Millions of years from now, will the geological record of Earth's history display evidence of a "human" epoch? Colin Waters and colleagues have accumulated a massive body of data that suggests the Anthropocene epoch is a geological phenomenon that can be identified in the stratigraphic record. Until now, the Anthropocene as a period distinct from the previous Holocene epoch has been more of an idea used to demonstrate the massive impact that humans have had on the planet's atmosphere and species. But Waters and colleagues now say in this Review that human activity has left a pervasive and persistent signature on Earth that warrants recognition as a new geological time unit. The long-lasting and widespread geological record of the Anthropocene will include stratigraphic layers full of uniquely human products such as concrete, elemental aluminum, and plastics, for instance. Carbon particulates from atmospheric pollution, distinctly high levels of nitrogen and phosphorus from fertilizers and pesticides, and the radionuclide fallout from nuclear weapons also stand as global markers of the Anthropocene. A vast reshaping of coastal sedimentation and widespread species extinction might also be used in the distant geological future to mark the epoch, the scientists say. The starting date for the Anthropocene is still under review, but may be somewhere around 1950 C.E., at the start of the nuclear age and the mid 20th century acceleration of population growth, industrialization, and mineral and energy use. "Not only would this represent the first instance of a new epoch having been witnessed firsthand by advanced human societies, it would be one stemming from the consequences of their own doing," the authors write.