When scientists read human history in the mud of Lake Crawford

It is clearly a small lake like there are thousands in Canada. But what lies beneath the surface makes it extraordinary: the exceptional preservation of its geological strata makes it the new global reference for the Anthropocene.

For years, geologists have sought to establish a place in the world (dubbed the “golden nail”) that constitutes the best benchmark for this proposed new geological epoch, synonymous with the dramatic impact of human activity on the planet.

That’s why this place is a small lake in Ontario, on the outskirts of Toronto, announced on Tuesday the Working Group on the Anthropocene, set up by the International Commission on Stratigraphy (ICS).

Local legend claims that this lake has no bottom. Yet its depth is beset by an unparalleled richness: sediments show, more than anywhere else on Earth, that man has transformed the planet on all levels. This included at the geological level, in the physical makeup of the Earth.

“The lake is very deep, but not very large. This means that the water does not mix with the bottom, so the sediment that accumulates is not affected,” explains Francine McCarthy of Brock University, whom AFP met in April when the last samples were taken. Samples for choosing a golden nail.

Coal and oil

For centuries, Lake Crawford has quietly absorbed signs of change from the outside world. Whatever floats to the surface ends up in the depths of the lake.

The first men to make their mark on the lake were the Iroquois villagers who built homes on the shores in the 15th^H a century. Then, the sediments show the increasing influence of Europeans on the landscape (logging, new species, etc.).

Then in XX^H Century, it is the turn of the black ash—from the combustion of coal and oil—to accumulate in the lake, in this region as cities develop and industrialize. Heavy metals such as copper and lead also gradually appear in the mud.

“We can observe local disturbances, regional events, such as pollution,” confirms Paul Hamilton, a researcher at the Canadian Museum of Natural History. The sediments also “document changes on a global scale, in other words the fallout from chemicals in the atmosphere.”

“Each year has its own personality, just like the people,” exclaims Francine McCarthy, outlining the annual contours of the geological “core” excavated from the lake.

These samples act as markers, and extracting them requires ingenuity, precision, and speed.

Tim Patterson is a researcher at Carleton University in Ottawa and his team are specialists in this field. To recover without damaging the layers of sediment from the depths of the lake, they get busy filling large metal tubes with dry ice and alcohol.

Sur ces longs batons glacés de pres de deux mètres et 15 cm de large, qui sont immergés au fond du lac pendant une demi-heure, les sediments vaennent se coller pour former une succession de lignes bien distinctes pour chaque année, as his cernes d ‘tree.

Great acceleration

During the April samples, it was the traces of plutonium that particularly interested Tim Patterson.

The beginning of the Anthropocene has already been proposed in 1950 to “shine light on something completely unique in world history: nuclear testing,” he explains.

“Humans have never done this before. And it leaves a mark, not only regionally, but globally, ”adds the researcher.

and mid XX^H The century will also witness this pivotal moment when everything was swept away, when humanity entered a phase of great acceleration (consumption, production, pollution, etc.).

“Things went the same way for 12,000 years. Then suddenly, all of a sudden, everything changed. Today, the Earth has been modified enough by human activities that it behaves differently,” notes Francine McCarthy, who has worked at the site since 1984.

The official endorsement by global geological authorities that Earth emerged from the Holocene, the period beginning about 12,000 years ago at the end of the last ice age, in the Anthropocene, the “age of man,” remains uncertain.

But this enthusiast remains optimistic: “If the geologists, who discovered plutonium and oil in rocks, accept that there is fundamental change due to man, then perhaps action will be taken.”

Let’s see in the video