We may be in a new epoch. Like the humans that survived the last glacial period to move from the Pleistocene to the Holocene, modern humans may have left the Holocene to enter the brand-new Anthropocene—the "age of humans." To delineate these stretches of time, geologists must identify individual boundaries in layers of rock known as strata. If a boundary is found in rock all over the world, the International Commission on Stratigraphy (ICS) appraises it for entry in the International Chronostratigraphic Chart, which defines geologic time in terms of eons, eras, periods, epochs, and ages.
Often, these rock boundaries are caused by natural events such as ice ages and volcanic activity. The Anthropocene is not yet an official epoch, but if it becomes one, it will be defined by human activity—specifically, the significant changes we've made to the land, air, and water. The date of the epoch's start is up in the air, but it will most likely be 1945, the date of the first nuclear bomb detonation. There's another thing that's unusual about the Anthropocene beyond its human influence: geologic time is usually captured in rock, and it's too early to see human influence in the geologic record. If the ICS adds this epoch, it will be the first of its kind. Explore the science of strata with the videos below.