‘Rocks equal time’: A geoscientist unpacks timescales
Steve Petsch, geosciences, writes in The Conversation about the custom of dividing and categorizing time into ages, epochs and eras, and who gets to decide. Petsch also posits where the newly named “Meghalayan” age fits in to the schema.
From "Welcome to the new Meghalayan age – here’s how it fits with the rest of Earth’s geologic history":
Scientists still continue to refine the geologic timescale. This summer brought the official naming of a new age: the Meghalayan.
Numerous climate records show that Earth faced an abrupt shift towards a cooler and drier climate 4,200 years ago. A team led by stratigrapher and climate scientist Mike Walker proposed that this was a significant and global-scale event, best represented by climate signals found in a stalagmite from Mawmluh Cave in Meghalaya state, in northeast India.
The International Commission on Stratigraphy (ICS) and its parent body, the International Union of Geological Sciences, vote on and ratify such proposals. ICS is in effect the official keeper of the geologic time scale. When a new time division is approved, as in the case of the Meghalayan, ICS sets the official description and adds that new detail to the geologic time scale.
All rocks younger than 4,200 years are now part of the Meghalayan Stage. Time since 4,200 years ago is in the Meghalayan Age. But there is a lot to unpack in these details.
As of July 2018, the Holocene – the most recent epoch of time spanning from 11,700 years ago to the present – is divided into three ages: the Greenlandian, the Northgrippian and the Meghalayan….
The global-scale climate change that defines the beginning of the Meghalayan coincides with a period of ongoing migration and collapse of many early human civilizations around the globe. For the first time, our stratigraphy has been defined at least in part by effects on human activities.