Volcanoes in Ethiopia Shook Up Early Human Evolution

Lightning might have jumpstarted Frankenstein, but volcanic activity set our earliest relatives on their evolutionary path.

Dramatic and rapid changes from volcanic activity in Ethiopia appear to have set the stage for the emergence of Homo sapiens around 200,000 years ago. The first known fossil evidence for our species was unearthed there, where explosive volcanic activity was dramatically changing the landscape and environment, according to new research published in the journal Nature Communications.

"Pyroclastic flows -- hot currents of gas, ash and rock -- would have inundated large tracts of the rift floor while ash and pumice fallout from larger plumes are likely to have covered regions to at least 100 kilometers (62 miles) from the vent," lead author William Hutchison of the University of Oxford's Department of Earth Sciences told Seeker.

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While all of this was going on, the earliest-known members of our species were not very far away. The fossils from the Omo Kibish rock formation of southern Ethiopia date to 195,000 years ago. These early humans likely viewed the eruptions from a safe enough distance -- but their presence in the region as the volcanic activity took place seems to be too coincidental to ignore.

Hutchison said that the volcano eruptions occurred along the East African Rift System, which is a still-active continental rift where Africa is slowly being pulled apart. One segment runs through Ethiopia, where a population of around 10 million people live alongside it.

As the continent gradually pulls apart, Earth's crust along the rift is extended and thinned, allowing molten rock (magma) to rise.

Hutchison and his team reconstructed the eruptive history of a 124-mile-long segment of the rift in Ethiopia by studying the Aluto and Corbetti volcanoes there. The researchers used two techniques, argon isotopes and radiocarbon analysis, to determine the dates of erupted rocks. They also analyzed the sizes of eruptions along the rift over time.

"We suggest that an increased flux of melt from the mantle into the crust generated the large magma chambers that over-pressured and erupted 320,000–170,000 years ago," Hutchison said. "These events are called flare-ups and have been identified before in other rift zones such as the Taupo Volcanic Zone in New Zealand."

Ancestors of our species and other members of the human family tree collectively known as "hominins," as well as other animals, were already in the region, so there could have been sudden devastation as when Italy's Mount Vesuvius erupted and killed nearly everyone in its path.

"Major volcanic eruptions and the environmental devastation that followed might have greatly reduced hominin populations living in the rift zone," Hutchison said. "The eruptions themselves would have made certain sections of the rift uninhabitable, potentially for many thousands of years. These mechanisms provide a means of reducing and isolating certain populations which might have promoted human adaptation and evolution at this time."

"This suggests," he added, "that our earliest ancestors not only had to deal with changing climate but also (with) the environmental devastation caused by major explosive eruptions."

Earlier research supports that the region was heavily populated with hominins long before our species emerged on the scene. Yohannes Haile-Selassie and Denise Su of the Cleveland Museum of Natural History said "more than one species of early hominin co-existed during Lucy's time" starting at about 3.8 million years ago. Lucy (Australopithecus afarensis), they explained, "was the only potential human ancestor species that roamed in what is now the Afar region of Ethiopia."

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Hutchison even suspects that the most direct ancestors of the first Homo sapiens could be the native Ethiopians who live alongside the volcanic rift system today.

Hutchison and his team next plan to examine how the volcanic eruptions might have closed down rift migration corridors once used by the early humans, and for how long.

Photo: Erta Ale, the most active volcano in Ethiopia. New research on volcanoes that are part of the same rift system in Ethiopia finds that their activity coincides with the arrival of the first humans in the area.