artist and member of the Wyandot of Anderdon Nation and Little (Spotted) Turtle Clan FaithKeeper, the connection to the lake is “deep” – ancestral, spiritual and scientific.

The area is important because the ancestors of her people lived there, Tàmmaro said, but also because it is a place that predates contact with Europeans and there is no clear evidence of conflict or warfare.

“So it is a place where people lived under the peace for contact. And for that reason, I think it has a lot of spiritual resonance.”

The last time scientists retrieved a sediment core from the lake, Tàmmaro invited the researchers to participate in a ceremony with her and other indigenous people present. It was a difficult moment, one she considered surgery—painful, but ultimately revealing and helpful.

The story is “buried, like so many stories about the history of this place, of Ontario,” Tàmmaro said. “That story needs to be told. The understory must be understood. The real story needs to be understood by everyone who lives here.

“Those layers — it’s tragically eloquent to ask Earth to reveal to us the damage that’s been done.”

Kate Allen is a Toronto-based reporter covering climate change for the Star. Follow her on Twitter: @catecallen

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