From climate change to species loss and pollution, humans have etched their impact on the Earth with such strength and permanence since the middle of the 20th century that a special team of scientists says a new geologic epoch began then.

Called the Anthropocene — and derived from the Greek terms for “human” and “new” — this epoch started sometime between 1950 and 1954, according to the scientists. While there is evidence worldwide that captures the impact of burning fossil fuels, detonating nuclear weapons and dumping fertilizers and plastics on land and in waterways, the scientists are proposing a small but deep lake outside of Toronto, Canada — Crawford Lake — to place a historic marker.