tibetan barley harvest
November 22, 2014

Human Settlements And Hidden Canyons On The Roof Of The World

Brett Smith for redOrbit.com - Your Universe Online

Human settlements have popped up in some of the most remote locations on Earth, and a new study in the journal Science has revealed that about 3,600 years ago, an agricultural society subsisted on the Tibetan Plateau, the so-called 'roof of the world'.

The new report is based on archaeological evidence across 53 sites, spanning 800 miles. An analysis of the evidence gathered from these sites painted a picture of an agrarian society thriving 8,200 feet to 11,200 feet above sea level.

Previously found archaeological evidence has found that humans have been roaming the Tibetan Plateau for the last 5,000 years. However, proof of a sustained settlement had never been established until now.

"Until now, when and how humans started to live and farm at such extraordinary heights has remained an open question,” said study author Martin Jones, an archaeologist from the University of Cambridge. “Our understanding of sustained habitation above (6,500 to 9,800 feet) on the Tibetan Plateau has to date been hampered by the scarcity of archaeological data available.”

"But our findings show that not only did these farmer-herders conquer unheard of heights in terms of raising livestock and growing crops like barley and millet, but that human expansion into the higher, colder altitudes took place as the continental temperatures were becoming colder,” Jones added.

To determine what period of time and at what altitude included a long-lasting human presence, the study group amassed artifacts, animal bones and plant remains from 53 locations across the Tibetan Plateau. Cereal grains were discovered at all 53 locations and animal bones were uncovered at ten locations. Of the 53 locations, a group dating from 5,200 to 3,600 years ago reached a maximum elevation of close to 8,300 feet while a later group found in 29 locations – dating from 3,600 to 2,300 years ago – neared 11,200 feet in altitude, the researchers found.

Image Above: This photo shows the Yarlung Tsangpo Valley close to the Tsangpo Gorge, where it is rather narrow and underlain by only about 250 meters of sediments. The mountains in the upper left corner belong to the Namche Barwa massif. Previously, scientists had suspected that the debris deposited by a glacier in the foreground was responsible for the formation of the steep Tsangpo Gorge -- the new discoveries falsify this hypothesis. Credit: Ping Wang

From ancient archaeology to an ancient geology

Another recently published study which focused in the Tibetan lowlands revealed evidence of an ancient canyon that slowly filled in over thousands of years.

The study, also published in Science, provides a strong case against a prevailing model for how the Himalayas became so steep.

"When I first saw the data, I said, 'Wow!' It was amazing to see that the river once cut quite deeply into the Tibetan Plateau because it does not today,” said study author Jean-Philippe Avouac, a professor of Geology at Caltech. “That was a big discovery, in my opinion."

Geologists have theorized that when rivers began to cut into a plateau, they gouged out the sides, slowly carving the plateau over time. However, the rivers presently streaming throughout the Himalayas have not cut much into the Tibetan Plateau. For that reason, the theory has become that a fast uplift in the Himalayas has pinned the rivers back, preventing them from making much progress. However, that theory fails to work with the newly found "paleocanyon" – which was created by a river carving deeply into the Tibetan Plateau.

The new find effectively rules out a 15-year-old theory called ‘tectonic aneurysm’, which suggests that the rapid uplift seen at steep knickpoints in Himalayan rivers were caused by intense river incision. In the tectonic aneurysm model, a river cuts down so fast – it causes the crust to heat up, weakening a nearby mountain range and empowering uplift.

"But now we have discovered that the river was able to cut into the plateau way before the uplift happened," Avouac says, "and this shows that the tectonic aneurysm model was actually not at work here. The rapid uplift is not a response to river incision."

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