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Does evidence buried by a super-volcano redraw the map of human migration?


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Local workers sift through Paleolithic deposits at the Billa Surgam Caves of Andhra Pradesh, first excavated in the 19th century. Now, as then, aggressive bees occasionally threaten the excavation. The caves were once thought to hold Upper Paleolithic deposits--a conclusion that an international team of archaeologists is questioning. (Samir S. Patel)

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One of the project leaders in the Jurreru Valley, Mike Petraglia examines Paleolithic finds with local villagers, who have taken an interest in the prehistory on their doorsteps. (Samir S. Patel)

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At the excavation trench called Locality 22, archaeologist Janardhana Bora (right) supervises the careful removal of stone artifacts. The white line at the base of the trench wall (top left) is ash from the super-eruption of the Toba Volcano 74,000 years ago. (Samir S. Patel)

The great alchemy of prehistoric archaeology is the way it conjures our story--of modern humans, that is--from bits of stone and bone. But the tale of our evolution and migration to every corner of the planet is filled with gaps and guesswork. Scholars have been trying for decades to make sense of it. Much of their focus for the Middle and Upper Paleolithic eras, from roughly 250,000 to 30,000 years ago, has been on Africa, Europe, and the Levant (eastern Mediterranean). University of Oxford archaeologist Mike Petraglia sees an injustice there, which he and a diverse team of researchers from three continents are working to rectify. Specifically, they believe that India deserves a central place in our understanding of the Paleolithic. Their evidence suggests that modern humans arrived there rather early and thrived under some unusually grim conditions.

The missing chapter of our story that they have uncovered in the state of Andhra Pradesh has no clear beginning, but it has a rare bookmark, a hazy horizon of fine grit that marks what may be the most important event in human history. And there--around 74,000 years ago, well before Homo sapiens are thought to have arrived in India--is where we start.

The Jurreru Valley is wide on the bottom and steep on the sides. Now dammed, in the Middle Paleolithic its river lazily meandered and fed shallow lakes during the monsoon. The water attracted people--who they were is a critical matter of debate--and funneled them through the landscape. They hunted, gathered, and made tools from stone eroding out of the valley's south side. But one day 74,000 years ago their lives took a dramatic turn. A low, distant rumble rolled in from the south, followed hours later by horizon-spanning clouds stacked like thunderheads. Day turned darker than night, a chill hit the air, and there began a blizzard of fine, abrasive particles--ash from 1,700 miles southeast on the Indonesian island of Sumatra. One of the most explosive events known, the Toba Volcano spewed 670 cubic miles of ash 25 miles into the atmosphere. In India there was nowhere to hide. Four inches of the stuff blanketed the subcontinent. The eruption also cast sulfur into the stratosphere, forming an aerosol that scattered sunlight. Some climatologists believe this touched off a thousand-year cold snap, and geneticists say humans underwent a drastic population drop, known as a bottleneck, some time in the Middle Paleolithic. A popular theory puts the two together; Toba almost wiped us out. Pity the poor people of Jurreru. Or should we?

Samir S. Patel is a senior editor at ARCHAEOLOGY.

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