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Crawford Lake is so small it takes just 10 minutes to stroll all the way around its shore. But beneath its surface, this pond in southern Ontario in Canada hides something special that is attracting attention from scientists around the globe. They are in search of a distinctive marker buried deep in the mud — a signal designating the moment when humans achieved such power that they started irreversibly transforming the planet. The mud layers in this lake could be ground zero for the Anthropocene — a potential new epoch of geological time.