Humans have tipped the planet into a new era and Lake Crawford, near Toronto in Canada, is proof of this. This site was chosen this Tuesday evening by The Anthropocene Working Group (AWG) as a world reference for the beginning of the Anthropocene, a name proposed in 2002 by Paul Crutzen, Nobel Prize in Chemistry. If the transition to this new geological age will be difficult to be formalized by the International Commission on Stratigraphy (ICS), one thing is certain: a rupture did occur in the last century. The Holocene conditions that allowed humanity to flourish on Earth are disappearing. Human activities – which generate microplastics, eternal chemical pollutants, invasive species, greenhouse gases, etc. – have upset the natural balance of the planet, causing profound and difficult to predict disturbances.
Christophe Bonneuil, historian, research director at the CNRS and director of the Anthropocene collection at Editions du Seuil and Catherine Jeandel, oceanographer, research director at the CNRS and member of The Anthropocene Working Group shed light on this new period in the history of the Land and the importance of Lake Crawford as a reference site.
First, what exactly is the Anthropocene?
The Anthropocene is a new period in the history of the Earth in which human activities are considered to be the cause of profound upheavals. “In the past, in high school, we learned that the history of the Earth was so long, over four billion years, that human activities, similar to a mosquito bite, could not change anything, explains Christophe Bonneuil. What mattered was the variations of key factors, the Earth’s orbit around the Sun, plate tectonics, volcanism… For the first time, we are creating a new period that considers human activities as a key factor. which is as important as other extra-human parameters such as the activities of the sun. The Anthropocene is the age of the Earth in which humans became a geological factor. »
Why Lake Crawford in Canada?
The Canadian lake was chosen as the physical embodiment of the Anthropocene by the task force, geologists who have been working since 2009 to gather evidence for the shift to a new geological epoch. Among the finalist sites were a bay in Japan, mud from a crater in China, traces in an ice core or those on coral reefs. The sediments of Lake Crawford, extraordinarily stable because the waters at depth and at the surface do not mix, “reflect the tipping point in Earth’s history when the Earth system stopped behaving as it had for 11,700 years, ”explained Francine McCarthy, a Canadian professor during an online press conference on Tuesday, relayed by AFP.
Why was it necessary to find a reference site?
“Whatever the geological age that is characterized, it is necessary to define a sedimentary series which records the variations of curves with a fairly high resolution”, defines Catherine Jeandel. There are reference series for all geological ages and a number of these ages have their reference site. “We hope to find this series in other places, she continues. There are the main tracers of the Anthropocene, in this case radioactive fallout, and the secondary tracers, things that can be found almost everywhere and which allow you to say “we are at about this level”. . »
Why is the formalization of this new geological epoch so difficult?
“It took fifty years to validate the Holocene. This period had been proposed in the 1830s by the first geologists who worked on the cycles of glaciation, notes Christophe Bonneuil. It is not surprising that geologists, who work over hundreds of millions of years, reflect before validating the Anthropocene which would only be seventy years old or two hundred years old”. Some believe that the technical criteria are not met to qualify the Anthropocene as a new “epoch”, even if they recognize a rupture.
“Part of the geological community says it’s too early, confirms Catherine Jeandel. A geological age, in general, covers the birth of a species and an extinction. To determine a geological age, you need a widely used tracer. And the most common tracer is radioactive fallout. From the time when there were nuclear air tests in the 1960s, it was distributed throughout the planet thanks to the homogenization of the atmosphere. We find them everywhere at this level. Which gives it great strength to determine an Anthropocene age,” she says.
We have the age -the 1960s-, we have a reference site -Crawford Lake-. Even if the scientific community does not immediately validate the geological time, the observation is there: “For two million years that there is the genus Homo on Earth, we have never been confronted with a planet which is changing so quickly,” concludes Christophe Bonneuil.