The periodic "greening" of deserts has led humans out of Africa

Eight years ago, a colorful ancient lake in the Nevd Desert in northern Saudi Arabia caught the attention of researchers. When scientists dug up its ancient coastline, thousands of stone tools were found, and evidence that generations of Homo sapiens and their close relatives migrated inland Arabia on many occasions over the past 400,000 years, a new study says. The relevant research results have been published in Nature.

Jessica Thompson, a paleoanthropologist at Yale University who was not involved in the study, said the findings support the idea that the periodic greening of this typical hot desert played a key role in the departure of humans from Africa, while providing the strongest evidence to date that different human groups left the continent through the Sinai Peninsula.

Today, the sparsely populated Nevde Desert is full of sand dunes and slender, drought-tolerant shrubs. But previous excavations and paleoclimate modelling studies have revealed that over the past 500,000 years, short-lived, wet, warm climates have brought seasonal rainfall to the region, turning lower-lying basins into lakes and ditches into rivers, and deserts temporarily turning into lush grasslands, but turning them into sandy lands when dry weather strikes.

In 2013, scientists locked down several ancient lake beds in the western Nevde Desert, which took on unusual colors in satellite imagery. Michael Petraglia, an archaeologist at the Max Planck Institute for The Science of Human History (SHH), suspects that its marble-like sediment bands reflect several drainage as well as refill periods.

Petraglia and colleagues traveled to a location called Khall Amayshan 4 between huge sand dunes. "There are stone tools everywhere." SHH archaeologist Huw Groucutt said.

The researchers used excavators to dig on the lakebed, dating these formations and recording the stone tools associated with each formation. The results showed that the ancient lake of Khall Amayshan 4 formed and dried up 6 times. Researchers have reported that stone tools are related to five of these long-disappeared lakes, the latter dating back to 400,000 years ago, 300,000 years ago, 200,000 years ago, 100,000 years ago and 55,000 years ago. In another ancient lake in the Gyuba Oasis, about 150 kilometers east of the site, they found stone tools dating from 200,000 to 75,000 years ago.

In addition to the tools, the researchers found fossilized animal bones in many dried-up lakes, suggesting that African animals such as hippos, elephants and ostriches left Africa along this "green route" — at least during the rainy season. No human fossils have been found in the new excavations.

Groucutt said it's unclear which ancient humans left the tools behind, but the relatively rough pointed-handed axes are often thought to have come from close relatives of humans, such as Homo erectus. The researchers note that tools found in rock formations 200,000, 100,000 and 75,000 years ago are smaller and more elaborately crafted, similar to those made by humans.

The most recent tool from 55,000 years ago is very similar to the neanderthal tool. Scientists have found Neanderthal remains on the northwestern edge of the Arabian Peninsula. If these new discoveries hold true, they suggest that Neanderthals also migrated to the periodic "prairie paradise" of the Arabian Peninsula. Bunraku

Source: China Science Daily