Issue
About 4,000 to 5,000 years ago, a severe drought crippled countries of Southeast Asia forcing a shift in human settlement patterns of the area.
Background
Researchers have now told the reason behind this mega-drought. By studying the mineral deposits of caves in Vietnam they point to a connection between the end of the Green Sahara and this mega-drought.
Details
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The team collected stalagmite samples from the caves in Laos and examined the oxygen, carbon isotopes and trace metals.
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They also conducted different modelling and paleoclimate experiments. The data suggested that during this period the Sahara started losing its vegetation.
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The reduced plant growth led to increased airborne dust which cooled the Indian Ocean, shifted the atmospheric circulation patterns and caused a condition similar to today’s El Niño events.
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This ultimately led to a large reduction in monsoon moisture across Southeast Asia that lasted more than 1,000 years.
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Previous studies have shown that this demise of the Green Sahara also caused the collapse of the Akkadian Empire of Mesopotamia and the de-urbanisation of the Indus Valley Civilization.
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This mega-drought period also brought about many lifestyle changes in the mainland Southeast Asian countries of Myanmar, Thailand, Laos, Cambodia, and Vietnam.
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The first appearance of cultivated cereals - millet in central Thailand and rice in northeast Thailand were during this period. It also introduced the nucleated village agrarian lifeway.
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Studies of ancient DNA sequencing of human genomes have also pointed to population changes in mainland Southeast Asia about 4,000 years ago leading to some emigration in the region.
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Results from this work could help us better understand, to varying degrees, the observed societal shifts across many parts of the tropics and extra-tropics.