‘Meghalayan Age’: New chapter in earth’s history
NEWDELHI: The most recent ‘age’ in earth’s 4.54 billion year history began 4,200 years ago and has officially been designated the ‘Meghalayan Age’.
The earth’s recorded history is divided into units of eon, era, period, epoch and age, with the age being the smallest unit of geologic time. Meghalaya is now part of geologic history, as is a slice of stalagmite found in the Mawmluh cave in the northeastern state. Located at an elevation of 1,290 metres, Mawmluh cave in the Khasi hills is one of the longest and deepest in India, and conditions here suitable for preserving transition signals.
The demarcation is significant for multiple reasons. It is the first formal geological subdivision of the Holocene epoch that began 11,600 years ago and extends to the present, into three ages: Greenlandian, Northgrippian and Meghalayan.
“The onset of the Meghalayan age is marked by what is known as the 4.2 ka (thousand years) climatic event that registers as a severe drought in records from many low latitude regions, and by increases in precipitation in others, especially in the high latitudes,” Mike Walker, who heads the working group on the subdivision of the Holocene at the International Commission on Stratigraphy (ICS), the body tasked with defining the geologic time scale, said in an emailed interview.
“It is a period of increasingly unstable climate and reflects a significant reorganisation of ocean and atmosphere circulation patterns.”
Geologists examine sedimentary deposits on land, ice cores and deposits below the seafloor, for clues to when dramatic changes took place — dramatic enough to be designated as a new phase in earth’s history. Something akin to a medical examiner looking for transformative changes in the human body when it enters a new phase of life such as puberty.
The clinching marker was found in stalagmite or rock formations rising from the floor in Mawmluh cave.
Among these formations scientists have found the clearest chemical signal for a transition from the preceding Northgrippian age.
A portion of stalagmite is now a Global Boundary Stratotype Section and Points, the first formally ratified GSSP in India. These reference points have to be internationally agreed upon based on clear evidence.
This also is the first time a cultural event linked to a climatic phenomena with implications for civilisations across the globe, marks the start of a geological unit of time. The start of this age is linked to upheavals in north Africa, the Middle East and Asia. Around this time Akkadian Empire collapsed in Mesopotamia because of sudden aridification, and the Old Kingdom in Egypt was vanquished after a flurry of Nile floods,a nd the Indus Valley civilisation shifted from the urban Harappan civilisation to a rural post-urban society. These changes on the Indian subcontinent are believed to have resulted from a weakening of the Indian monsoon that precipitated drought conditions. In China, extreme dry conditions have been linked to the decay of many Neololithic cultures.
“It seems a sensible and widely welcomed subdivision within that community, and the formalisation seems to be widely regarded as a useful step, to precisely fix the meaning of the subdivisions,” said Jan Zalasiewicz, a professor at the University of Leicester who was not directly involved with the ratification.
The designation is not without controversy. Scientists have challenged the move noting that this thwarts efforts to carve out the Anthropocene epoch, that would succeed the Holocene, in recognition of the human footprint on the entire planet.
“With the ongoing discussions concerning the Anthropocene Epoch many colleagues feel that the Holocene is an outdated term and it should be removed and replaced by the Anthropocene,” Mark Maslin, at the University College London, said. “Hence the three Ages described recently are not required and are purely in place as a political means of trying to save the Holocene.”
Another point of contention is that the episodes that are used to mark the start of the stages are not truly global in scope. In the case of the Meghalayan age, Muslin said, “the mega drought only affected civilisations in the Middle East and North Africa, India and parts of China,” and leaves out “the huge civilisations that existed in the Americas and Africa and Northern Europe.”