Humans have left tangible evidence of their activities throughout history, but have those activities had a geologic impact? And if so, how would this affect the field of geology? These are the questions explored by Nicola Davison in this long-form article written for The Guardian and published on May 30, 2019. As the article explains, to help conceptualize planetary changes stretching back billions of years, stratigraphers (geologists who study rock layers) created an official timeline called the International Chronostratigraphic Chart that divides the Earth's history into different geologic units. According to this chart, human history falls within the Holocene epoch, but in 2000 atmospheric chemist Paul Crutzen began asserting that humans had become the leading geologic force, thereby making the term Holocene obsolete. Although many geologists initially dismissed the idea of this new epoch, which Crutzen labeled the Anthropocene, by 2008 the notion had taken hold to the point that stratigrapher Jan Zalasiewicz formed a working group of geologists and other scientists to examine the geologic evidence for the Anthropocene and to determine how it should be defined. This in-depth article provides an excellent overview of the context and debate surrounding this emergent scientific concept.