The Meghalayan Age

Nearly 5000 years ago, a tremendous global drought devastated multiple ancient agricultural societies, including China, Greece, Egypt, Mesopotamia, Syria, Palestine, the Indus Valley, and the Yangtze River Valley. Now, scientists have classified that monumental event and its impact as the onset of a geological age, in addition to determining two other stages that preceded it; They have named these ages the Meghalayan, the Northgrippian, and the Greenlandian.

Geologists divide the 4.54 billion year history of Earth into portions of time. Each section reflects some significant happenings in a global context, such as the separation of continents or critical shifts in climate.

Currently, we are in the Holocene epoch. This epoch represents the occurrences of the last 11,700, since the last ice age. However, according to the International Commission on Stratigraphy (ICS), this epoch can be subdivided into periods of time known as ages. The ICS is the official governing body responsible for outlining the segments of time and, in a statement released on July 13, they determined that there are three stages in the Holocene, which stand for the epoch’s upper, lower and middle phases.

The ICS classified the oldest phase as the Greenlandian, beginning at the exit of the ice age, and ending at the onset of the middle phase. This phase is now known as the Northgrippian. It started 8,300 years ago and runs up until the start of the Meghalayan. The start of this age was marked by an sudden cooling, credited to the extensive volumes of freshwater from melting glaciers in Canada that flooded into the North Atlantic, thus disrupting ocean currents.

The youngest age is the Meghalayan age. Marked by a tremendous drought with effects lasting nearly two centuries, it runs from 4,200 years ago to the present. The drought was most likely a consequence of shifts in the oceans and atmospheric circulation.

The ICS bases their classifications on indicators in Earth’s rock record. That is: the segment of time has to be associated with a rock or sediment type that is unambiguous. For example, the transition from the Cretaceous Period to the Palaeogene was determined by the traces of iridium that were left throughout the Earth’s sediment when an asteroid drove the dinosaurs to extinction 66 million years ago.

This indicator was found for the Meghalayan age in a rock sample from the northeastern state of Meghalaya, India, for which the age is named after. Geologists analyzed stalagmite, the type of rock formation that rises from the floor of a cave due to material deposited on the floor, growing on the ground of a cave in Mawmluh Cave. They found that each layer had different oxygen isotopes. Prof Mike Walker of the University of Wales, UK, explained that “The isotopic shift reflects a 20-30% decrease in monsoon rainfall.” Walker led the team of scientists that proposed the division of the Holocene. Evidence for the Meghalayan “has been found on all seven continents,” say scientists in the ICS press release.

The evidence for the other two phases of the Holocene was found in the ice cores from Greenland. Further evidence for all three stages was found in sediment that accrued on the seafloor worldwide and in calcite layers in other stalagmites.

Stanley Finney, the Secretary-General of the International Union of Geological Sciences (IUGS), says that The Meghalayan Age is considered unique amongst the intervals in the Geologic Time Scale because its onset depicts a global cultural event provoked by a global climatic event. In other words, the restoration of destroyed agricultural societies was sparked by the massive drought that devastated the first 200 years of this stage.

The decision to divide and categorize the Holocene has already received some backlash from scientists around the world. Some say that the decision is hasty and the official classification requires further discussion. Others argue that the climate shifts used to justify the new ages were not global in their impact. Scientists are also concerned with the fact that the decision was made while there is still active debate regarding new geological segments of time specifically indicating human influences on Earth. This new segment is tentatively referred to as the Anthropocene.

A definite answer to all these disputes is to come sometime in the future. In the meantime, we can celebrate this new chapter. Welcome to the Meghalayan age!