Despite its largely hyper-arid and inhospitable climate today, the Arabian Peninsula is emerging as an important area for investigating human dispersal activity.
Yesterday, archaeologists found 300,000-year-old stone tools in Saudi Arabia, at a time when the Arabian Peninsula was a grassland dotted with lakes.
The unearthed stone tools in the Nefud Desert indicate that members of our ancestors had ventured beyond the familiar borders of Africa and the Levant sometime between 300,000 and 500,000 years ago. And according to climate data captured in the bones of animals found at the site, the environment they moved into may not have been that different from the one they left behind in East Africa.
The things they left behind
Archaeologist Patrick Roberts of the Max Planck Institute for the Science of Human History and his colleagues recently discovered a handful of stone tools in a sandy layer of soil beneath the dry traces of a shallow Pleistocene lake at Ti’s al Ghadah, in the Nefud Desert of northern Saudi Arabia. The soil layer dated to between 300,000 and 500,000 years ago, and it also contained fossilized remains of grazing animals, water birds, and predators like hyena and jaguar. Many of the bones seem to bear the marks of butchering by tool-wielding humans.
The tools—six sharp brown chert flakes and a scraper are the oldest radiometrically dated artifacts in the Arabian Peninsula, edging out the previous contender by 100,000 years.
The flakes show signs of being struck from a prepared stone core, which is a fairly advanced technique usually attributed to modern humans.
Ancient environmental records in the bones that lay alongside the long-discarded tools suggest that the Nefud was a very different place at the time.
When Arabia was green
Roberts and his colleagues used chemical signatures to reconstruct an ancient environment that looked surprisingly like the humid savanna of modern East Africa.
At Ti’s al Ghadah, tooth enamel from 21 fossilized herbivores of different species contained carbon-13 ratios that almost exactly matched a diet of C4 grasses. That suggests a large swath of open grassland around the shores of the vanished shallow lake.
That’s a very different landscape from today’s dunes of reddish sand, and the ratios of oxygen-18 to other oxygen isotopes in the tooth enamel of the Ti’s al Ghadah fossils suggest a much wetter climate in the Nefud of 300,000 years ago.
Those ratios line up with climate models that suggest a wetter, more hospitable environment in Arabia, courtesy of a shift in Africa’s monsoons during periods of warmer global climate called interglacials. They also help make sense of the collection of animals found at the site: elephants, oryx, hartebeest, and others that would have thrived in a savanna. That means that, during the early pulses of migration out of Africa, the Middle Pleistocene pioneers wouldn’t have faced the challenge of adapting to life in today’s hot, arid desert.
Ancient climate records—etched in sediments at the bottom of lakes and in layers of mineral deposits in caves—suggest that the Arabian Peninsula enjoyed several phases of milder, wetter climate during two million years of our predecessors’ movements through the region. But between those phases, the region dried up and the desert closed in again.