Ancient megadrought may explain civilization’s ‘missing millennia’ in Southeast Asia

A megadrought that lasted more than 1000 years may have plagued Southeast Asia 5000 years ago, setting up dramatic shifts in regional civilizations, suggests a new study of cave rocks in northern Laos. The researchers believe the drought began when the drying of the distant Sahara Desert disrupted monsoon rains and triggered droughts throughout the rest of Asia and Africa.

For years, archaeologists studying mainland Southeast Asia—an area encompassing modern-day Cambodia, Laos, Myanmar, Malaysia, Thailand, and Vietnam—have been puzzled by what they call “the missing millennia,” a period from roughly 6000 to 4000 years ago with little evidence of human settlements. University of Pennsylvania archaeologist Joyce White, a co-author on the new paper, says she and others long thought this was because researchers hadn’t yet pinpointed where people of the era lived. Now, she believes the settlements could be missing because a megadrought devastated their populations and drove them to find water elsewhere.

To re-create the climate of that time, White and her colleagues investigated stalagmites in Tham Doun Mai, a cave in northern Laos. Stalagmites are tapering pillars of rock that rise from the floors of caves; they slowly grow taller as mineral-rich water drips from cave ceilings—often after rainfall. By analyzing the content of the slowly deposited rock, researchers can gauge not only the age of the rock, but also how wet it was at the time.

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