An Epoch Proposal

Mud cores from a lake in Canada hold the geochemical markers proving a distinct geological epoch began in 1950, according to a group of scientists yesterday. The announcement is the latest step in a decadelong process seeking to delineate humanity's impact on Earth, an era dubbed the Anthropocene, or human age.

Geologists designate eras in our planet based on demonstrable shifts over time in the makeup of rocks, ice, and sediments (see interactive timeline). A special working group of geologists proposed Crawford Lake outside Toronto as the site with the clearest material signature of the shift from the Holocene epoch (which started about 11,000 years ago) to the Anthropocene in the mid-20th century.

The small, 78-feet deep meromictic lake—where upper water layers don't mix with the lower—has preserved a millennium of particulate in its sediment, including markers of nuclear tests, fossil fuels, and more. Final approval of the designation requires several more levels of votes over the next year.

Learn more about the scientific debate over the designation here.