Seemingly tiny Crawford Lake, just outside of Toronto, Canada, is unusual. Locals usually walk the dog and eat their famous maple syrup pancakes, but it’s not a special place for that. The lake appears small, barely 250 meters from end to end, but it hides an extraordinary depth of 24 meters. It is what is technically called a meromictic lake: its surface water does not mix with that of its bottom, which has remained undisturbed for centuries. Sediment from the atmosphere accumulates like layers of lasagne on the ground every year. An international team of scientists announced Tuesday that Crawford Lake is the place on earth where the beginning of a potential new geological epoch around 1950 is best estimated: the Anthropocene.
Geologist Francine McCarthy shares a photo of a sediment sample from the depths of the lake. It’s a vertical specimen of just under 90 centimeters, but it tells the story of Crawford year after year since the 13th century. It is very easy to see the passage of time. In winter the lake freezes and dark organic matter settles on the bottom. In summer, the calcium and carbonates dissolved in the water crystallize from the surrounding limestone rocks due to the heat and form a white layer of calcite on the bottom. This succession of light and dark lines is a perfect calendar, an underwater history book showing that in 1950 human influence began to change everything. It is the so-called Great Acceleration, the moment when nuclear bomb testing, massive burning of coal and oil, and disappearance of species began to leave clear marks on the planet’s skin.
Humanity officially lives in the Holocene, a geological epoch that began more than 10,000 years ago, after the last Ice Age. In 2000, the Dutch chemist Paul Crutzen, winner of the Nobel Prize in Chemistry for the elucidation of the destruction of atmospheric ozone, and the American biologist Eugene Stoermer suspected that human influence on the planet had triggered a new epoch: the Anthropocene. The idea has since caught on, but the certifying body, the International Union of Geological Sciences, has yet to make a decision. A team of experts, the Anthropocene Working Group, has been investigating since 2009 whether humanity has actually changed its age. In 2016, these researchers proclaimed that the Anthropocene was a geological reality. This Tuesday, at a conference in Lille, France, the group’s leader, British geologist Colin Waters, announced that Lake Crawford was the best model to observe the beginning of this worrying era marked by human contamination.
The scientific community, through the International Commission on Stratigraphy, selects reference points that mark the beginning of new geological stages. The beginning of the Holocene is officially symbolized by an ice core recovered in Greenland in 2003 at a depth of almost 1,500 meters. This frozen sample, kept at the University of Copenhagen (Denmark), shows rapid warming of the climate associated with a change in certain chemical elements. The reference points of seven geological stages are in Spain. In the city of Fuentelsaz (Guadalajara), for example, the beginning of the Middle Jurassic around 175 million years ago can be proven better than anywhere else. On the coast of Zumaia (Guipúzcoa) there are two official boundaries between the stages of the Paleocene. All of these points are marked by golden nails placed in solemn ceremonies.
Obtaining a sediment core from the bottom of Crawford Lake. TIM PATTERSON / CARLETON UNIVERSITY
A dozen locations vied for the Anthropocene’s golden nail, including remote Lake Sihailongwan, nestled in the crater of a Chinese volcano, and the sea mud of Japan’s Beppu Bay, both of which made the final vote. “Lake Crawford is where the beginning of the Anthropocene is best documented today,” says geologist Alejandro Cearreta, the only Spanish member of the international working group. “The best indicator is plutonium-239. “All sediments after 1950 contain plutonium, either in the park next to your house or in Crawford Lake,” explains Cearreta, professor of paleontology at the University of the Basque Country.
The geological authorities are in no hurry to announce the official beginning of a new epoch. Cearreta explains the complex protocol, which can stretch for years. The Anthropocene Working Group will submit its final proposal, including Crawford Lake, in the coming weeks. The Subcommittee on Quaternary Stratigraphy will examine the conclusions and, if they share them, forward them to the higher level: the International Stratigraphic Commission. If at least 60% of its members vote to declare the beginning of the Anthropocene, the decision has yet to be ratified by the International Union of Geological Sciences. “The process can be stopped at any time,” warns Cearreta.
The Royal Spanish Academy, anticipating the discussion among professionals, already takes into account the end of the Holocene and the beginning of the Anthropocene in the dictionary of the language. The College of Geologists has harshly denied this. “The Royal Spanish Academy has traditionally been a reputable institution that worked with scientific methods. This encroachment on geology, no doubt guided by ideological interests, is frankly disheartening. declared on May 30th the college chaired by geologist Manuel Regueiro. Some experts, such as Americans Lucy Edwards and Stanley Finney, argue that it is still early to see human impact on geological strata and believe there is political pressure to explain the beginning of the Anthropocene.
Canadian geologist Francine McCarthy believes Crawford Lake will help convince skeptics. His team inserts an “ice finger” into the ground, a frozen artifact inside which is liquid nitrogen at nearly 200 degrees below zero, to which the sediments adhere. Man’s influence can be clearly seen in these leaves. Layers from the late 13th century already contain maize pollen, confirming the presence of indigenous tribes in the area. The thickest white line corresponds to 1935, the hottest summer of the so-called Dust Bowl [cuenco de polvo, en inglés], a period characterized by drought and sandstorms due to deforestation. And from 1950 the radioactivity of the atomic bombs and the pollutants from the burning of coal and oil are confirmed. These are irreversible changes that can be seen everywhere, as the Anthropocene Working Group argues. “Each time we extract an icy core from the bottom of this unique lake, it is like witnessing a birth: they are all beautiful when they first emerge. Knowing that they can share so much relevant information with us is mind-blowing,” says McCarthy.
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