Volcanoes might have forced early humans out of Africa, altering the course of our evolution

A surge in volcanic eruptions between 320,000 and 170,000 years ago appears to have changed the course of human evolution. Scientists say this pulse of activity along the East African Rift System would have drastically altered the landscape and environment for the Homo sapiens arriving in Ethiopia 200,000 years ago.

Led by a team from the University of Oxford, scientists were looking at a specific stretch of the East African Rift System – the Ethiopian Rift Valley. This area represents the longest record of humans living alongside volcanoes anywhere on Earth, yet our understanding of its eruptive history is poor.

To get a better insight into early volcanism along a 200km-segment of the rift system, the team used argon isotopes and radiocarbon dating in order to create an eruptive history of the area. They compared the data to that of two other rift volcanoes.

Their findings, published in Nature Communications, showed a large pulse in explosive volcanism for 15,000 years, beginning 320,000 years ago. The rate of eruptions in this section was five times higher than the average rate for the rest of the rift. The increase in volcanic activity was likely due to increased magma movement from the mantle to the crust, they said.

Such a surge in volcanic activity would have had a big impact on early humans in the region at the time. And the mid-point of the surge coincided with a key moment in the evolution of humans – the arrival of Homo sapiens in Ethiopia.

"The Middle Pleistocene of Ethiopia spans a key juncture in hominin evolution, represented by the arrival of anatomically modern humans (ie. our species Homo sapiens) in the region around 200,000 years ago," the team wrote. "Although the evolutionary stimulus at this time remains uncertain, current evidence overwhelming suggests that all major events in hominin evolution occurred in East Africa."

Researchers say environmental factors are often looked at when it comes to the evolution of early humans, with periods of climate change having a huge role in their development. This surge in volcanic activity at the dawn of our species, they argue, would have had a major impact on the environment – therefore us.

"While attempts to understand the links between past environmental change and human evolution have stimulated considerable research into African paleoclimate, comparatively little attention has been paid to the role of explosive volcanism in influencing rift habitability," they said.

"Ash, acidic gases and aerosol released from such events would have affected rift lakes and vegetation causing a cascade of environmental disruption, remodelling the landscapes and resources on which hominins depended."

They said every volcanic pulse would have resulted in "significant environmental change" and that volcanism could have ultimately been responsible for pushing early humans out of Africa.

"Pulses of explosive volcanism may typify the East African Rift; each of these would cause significant environmental change, and should not be overlooked as drivers of the population bottlenecks seen in hominin records in East African, as well as a potential 'push' factor for human dispersal within and out of Africa."