The official marker for the start of a new Anthropocene epoch should be a small Canadian lake whose sediments capture chemical traces of the fallout from nuclear bombs and other forms of environmental degradation. That’s a proposal out today from researchers who have spent 14 years debating when and how humanity began altering the planet.

If the proposal is approved, a sediment core from Crawford Lake — which lies in a conservation area near Toronto — would become the ‘golden spike’ marking the beginning of the Anthropocene, the geological epoch in which humanity has profoundly affected Earth. Year after year, particles settle onto the lake and drift to its bottom, forming sediment layers that record environmental conditions much as tree rings do. Among the embedded contaminants are specks of fly ash— remnants from burning fossil fuels — and traces of radioactive plutonium from atmospheric nuclear bomb testing.