Monsoon deluges turned ancient Sahara green | Science News

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Monsoon deluges turned ancient Sahara green

Leaf-wax measurements used to reconstruct 25,000 years of rainfall

4:37pm, January 18, 2017
Sahara desert

RAIN OUT  Rainier conditions than previously thought turned the Sahara Desert into grasslands, lakes and rivers from 11,000 to 5,000 years ago, a new study finds. A brief return to aridity around 8,000 years ago set the stage for cattle herders to spread across North Africa, researchers suspect.

Thousands of years ago, it didn’t just rain on the Sahara Desert. It poured.

Grasslands, trees, lakes and rivers once covered North Africa’s now arid, unforgiving landscape. From about 11,000 to 5,000 years ago, much higher rainfall rates than previously estimated created that “Green Sahara,” say geologist Jessica Tierney of the University of Arizona in Tucson and her colleagues. Extensive ground cover, combined with reductions of airborne dust, intensified water evaporation into the atmosphere, leading to monsoonlike conditions, the scientists report January 18 in Science Advances.

Tierney’s team reconstructed western Saharan rainfall patterns over the last 25,000 years. Estimates relied on measurements of forms of carbon and hydrogen in leaf wax recovered from ocean sediment cores collected off the Sahara’s west coast. Concentrations of these substances

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