After years of debate, the International Chronostratigraphic Chart has officially been revised. What does that mean, exactly? Our current point in Earth's geological timeline has been updated so that we're now living in the Meghalayan age, which kicked off 4,200 years ago with a catastrophic two-century drought that destroyed several civilizations.

The Geologic Time Scale tracks the history of our planet as a series of subdivided units of time. These are observed as stark changes in the geologic record, brought about by changes in climate, continental shifts, or cataclysms like volcanic eruptions or asteroid impacts. We're currently living in the Holocene epoch, which began 11,700 years ago at the end of the last ice age.

Epochs are usually divided into smaller periods called ages or stages, and while the Holocene has had some informal ones for a while now, the International Commission on Stratigraphy (ICS) has just made three of them official: the Greenlandian, the Northgrippian and the Meghalayan.

The Greenlandian age begins 11,700 years ago, when the Pleistocene epoch first gave way to the Holocene as the warming planet exited the ice age. The Northgrippian kicked off 8,300 years ago, and finally the Meghalayan began some 4,200 years ago. Unfortunately, the first 200 years of this current age were marked by a devastating drought, which rocked established human civilizations in Egypt, Greece, Syria, Palestine, Mesopotamia, the Indus Valley and the Yangtze River Valley.

The fact that the beginning of this age coincides with a cultural shift caused by a global climate event makes it unique, according to Stanley Finney, Secretary General of the International Union of Geological Sciences.

These start dates aren't chosen at random. Before they can be officially ratified, the ICS needs to find clear signs in the strata (rock layers) of the events that triggered the changes. Geologists say they've found evidence in sediments from the sea floor, lake beds, glacial ice and in stalactites and stalacmites from around the world. As specific examples, Greenland ice cores have been preserved that represent the beginnings of the Greenlandian and Northgrippian ages, while a slice of stalactite from a cave in India defines the start of the Meghalayan.

The decision isn't without its controversy, though. According to the BBC, some scientists argue that the move is a little premature, and hasn't been properly debated yet. Another key problem is that it might be stepping on the toes of a widespread debate already underway in the geological world, regarding the Anthropocene.

For a few years now, some scientists have argued that human activity has had such a huge impact on the planet that it may warrant the declaration of a new geological epoch, tentatively dubbed the Anthropocene. The "golden spike" that signals this change has been suggested to date back to the early 1950s, evident in the geological record as plastics, radionuclide fallout from nuclear testing, and increased carbon from fossil fuel use.

Interestingly though, the ICS seems to have left room for the Anthropocene in the revised chart. While the beginnings of the Greenlandian and Northgrippian ages are measured as "b2k" (before the year 2000), the Meghalayan apparently begins 4,200 years before 1950 – the year of the supposed golden spike that marks the beginning of this new human-induced epoch.

Source: International Commission on Stratigraphy [1],[2]

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