Many evolutionary studies have suggested Africa was the birthplace of the first Homo sapiens but there has been much debate about when humankind began expanding into other regions.
According to the Geological Society of America (GSA), two main theories exist: “In one scenario, human populations expanded rapidly from Africa to southern Asia via the coastlines of Arabia approximately 50,000 to 60,000 years ago.
“Another model suggests that dispersal into the Arabian interior began much earlier (approximately 75,000 to 130,000 years ago) during multiple phases, when increased rainfall provided sufficient freshwater to support expanding populations.”
A research paper published in the GSA’s journal Geology earlier this year has outlined new evidence found at a quarry in support of the latter theory.
In a blog post about his research, lead author of the paper, Ash Parton, explained that a deep, approximately 42m sequence of alluvial fan deposits – fan-shaped deposits of gravel, sand and/or other sediment that have been transported by flowing water – had been exposed by excavation at the Al Sibetah quarry, located in Al Ain in the United Arab Emirates.
“These ancient river channel and soil sediments comprised the biggest record of major climate changes from anywhere in the peninsula, and provided evidence of multiple periods of increased rainfall,” he said.
More migration opportunities
It was previously believed that human migration would only have been possible during “interglacials” – the periods between ice ages when global temperatures would become warmer – due to the fact that the Arabian climate during the intervening “glacial” periods would have been too arid for humans to survive in. It was thought that these opportunities for migration had only occurred about once every 100,000 years.
However, the quarry discovery indicated that wet periods had been far more frequent, occurring approximately every 23,000 years, and that they had been triggered by monsoon events rather than more sporadic global ice volume changes.
“During these [wet] periods, expansive river systems surrounded by verdant savannah grasslands and trees connected the mountains and the coast, potentially acting as vast green corridors through which early human populations could move,” Parton said.
“Importantly, the findings suggest that there were numerous windows for the dispersal of human populations out of Africa, and that demographic mobility was not restricted to interglacial periods every ~100,000 years.”
Parton’s research paper is available via www.palaeodeserts.com