Geologists have officially classified the past 4,200 years as a distinct age in time.

Following years of research, the International Commission on Stratigraphy, which is responsible for standardizing the Geologic Time Scale, has declared the past 4,200 years as the “Late Holocene Meghalayan Age.” The new classification is named after a specific rock formation found in a cave in northeast India.

The geologists say the new age began with a worldwide drought that lasted about 200 years and forced the collapse and migration of several civilizations. They say evidence of the drought has been found on all seven continents.

The organization also approved two other ages, the “Middle Holocene Northgrippian Age” and the “Early Holocene Greenlandian Age,” which began about 8,300 and 11,700 years ago, respectively. Both of these ages are named after specific ice cores found in Greenland.

All three ages comprise the “Holocene Epoch,” which began at the end of the last Ice Age and have been characterized by a wealth of sediment found on the sea floor and of the mineral calcite found in caves.

The stages of the Geologic Time Scale are determined by layers of sedimentary rock that have accumulated over time and offer a record of different eras.