Geologists have defined the last 4,200 years as a new chapter in Earth’s history, the Meghalayan Age. This age began at the time when agricultural societies around the world “experienced an abrupt and critical mega-drought and cooling”, the International Union of Geological Sciences has announced.

The 4.6-billion-year existence of Earth time is divided by geologists into eon, era, period, epoch and age. The Meghalayan Age is part of a longer period known as the Holocene Epoch, which began about 11,700 years ago.

An international team of researchers collected sediments from across the world, including a stalagmite from a cave in Meghalaya, to define the latest age in Earth’s history. The Mawmluh cave in Meghalaya is located at an elevation of 1,290 metres and is among the top ten longest and deepest caves in India. The stalagmite collected from here has shown that the conditions in the cave were suitable for preserving chemical signs of the transition in ages, according to the Hindustan Times.

“Agriculture-based societies developed in several regions after the end of the last Ice Age, before a 200-year climatic event affected agricultural societies, forcing the collapse of civilizations and migrations and regenerations in Egypt, Greece, Syria, Palestine, Mesopotamia, the Indus Valley, and the Yangtze River Valley,” the International Union of Geological Sciences said. The climatic event, a destructive drought, was likely triggered by a shift in oceans and the atmospheric circulation, according to BBC.

Evidence of this period has been found on all seven continents, said the International Union of Geological Sciences, which ratified the proposal for the Meghalayan Age sent by the International Commission on Stratigraphy.

This commission is responsible for the standardising the geological time scale. It proposed that three stages be introduced in the Holocene Epoch – the early Greenlandian Age, which began about 11,700 years ago, the middle Northgrippian Age, which began about 8,300 years ago, and the late Meghalayan Age.

“The commission then forwarded these proposals to its parent body, the IUGS, for consideration, and the executive committee of IUGS voted unanimously to ratify them,” the International Union of Geological Sciences said.

“The Meghalayan Age is unique among the many intervals of the Geologic Time Scale in that its beginning coincides with a cultural event produced by a global climatic event,” Dr Stanley Finney, secretary general of the International Union of Geological Sciences, said.

“The convergence of stratigraphy and human cultural evolution is extraordinary,” said Martin Head, geologist and chairperson of the International Subcommission on Quarternary Stratigraphy.

“Units of the Geologic Time Scale are based on sedimentary strata that have accumulated over time and contain within them sediment types, fossils and chemical isotopes that record the passage of time as well as the physical and biological events that produced them,” the International Union of Geological Sciences said.

“The three new ages of the Holocene Epoch are represented by a wealth of sediment that accumulated worldwide on the sea floor, on lake bottoms, as glacial ice, and as calcite layers in stalactites and stalagmites.”