Melbourne, June 3
Few components of the world would appear as inhospitable to people because the highlands of the Tibetan Plateau, close to the Himalayas. Archaeologists have lengthy questioned when, the place and the way our ancestors started to discover and occupy these landscapes.
However proof of early human presence on the plateau has been scarce — and courting the few remaining traces has confirmed an ongoing problem.
Utilizing a not too long ago developed courting method, our analysis staff has now produced the primary stable proof for human presence on the central-southern Tibetan Plateau greater than 5,000 years in the past. Our findings are revealed at present in Science Advances.
The problem of courting floor artefact scatter The dry highlands of Tibet are thought of to be among the many final areas on Earth to have been settled by people. The excessive altitude of the area, within the shadow of Himalayan peaks greater than eight kilometres excessive, makes for excessive circumstances.
The query of the place and when the peopling of this distant area occurred has been debated amongst archaeologists. Many research have come from analysis performed at open-air areas, with considerable proof of stone device use or manufacture, equivalent to rock flakes discovered on the bottom.
These websites are known as “lithic artefact scatters”.
They’re among the many mostly preserved archaeological websites on the planet, and maintain potential to reconstruct human settlement patterns and discover numerous facets of previous human behaviour.
But it has been extraordinarily troublesome to interpret the archaeological significance and ages of those websites unambiguously. Most artefacts are constructed from stone, which makes it troublesome to find out when the instruments had been manufactured, or in the event that they had been moved after being discarded.
Artefacts on the floor are liable to erosion, and motion by wind and water, over tons of and even hundreds of years since people first produced them. Consequently, they’re usually discovered “out of context”, so a transparent relationship cannot be drawn between them and their fast environment.
Growing new strategies
To beat this limitation, our staff spent the previous a number of years within the Innsbruck OSL (optically-stimulated luminescence) courting laboratory in Austria led by Michael Meyer on the College of Innsbruck, creating a brand new method appropriate for courting historic stone instruments.
OSL courting has change into one of many essential courting strategies in archaeology and the earth sciences. It is primarily based on the buildup of vitality within the crystal construction of sand grains.
When grains are shielded from daylight, equivalent to once they’re buried, their crystal accumulates vitality resulting from low-level radiation from surrounding rocks and sediment.
This will then be measured within the laboratory, by way of managed publicity to blue and inexperienced gentle, which releases the vitality as a “luminescence sign”. The longer the grains have been buried, the extra luminescence we’ll measure from them.
As a substitute of sand for our analysis, we used an strategy referred to as “rock floor burial courting”. It is the primary ever strategy to concentrate on the sign saved beneath the floor of rock artefacts at a scatter website.
The luminescence sign constructed up inside a rock is sort of infinitely excessive, as a result of extraordinarily very long time that has handed for the reason that rock was fashioned by geological processes.
Nevertheless, as soon as a rock floor is uncovered to sunlight, equivalent to when an artefact is first produced and used, the luminescence sign is erased on the floor and simply beneath (however not on the centre). The erasure of the sign is strongest on the floor and tapers off in the direction of the centre of the artefact.
When the artefact is thrown away and turns into shielded from daylight — both from beneath, or from being lined by sediment — the sign begins to construct once more.
This results in various ranges of sign depth discovered at totally different depths beneath the artefact’s floor. We will measure this sign distribution to find out the general age and historical past of a stone artefact.
5,000 years within the shadow of Mount Everest The big potential of this new method of utilizing OSL had been proven in earlier archaeological and geological contexts, however hadn’t been rigorously examined on artefact scatter websites.
Accompanied by skilled high-altitude archaeologist Mark Aldenderfer from the College of California at Merced, and supported by mineralogist Peter Tropper from Innsbruck, we got down to take a look at the suitability of this promising methodology on the lithic artefact scatter website of Su-re, in southern Tibet.
At an elevation of 4,450 metres, in a big valley descending from the best peaks on the planet – Mount Everest and Cho’Oyu — Su-re had been identified for many years for its dense accumulation of various floor artefacts. This advised a protracted historical past of website use by people. However how lengthy?
Utilizing our courting strategy, we dated the oldest artefacts discovered on the Su-re website as being between 5,200 and 5,500 years outdated. These instruments had been seemingly associated to quarrying actions on the website.
Whereas some older websites have been found in central and southeastern Tibet, our dataset has made Su-re the oldest securely dated website within the central-southern Tibetan Plateau close to the excessive Himalaya.
This discovering is especially thrilling contemplating the proximity of Su-re to the “Nangpa La” mountain cross. This cross has traditionally related native Tibetans within the highlands with Nepali Sherpas within the Himalayan valleys and lowlands.
Our new strategy to analysing floor artefacts will be thought of the start of a street to new archaeological views. Sooner or later it may assist uncover the secrets and techniques of lithic artefact websites world wide. — PTI