Science & Tech
Hidden beneath the surface of this Ontario lake is an archive of the earth’s history sealed in mud
Update: Since this story’s publication, the governing body for geologists has agreed that the Anthropocene epoch will not be added to the timeline of Earth’s history. On March 20, 2023, the International Union of Geological Sciences announced that it is upholding a decision made earlier this month by a group of geoscientists. In early March, the Subcommission on Quaternary Stratigraphy, voted 12 against, four in favour and two abstention to reject a proposal that would have established the current era, in which humans are altering the planet, as a formal epoch in Earth’s geological timetable.
The planet’s crust is an archive of time and catastrophe. Its layers carry evidence of asteroid hits, mass extinctions, toxic changes to the atmosphere and continental ruptures.
Now, an international team of the scientists who painstakingly catalogue those layers has declared that Earth moved into a new phase of its history about 73 years ago and that the best piece of crust in the world to represent it is a tiny lake in southern Ontario. They have nominated Crawford Lake, barely an hour’s drive west of Toronto, as the global example of the beginning of the Anthropocene, the epoch when humans began irrevocably shaping the planet’s fate.
Its nomination still needs to be voted on by three higher bodies of geologists over the coming year, but if they, too, approve the candidacy, Crawford Lake will be endowed with the “golden spike,” a literal brass marker that signifies that the planet shifted, in about 1950, from one unit of geological time to the next.
“If people see that stratigraphers, a conservative bunch of geologists, are willing to put a line on the timescale and call it by the name that recognizes — that admits — the role of humans as a causal agency, then that’s mammoth,” Francine McCarthy, a geologist at Brock University, said recently, sitting on a bench beside Crawford Lake. She led the team of about 75 scientists who made the case for the site to win the candidacy.
Crawford Lake was up against 11 others. They spanned five continents and included Antarctic ice, tropical corals and mountain peat bogs.
Scientists were surprised by how consistently each of the 12 sites showed the global marks of human activity, explained Colin Waters, chair of the Anthropocene Working Group, the body of stratigraphers established in 2009 and charged with choosing the best site. He made the pronouncement during a press conference last week.
“When you combine them and read the stories that they tell you, it shows you that there is this very significant and very rapid change to the environment in a very short period of time,” said Waters, a geologist at the University of Leicester in the United Kingdom.
If the Anthropocene Working Group has its way, stratigraphers will eventually proclaim that the planet has entered the Crawfordian age (by protocol, named after the site of the golden spike) of the Anthropocene epoch. It will be only the 39th new epoch ever proclaimed in the planet’s 4.6-billion-year life.
It represents a point of no return, geologically speaking. Earth will have broken in fundamental ways from the Holocene epoch that began during the Stone Age about 11,700 years ago, a long period of climate stability that supported the growth of human civilization.
Unlike other transitions in the geological time scale, some of which affected the planet’s ability to support life, this one does not involve contortions of the crust, explained Simon Turner, secretary of the Anthropocene Working Group and a senior research fellow at University College London.
“The effects are very much atmospheric, soil. Essentially, the living parts of the planet are what have been so massively affected by the Anthropocene. And in that sense, it is on a par with some of these major planetary events that have occurred in the past.”
That means the problem is not merely local, but global, Jürgen Renn, director of the Max Planck Institute of Geoanthropology in Jena, Germany, explained at the press conference.
“And so I think we have to take it as a challenge for human creativity and ingenuity,” he said.
Markers of the new epoch are linked to what’s known as the Great Acceleration. That’s the period after the Second World War when human activity began to overwhelm Earth’s operating systems. Population surged. So did industry, driven by burning fossil fuels, which loaded the atmosphere with carbon dioxide. Add to that plastics, nuclear tests, nitrogen-based fertilizers and species depletions.
All of it showed up in Crawford Lake, in a precise, year-by-year record, explained McCarthy, who is also a voting member of the Anthropocene Working Group. That’s because this humble little lake’s chemistry is among the rarest in the world. For one thing, the lake is meromictic, meaning its top and bottom layers never mix. The ratio of its depth of 24 metres and its surface area of 2.4 hectares prevents mixing.
But in addition, the bottom layer contains oxygen. Geologists know of no other lake in North America with that combination and few others in the world.
The result is that material falls to the bottom of the lake and is sealed by deposits of calcite in distinct couplets of layers, called varves, separated into summer and winter seasons. Each layer can be dated to the exact year, critical to the nomination for golden spike.
“This lake is kind of like looking into the secrets of the planet,” said Hassaan Basit, president and chief executive of Conservation Halton, the private organization that owns the 222-hectare conservation site containing the lake. It forms part of the Niagara Escarpment UNESCO Biosphere Reserve.
Crawford Lake was already special long before the planet’s stratigraphers got involved. Shortly after the conservation organization bought the lake in 1969, studies revealed its unusual chemistry. That led to the first sampling of its sediments, which, in turn, led to the finding in the 1970s of corn pollen in layers dating to the Middle Ages, centuries before colonization.
That triggered archaeological work to check for the presence of Indigenous settlement near the lake from that era. The result was the discovery of intricately crafted longhouses dating from the 15th century. Three replicas now stand on the site a short walk from the lake, along with interpretive displays.
“The lake was there and it was being studied and it was slowly unveiling these secrets,” Basit said.
McCarthy became involved in 2011 when her graduate student studied a new core sample for a master’s project. On the student’s graduate committee sat Martin Head, a biostratigrapher at Brock who has a long-term involvement with the International Commission on Stratigraphy, the body responsible for setting the geological timescale.
He also sits on the Anthropocene Working Group that, in 2019, launched a global quest to find the golden spike candidate. Head remembered the varves at Crawford Lake and asked McCarthy if she would be willing to take on the work to prepare a submission on the site.
“And I said, ‘sure,’ and the rest is history,” she explained.
Her first call was to Tim Patterson, professor of earth sciences at Carleton University in Ottawa and a specialist in taking freeze cores from lakes, a process critical to getting perfect, precise layers from Crawford Lake. The sediments are fragile and filled with gas. If brought up without freezing, they explode. So he fills a corer with dry ice, which freezes its metal face. Sediments dating back 1,000 years freeze to the face and can then be brought up to the surface and analyzed.
His student, Krysten Lafond, developed a technique to make very high-resolution images of the layers, stitch them together and enlarge the composite to the size of a house. That allowed extremely precise identification of each year of calcified sediment.
Analysis of the cores showed that the Indigenous settlement in the 15th century somehow changed the lake enough to create the calcite layers between each year of sediments, Patterson said. Once they abandoned the site, the lake’s chemistry shifted again, only to resume yearly calcite deposits in 1874 when European settlers arrived.
By 1950 or so, a rapid, dramatic increase of carbon-based particles shows up from industrial processes, including coal-fired steel-making in a nearby Hamilton foundry, as well as a rapid rise in plutonium from nuclear testing, a change in nitrogen isotopes from fertilizer use, and the chemical fallout from acid rain.
How Earth will function during this new phase of its life is difficult to predict with certainty. Such abrupt and deep planetary change gives species little time to adapt, including humans. Heat waves, sea level rise, ocean change, shifts in arable land and in precipitation are already evident, just seven decades into the presumed new epoch.
“We really are pushing the boundaries here,” said Head. “And the planet is moving into uncharted territories. There’s no question.”
He said Earth’s systems have broken not just with the Holocene epoch, but also with some of the norms of the longer, 2.58-million-year Quaternary period the Holocene is part of, such as the carbon load in the atmosphere.
Some of the handfuls of stratigraphers who will vote at the three remaining levels vociferously disagree with his assessment, he said.
“They are stratigraphers who primarily work with deep time, so they don’t really see these things, even when they’re close up to them,” he said. “So it’s very unfortunate and I don’t think they fully appreciate the responsibility we have to make the right decision about the Anthropocene.”
One option is that they will reject the entire proposal. Or they could reject just the Anthropocene and proclaim the Crawfordian era as part of the Holocene. Head and his colleagues on the working group are pressing for a third option, which is to enshrine the Anthropocene, the new age of humans, as the youngest geological age, with all its unknowns.
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