When Arabia was green: lush grasslands helped early man make leap out of Africa

The sands of the Empty Quarter may hide the secrets of how mankind conquered the Earth, new research is showing

Michael Petraglia, professor of human evolution and prehistory at the University of Oxford’s School of Archaeology, at an ancient buried lake in the Nefud Desert, northern Saudi Arabia. Courtesy Michael Petraglia
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A prehistory professor has unearthed evidence that the Arabian Peninsula played a pivotal role in the evolution and migration of our species across the planet, and that the arid desert was once a lush green habitable landscape.

Michael Petraglia is no stranger to the hot, dusty and physically demanding business of unearthing the secrets of our distant past in some of the more inhospitable places on Earth.

So it came as a pleasant surprise in 2001 for the professor of human evolution and prehistory at the University of Oxford’s School of Archaeology to make one of his more unexpected discoveries in the air-conditioned comfort of the library at the National Museum of Saudi Arabia.

What he found, meticulously recorded in an archaeology journal almost completely unknown outside Saudi Arabia, were fascinating clues to the area’s prehistoric past that would trigger a dramatic reappraisal of the role played by the Arabian Peninsula in the migration of the first humans out of Africa.

As Professor Petraglia turned the pages of Atlal, reviewing the findings of the Comprehensive Archaeological Survey ordered by the Saudi government in the 1970s, the seed of an idea was planted that by 2012 would grow into an international project.

“Arabia had been completely underplayed in the story of human migrations out of Africa,” says Prof Petraglia, reflecting on the first three years of the five-year Palaeodeserts Project, on which he is the principal investigator.

With another two years of the project left to run, “the progress has been beyond my expectations”, he says. “I don’t know if I should say this myself, but we’re transforming the prehistory of Arabia.”

Launched as a five-year collaboration between the Saudi Commission for Tourism and Antiquities and Oxford University’s School of Archaeology, the Palaeodeserts Project has so far involved more than 30 scholars from a dozen institutions and seven countries.

They work in a range of disciplines including palaeontology, geography, geochronology, animal and human genetics, archaeology, rock art studies and linguistics. It was a measure of the international significance of the work that it attracted a €2.4 million (Dh9.9m) grant from the European Research Council.

The picture emerging from the sands of time is both incredibly complex in its scope and yet astonishingly simple in its implications.

Once upon a time, vast and now arid parts of Arabia were lush, green landscapes, irrigated by lakes and rivers and populated by large mammals, such as big cats, elephants and hippos, of a kind we now associate only with Africa.

“And today,” says Prof Petraglia, with contagious enthusiasm, “this is the Empty Quarter”. “Just imagine.”

One of many such sites is at Mundafan, in the south-west of Saudi Arabia at the junction between the Asir and Tuwayq mountains and the Rub’ Al Khali desert, or Empty Quarter.

To the untutored eye all that can be seen are the dunes of a typical, windblown Arabian desert. In fact, as extensive research has now shown, this was once the site of a large freshwater lake – a finding that has been repeated at locations across the Arabian peninsula.

Such dramatic, climate-driven transformations played a sensational role in the development of our species. As if by a process of osmosis, the lush conditions of Arabia, which came and went in cycles of thousands of years at a time over a period of a million years, drew early humans eastward from Africa.

This was the late Pleistocene period, which ended about 12,000 years ago, during which Homo sapiens – the “wise man” – out-competed all other species of humans to became the dominant life form on Earth.

And thanks to the project, we now know that: “Arabia was a key stepping stone out of Africa”, says Prof Petraglia. It is a role that has, until now, been largely neglected.

Accepted wisdom that well preserved archaeological sites were unlikely to be found in deserts proved unfounded – in fact, the opposite has been shown to be true.

“Beneath the sands there are many secrets,” says Petraglia.

“The wonderful thing is that many of these sites are remote and inaccessible, which makes them logistically very hard to work in, but it means they have remained very well protected.”

One such site is at Jabal Umm Sanman, in the Great Nafud Desert, which has yielded a treasury of rock art, epigraphy and other evidence of human habitation along the shores of a now-vanished 20km-long lake, dating back about 8,000 years. This is one of 11 sites in Saudi Arabia currently under consideration for inclusion on UNESCO’s World Heritage List.

Such discoveries, says Prof Petraglia, show that far from being an archaeological wasteland: “Arabia is a beautiful laboratory for examining cultural and demographic change relative to climate change”.

For Prof Petraglia, the story began in 2000, when he was a research associate at the Smithsonian in Washington. A delegation from the Saudi Arabian Ministry of Education visited the institution for the launch of Written in Stone, a joint website dedicated to some of the 9,000 examples of ancient rock inscriptions found in the country.

“I told them I was interested in migrations out of Africa and that I was comparing India to Africa. They said, ‘Well, isn’t Saudi Arabia a logical place to be working?’. I thought, ‘Absolutely’, and put in for a Fulbright grant.”

In 2001 Petraglia spent several months in Saudi Arabia: “And I was just blown away”. Until then, he had never heard of the huge national archaeological survey carried out in the 1980s, which had been reported in Atlal but had not become part of the international scientific literature.

While in the country, he was able to visit three or four sites. Among them was Dawadmi, in the very centre of the Arabian peninsula, where, he says: “I saw all these amazing and well preserved stone tools, distributed literally over kilometres.”

With artefacts spread over 200 kilometres, the Dawadmi site turned out to be one of the largest in the world for stone tools made by early man.

The Palaeodeserts Project marked its halfway point last April with a conference in Oxford, the title of which summed up the new perception of the role of the region in shaping human destiny: “Green Arabia: Human Prehistory at the Crossroads of Continents”.

“We called it Green Arabia because many times in the past Arabia was green, with grasslands, wooded landscapes, rivers and lakes,” says Prof Petraglia.

“With that title we were trying to break down the stereotypical image of Arabia as just this barren, desolate, hyper-arid place, because it is so much more interesting than that.”

One of the key lessons that has emerged from the project, with much resonance for our times, is that climate change played the central role in determining the early fate of our species.

“We now have evidence of dramatic swings through time between wet and dry, a repeated cycle,” says Prof Petraglia.

“We have aridity and deserts forming, but that’s followed by humidity and lakes and rivers, which drew populations across the Sahara and into Arabia. The big question is what happened to those populations when things got bad?”

Part of the answer is that the changing environment pushed whole populations out again. Some headed east, ultimately to populate other areas of the Earth for the first time, while some sought sanctuary in what were then more favourable environmental zones, such as in southern Arabia or along the Gulf. Now, of course, the region is in a dry period, but Prof Petraglia says: “The prediction would have to be that, in the future, that wet periods will reappear again across the Sahara and Arabia.”

“This is a natural cycle that Earth’s climate has been going through for hundreds of thousands of years.”

Predicting exactly when rivers might once again flow through the Empty Quarter is “very difficult”, and made doubly so by the very creatures whose global distribution and dominance was made possible by that natural cycle in the first place – us.

“People are influencing these processes nowadays, which of course makes all the difference.”

The immediate future of the project lies in the development of a Green Arabia Research Centre in Riyadh, announced last year by Prince Sultan bin Salman Al Saud, president of the Saudi Commission for Tourism & Antiquities.

Prof Petraglia’s thoughts are already turning to other regions of Arabia, which he believes could supply additional pieces of the prehistoric jigsaw puzzle.

“Given the opportunity, we would apply the same international, interdisciplinary and collaborative approach to the archaeological record of the Gulf, including in the UAE,” he says.

The Arabian Gulf has a well-known archaeological record, which extends back 10,000 years, but “it needs to be better understood with respect to how climate change affected populations, examining how societies changed from being hunter-gatherers to herder-hunters, and fishermen”.

Even more exciting, the sands of the Gulf could conceal an even greater treasure, he believes.

“There are now hints that the Gulf has a much deeper prehistory, extending back 100,000 years or more.

“Full-scale and detailed archaeological surveys and excavations are sorely needed.”