Locals used to say that Crawford Lake was bottomless. Its waters ran deeper than people could reach.
These spikes are like exclamation points in the story of the planet, punctuating a tale of shifting continents, evolving species and temperatures that rose and fell as carbon levels fluctuated in the atmosphere. They mark the starts of epochs — small segments of geologic time. And they have helped scientists interpret the forces that shaped Earth’s past climates, which in turn allows them to forecast the effects of modern warming.
Crawford Lake was similarly modest — just a pretty little pool at a park in the Toronto suburbs. Schoolchildren liked to visit its reconstructed Indigenous longhouses. Locals treasured it as a quaint spot to have a picnic and watch for birds. All year long, a constant stream of dead microbes, animal droppings and other organic debris drifts through Crawford’s waters to settle on the lake bed. But during summer, when the temperature and acidity levels are just right, the water also produces crystals of a white mineral called calcite that fall to the lake bed, forming a thin white cap.Article content
First, researchers had to tether a wooden raft in the deepest part of the lake, right over the spot they wanted to sample. Finally, it was time to pull the corer back up. Clinging to its face was a five-foot slice of mud, cut from the lake bottom like a piece from the centre of a cake. By counting down from the top of the core, and analyzing the environmental markers within each layer, scientists can travel through time — revealing how Crawford Lake and the world have changed since long before written records began.
Sediments from subsequent eras showed Europeans’ growing influence on the landscape. White pine pollen counts dwindled as people cut down trees. Traces of ragweed marked how different species flourished in the cleared land.Article content Still more sediments recorded irreversible losses. Certain microbe species were eliminated locally. The amount of elm pollen plummeted — a consequence of the invasive fungus that was decimating North America’s tree populations at the time.
The same evidence appears all over the planet, in every potential golden spike site the Anthropocene Working Group has examined. Peat bogs, ocean basins, the skeletons of coral reefs — even the ice of Antarctica has been permanently tainted by human pollution. And Crawford Lake had already endured so much painful history. Dredging up its sediments — even for science — felt like another invasion.
Before the Anthropocene — and the lake — can claim a place in geologic history, the proposal must undergo several more rounds of voting. And not all geologists are convinced the Anthropocene belongs on Earth’s 4.6-billion-year timeline. Some say this period of overwhelming human influence has been too brief to know whether it is truly an epoch, a span that typically lasts millions of years.
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