The Canadian Lake That Holds the Secrets of the Anthropocene Era

Earth's history is divided into different periods of time, based on the major events and changes that shaped the planet and its life forms.

These periods are called geologic epochs, and they are marked by physical or chemical signatures in rocks, ice, or sediments that can be dated and correlated across the world.

We currently live in the Holocene Epoch, which began about 11,700 years ago, after the end of the last ice age.

But when did the Anthropocene start, and how can we recognize it?

To answer these questions, researchers have been searching for a location that best records the human changes to Earth, and they have found it in a small lake in Canada.

What is the Anthropocene?

(Photo : FABRICE COFFRINI/AFP via Getty Images)

The Anthropocene is a term that was coined in the early 2000s by atmospheric chemist Paul Crutzen and biologist Eugene Stoermer, to describe the current geological time period in which humans have become a dominant force of global change, as per the BBC.

Humans have altered the Earth's climate, land, water, biosphere, and geosphere in ways that are unprecedented in natural history. Some of the indicators of these changes include:

• The increase of greenhouse gases, such as carbon dioxide and methane, in the atmosphere, due to fossil fuel combustion, deforestation, agriculture, and other activities. These gases trap heat and cause global warming, which affects weather patterns, sea level, ice sheets, and ecosystems.
• The spread of radioactive elements, such as plutonium and cesium, in the environment, due to nuclear weapons testing, accidents, and waste disposal. These elements have long half-lives and pose health risks to humans and wildlife.
• The proliferation of synthetic materials, such as plastics, metals, concrete, and chemicals, in the biosphere. These materials are durable and ubiquitous, but they also create pollution, waste, and toxicity problems. They can also be ingested or entangled by animals or accumulate in food webs.
• The loss of biodiversity and ecosystem services, due to habitat destruction, overexploitation, invasive species, and pollution. Humans have caused the extinction or endangerment of many species and reduced the genetic diversity and resilience of natural populations.
• The modification of land use and cover, due to urbanization, agriculture, mining, and infrastructure development. Humans have transformed more than three-quarters of the Earth's ice-free land surface for their own purposes, affecting soil quality, water availability, carbon storage, and nutrient cycles.

The Anthropocene is not yet an official geologic epoch recognized by the International Commission on Stratigraphy (ICS), the scientific body that defines the geologic time scale.

To become official, the Anthropocene needs to meet certain criteria, such as having a clear and global boundary that can be dated and correlated across different locations.

This boundary is called a Global Boundary Stratotype Section and Point (GSSP), or more informally a "golden spike".

It is usually represented by a physical marker in a rock or sediment layer that shows a significant change in its properties.

Also Read: Anthropocene No Longer Surprising with Uptick in GHG, Microplastics, PFAS -Expert Says

Why is Crawford Lake the golden spike for the Anthropocene?

Crawford Lake is a small body of water in Ontario, Canada. It is about 22 meters deep and 500 meters wide, as per The Globe and Mail.

It is also a meromictic lake, meaning that its water layers do not mix due to differences in density and salinity.

This creates anoxic conditions at the bottom of the lake, which prevent bioturbation (the disturbance of sediments by organisms) and preserve the sediments in fine layers called varves.

Crawford Lake's varves provide an extremely precise record of human influence on Earth since the 15th century. By analyzing the chemical composition and radiocarbon dating of each varve, researchers can detect various signals of human activity over time. Some of these signals include:

• The arrival of European settlers in North America around 1500 CE. This is marked by a decrease in carbon-13 isotopes in the organic matter layer, indicating a shift from C3 plants (such as trees) to C4 plants (such as corn) due to deforestation and agriculture.
• The onset of industrialization around 1800 CE. This is marked by an increase in sulfur isotopes in the calcite layer, indicating an increase in coal burning and acid rain.
• The peak of nuclear weapons testing around 1963 CE. This is marked by a spike in plutonium isotopes in the calcite layer, indicating the global dispersion of radioactive fallout from atmospheric explosions.
• The rise of plastic pollution around 1980 CE. This is marked by the presence of microplastic particles in the organic matter layer, indicating the accumulation of synthetic debris in aquatic ecosystems.

Crawford Lake's sediments also show changes in the geochemistry, ecology, and paleoclimate of the lake and its surroundings, reflecting the broader impacts of human activities on the Earth system.

Crawford Lake has been selected as the GSSP for the Anthropocene by an international committee of experts, who have been working for more than a decade to define and characterize the proposed epoch.

The committee has evaluated 12 candidate sites around the world, each with its own strengths and weaknesses, but Crawford Lake stood out for its exceptional resolution, continuity, and global relevance.

They have also proposed that the Anthropocene should start in the mid-20th century, around 1950 CE, when the human impact on Earth reached a global scale and accelerated rapidly.

This period is known as the "Great Acceleration," and it coincides with many of the signals recorded in Crawford Lake's varves.

However, the final decision on whether to officially recognize the Anthropocene as a new geologic epoch is not yet made.

The proposal still needs to be approved by several more committees within the ICS and the International Union of Geological Sciences (IUGS), which may take several years.

It also needs to be accepted by the wider scientific community and the public, which may involve debates and controversies over the scientific, ethical, and political implications of declaring a new age of humans.

Related article: Humans Have Been Living in New Epoch for Last 50 Years