Conserving sensitive environments can yield clues about Earth’s history, says Brock prof

When Lloyd Crawford sold the lake and surrounding forest his family had enjoyed for generations to the then-Halton Region Conservation Authority, little did he realize the momentous impact the humble sale would have on Earth’s history.

Fifty-five years ago, few could have known that the small but very deep body of water contains clear, strong evidence of what Francine McCarthy and other members of the Anthropocene Working Group suggest should be a new epoch on the geologic timescale: the Anthropocene.

The Brock Professor of Earth Sciences, who has been leading research teams in the area for decades, says she is grateful for Crawford’s conservation instincts.

“In 1969, Lloyd decided that the land was too precious to sell to developers,” says McCarthy. “It’s plausible he got a lower price than a developer might have been willing to give him.”

Old documents from researchers filed in the 1970s at what is now known as Conservation Halton refer to Crawford Lake as being “a unique ecological gem” having a “delicate ecology” that must be protected “for future generations to enjoy.”

What makes the location special is that, because of its 24-metre depth and narrow circumference, the lake bottom is completely isolated from the atmosphere, enabling distinct, undisturbed layers of sediment to accumulate annually.

The sediment contains the remains of algae, zooplankton and other dead organic material. During the summer, as the water warms, dissolved calcium and carbonate ions from the surrounding rocks form small calcite crystals that sink to the lake’s bottom, creating a white layer on top of which more organic material is deposited.

“So, 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.”

McCarthy and her team can look back thousands of years through samples collected by freeze coring, which involves dropping an aluminum tube filled with dry ice and ethanol into the lakebed so that the layers stick to the tube.

Evidence of nuclear bomb testing during the Cold War is preserved in geologic records, peaking in 1963, says McCarthy. Other materials — including fertilizers, fly ash, plastics and greenhouse gases, among others — arising out of human activities are also preserved in the geologic record at various sites around the world, recording the Great Acceleration when there were few controls on emissions.

A global team of experts will decide upon the location on Earth — Crawford Lake being one of the sites under consideration — where these changes are most distinctive and propose that candidate to the International Commission on Stratigraphy as the ‘golden spike.’

The golden spike is 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.

The fact that Crawford Lake is in the running can be directly attributed to the value of conservation, says McCarthy.

“There are very few sites on the planet where the changes to Earth systems in the mid-20th century are so evident, and one of them could have been lost if Lloyd Crawford had sold his land to developers,” she says.

While the recent Anthropocene “paradigm-shifting” research is “so exciting,” the lake has yielded many other secrets throughout the decades, says Hassaan Basit, Conservation Halton President and Chief Executive Officer.

He refers to studies in the 1970s in which researchers found corn pollen in the Crawford Lake sediment layers, a sign of early cultivation. That discovery led to archaeological digs unearthing the remains of a 15th-century Indigenous village consisting of 11 longhouses and more than 10,000 artifacts. Three longhouses have been reconstructed.

“What we’ve been able to do over the years is not just preserve this site, but also to use it as a base for education,” says Basit. “Schoolchildren come all week long and get to have a really immersive experience with the site.”

Basit says the boardwalk that’s been constructed all around Crawford Lake enables visitors — the revenues from whom fully fund the area — to enjoy the surrounding forest and the lake that contains the “memory of the planet.”

“There are lots of these kinds of spaces all across Ontario that are unique either from a geological perspective or the ecology and also the human history that is captured within these areas,” says Basit.

“Preservation is critical not just to enjoy these areas today and in the future, but also for them to be able to tell those stories from our past,” he says.

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