Two Brock University professors are among a body of international experts that has selected a location on Earth that will allow the Anthropocene to be defined as a new epoch in geologic time.

Brock Professors of Earth Sciences Francine McCarthy and Martin Head, and Carleton University Professor of Earth Sciences Tim Patterson, head up a team that has been studying the geology of Crawford Lake in Milton, Ont., for many years.

On July 11, the Anthropocene Working Group (AWG) — of which McCarthy and Head are voting members — announced its choice of Crawford Lake over 11 other possible sites as the location that best shows the boundary of the proposed Anthropocene, brought about by major changes to Earth through human activity.

“My main reaction to the news is relief,” says McCarthy. “I’m happy not just for me, for my colleagues and their students from a number of institutions who have been working really hard, but frankly, I’m happy for the planet.”

During their long-running research, the multi-institutional team gathered sediment from Crawford Lake through a process called ‘freeze coring’ in which organic material freezes to the outside of a hollow tube, filled with dry ice and ethanol, that is dropped into the lake’s muddy floor.

From the cores, researchers can see annual layers of sediment called varves that resemble tree rings. Varves from the mid-20th century onward contain deposits of human-made byproducts such as plutonium-239, microplastics, fertilizers and fly ash.

Crawford Lake is classified as a meromictic lake, meaning its layers of water don’t intermix. McCarthy says this characteristic, and the deepness of the lake, have enabled scientists to get an accurate record of the area’s human and natural history.

“Crawford Lake’s unique varving patterns lead to the exceptional, wonderful preservation of all of the things in it without being disturbed,” says McCarthy. “So, we can sample every year and tell you what was going on in the water, the atmosphere, the watershed.”

Head hails the choice of Crawford Lake as being “a very important step forward in the defining of the Anthropocene as a new geological time and the culmination of a huge amount of work.”

He says rapid changes in population growth, industrialization and globalization following the Second World War and the use of the atomic bomb have significantly altered the Earth.

“It’s really important that we acknowledge a momentous planetary shift in the mid-20th century as a geological term,” Head says. “Otherwise, people will think that this is really just business as usual, that the Holocene Epoch has not ended, and the changes that have occurred in recent memory are simply incremental, which we know is actually not the case.”

The July 11 announcement is the first of many steps that need to occur before a new epoch can be officially declared, a process will take “many months,” says Head.

The AWG will forward its Crawford Lake recommendation to the International Subcommission on Quaternary Stratigraphy, of which Head is vice-chair.

The Subcommission could either accept or reject Crawford Lake as hosting the ‘golden spike,’ an internationally agreed upon reference point in rock or sediment layers that defines the lower boundary of a new stage in the geologic time scale.

If they do accept Crawford Lake, the Subcommission could either choose to recommend that the golden spike only define the beginning of the ‘Crawfordian Age’, where it would be part of the current Holocene Epoch, or define a new Anthropocene Epoch as well.

“We’re hoping the Subcommission agrees to at least a golden spike for the Crawfordian Age; I’m hoping for the Anthropocene,” says McCarthy.

Once the Subcommission makes its choice, it goes to the International Commission on Stratigraphy for a full vote. That decision is then forwarded to the International Union for Geological Sciences, which has the final say.

McCarthy says she is “happy that we have a good proposal.”

“We’re doing our level best to get the public to understand we’re at a critical juncture right now where there is probably still time to turn the ship around before it hits the iceberg, so to speak, but we need to get that message out in a way that is convincing and understandable for people who vote and those who make decisions,” she says.

A small lake in a conservation area in Halton Region is yielding big clues to a shift in Earth’s geologic history.

At the bottom of deep, serene Crawford Lake are layers of sediment showing how human activity has changed the Earth to such an extent that the planet entered a prospective new epoch in geologic time: the Anthropocene.

Brock University Professor of Earth Sciences Francine McCarthy leads a research team that has, over the years, collected core samples of Crawford Lake’s sediments to study these changes.

This is part of a global effort led by an international group to identify evidence that a major change in Earth’s history occurred in the mid-20^th century.

The Anthropocene Working Group examined numerous locations on Earth, including Crawford Lake, that show the clearest boundary between the Holocene and the proposed Anthropocene.

These and many other materials are evidence of ‘the Great Acceleration,’ a marked upturn in indicators of population growth, industrialization and globalization, following the Second World War.

“The Anthropocene Working Group has decided to use plutonium fallout from the Cold War and nuclear proliferation in order to define the Anthropocene,” says McCarthy. “Our plutonium record is very nice; it’s textbook.”

The research team’s leadership consists of McCarthy, Brock University Professor of Earth Sciences Martin Head, and Carleton University Professor of Earth Sciences Professor Tim Patterson.

Patterson and his students have expertise in collecting freeze cores and conducting core analysis, “which complements the work of Dr. McCarthy, who focuses on understanding the limnology of the lake and the depositional processes that have taken place there to form the varve layers that we see in the sedimentary record,” he says.

Included on the multi-institutional team of experts is Brock Professor of Geography and Tourism Studies Professor Michael Pisaric.

In addition to plutonium-239, other human byproducts in the lake sediments include microplastics, fertilizers and fly ash.

Sediment, which includes the remains of algae, zooplankton and other organic material, freezes onto the tube along with small calcite crystals that sank to the lake’s bottom. These crystals create a white layer each summer on top of which more organic material is deposited the rest of the year.

Freeze-coring allows the annually deposited sediment layers, called varves, to freeze onto a hollow metal tube filled with dry ice and ethanol that is allowed to sit in the lakebed for up to 40 minutes. The varves are individually sampled for analysis.

“You can count like tree rings and find 1952 or any other year that you’re interested in finding,” says McCarthy. “Because those layers are undisturbed, everything is exquisitely preserved.”

Once a site is proposed by the Anthropocene Working Group, the International Commission on Stratigraphy (ICS) can decide whether to officially define the new Anthropocene geologic epoch.

“Defining the Anthropocene as a term is crucial,” says Head who, along with McCarthy, is a member of the Anthropocene Working Group, the international body of experts voting on the location of the site. Head is also vice-chair of the International Subcommission on Quaternary Stratigraphy, which will vote on the Anthropocene Working Group’s proposal.

“I was talking to a director at the United Nations recently who explained that they use the Anthropocene as a framing concept for policymaking, but the term is not properly defined, and they need clarity,” says Head. “An official scientific definition will help the United Nations, the World Bank, the International Monetary Fund and other global bodies create policies and programs addressing climate change.”

McCarthy says that recognizing the transition from the Holocene to the Anthropocene epoch has huge implications for the Earth and future generations.

“It’s important for everyone to know that the Earth is a different place than it was before 1950,” she says. “We actually reached a tipping point, so that the way that the atmosphere, the oceans and all the systems of the Earth interact is different than it used to be.

“If we don’t recognize that those relationships and the way they interact are different, we’re not making decisions based on accurate information,” McCarthy says. “We need to act now to decide what we want to leave for future generations.”

Watch: Brock-led Crawford Lake research explores human impacts on the Earth.

Gallery: Brock-led research team collects sediment samples at Crawford Lake Conservation Area on April 13, 2023.

Read more about the Anthropocene and Brock’s research at Crawford Lake

In the media

Story by Cathy Majtenyi, photography by Stephen Leithwood, videography by Mitch Morrone, website design by Natalie Greene, content and creative direction by Maryanne St. Denis and Sébastien Marchal.