WHAT IS GEOLOGIC TIME?

HOW ARE THE

EONS

FURTHER SUBDIVIDED?

WHAT IS THE MEGHALAYAN AGE?

Source: Encyclopaedia Britannica, International Commission on Stratigraphy Research: Atul Thakur, Graphic: Karthic R Iyer

Stalagmites on the floors of the Krem Mawmluh caves in Meghalaya provide evidence of a distinct stage in the geologic classification of Earth ’s age , so say researchers who have termed this most current timespan in the planet’s 4.6 bnyear-old history the ‘Meghalayan Age’. These slices of time chart key events in the story of evolution of our planet and the life forms that occupy it. A look...The time recorded by written history charting important events of human civilisation is miniscule as compared to the overall history of the planet that is known as geologic time. The enumeration by geologists, palaeontologists, and other Earth scientists of geologic time units is done by the study of rock layers and the fossil forms trapped in that. Scientists determine the time when they were formed to understand Earth at that time. Broadly, each geologic timespan is divided into different units based on the occurrence in their duration of unique plants and animals as well as major evolutionary or extinction events. The longest unit of this geologic time scale is known as eon. Earth’s total age is divided into three formal and one informal eon.The eon, a very large span of time, is subdivided into eras that are further broken down into periods. The periods are divided into epochs that are further divided into ages. These divisions are done by studying the rocks formed during these periods and the fossil forms trapped therein. The Phanerozoic Eon is divided into the Palaeozoic (541m to 252m years ago), Mesozoic (252m to 66m years ago), and Cenozoic (66m years ago to the present) eras, which are divided into twelve periods.Based on the difference between the animal and plant forms originating in them, geologic periods are further divided into series (epoch) that are again divided into stage/ages. The Quaternary period is divided into two series (epochs) —Pleistocene and Holocene. The Holocene series that covers approximately 11,700 years in Earth’s history is coincident with the late Stone Age. The Holocene series is divided into three stages of which the Meghalayan Age is the last. It starts at 4,200 years ago when agricultural societies around the world experienced an abrupt and critical mega-drought that resulted in the collapse of civilisations and prompted human migrations in Egypt, Greece, Syria, Palestine, Mesopotamia, the Indus Valley, and the Yangtze River Valley.