Dust may have governed ancient human civilization

The map shows the Levant region (shaded in orange), which is the western part of the entire fertile region (shaded in yellow); Study areas in Israel and Crete are in dashed boxes. Arrows from Sahara and Negev desserts show dust transport patterns, and their thicknesses reflect relative grain sizes. Fine-grained dust is transported from the Sahara to the Levant by air, and thick dust (loos) is transported a short distance from the Negev Desert to the Galilian Mountains in Israel. Credit: Rivka Amit et al. And geology

When early humans began to migrate out of Africa and spread to Eurasia over a hundred thousand years ago, a fertile region around the eastern Mediterranean Sea called the Levant served as an important gateway between North Africa and Eurasia. used to do. A new study published in Geology, Shows that the existence of that oasis depends almost entirely on something we never think of: dust.

Dr. Rivka Amit, in the Geological Survey of Israel, and her team initially posed a simple question: Why are some soils around the Mediterranean thin and some thick? Their investigation showed them that not only did the deposition of dust play an important role in creating thick soil in the Levant, but also because the source of the dust had not changed 200,000 years ago, the early humans may have had a very difficult time leaving Africa. , And parts of the fertile crescent should not have been too active to take root for civilization.

Thick soils form in areas with wet, humid climates, and thin soils form in dry environments with low climatic rates. But in the Mediterranean, where most of the bedrock is carbonate, the opposite is true: the waiter is thin, unproductive soil in the northern regions, and thick, productive soil in the more arid southeastern regions. Some scientists have attributed these patterns to differences in rates of erosion driven by human activity. But for Amit, who has been studying the area for years, a high erosion rate alone made no sense. She challenged existing hypotheses, arguing that another factor — dust input — plays a significant role when weathering rates are too slow to form soil from bedrake.

To assess the impact of dust on Mediterranean soil, Amit and his team needed to bring the dust back to its original source. They collected dust samples from the soil in the region as well as from nearby and far-flung dust sources and compared the grain size distribution of the samples. The team identified an important distinction between areas with thin and thick soils: Thin soils contained the finest grain sizes saline from distant deserts such as the Sahara, while thicker, more productive soils contained coarse dust, near K was called Sour from the Negev Desert, and its vast dune region. Thick soils in the eastern Mediterranean formed over 200,000 years ago when glaciers covered large tracts of land, milling fountain and creating fine sediments in abundance. “The whole planet was very dusty,” said Amit, which allowed large-scale dune fields to form in the Negev, creating new sources of dust and eventually thick soils in places like the Levant.

Amit then had the answer: areas with thin soils simply did not have sufficient amounts of grain to form thick, agriculturally productive soils, while the southeastern Mediterranean was. “Erosion is less important here,” he said. “What’s important is whether you get fat flow [dust] Degrees. [Without that], You get thin, unproductive soil. ”

Amit did not stop there. She now knows that the thickest soil had received a large flow of coarse dust, which led to the area being designated as a “land of milk and honey” for agricultural productivity. His next question was, was it always like this?

He was surprised by what he found. When looking under the loop in the soil profile, they found a lack of fine grained sediment. “What was [deposited] Before there was very thin soil, “she said. It was a big surprise … the landscape was completely different, so I’m not sure people would be” [have chosen] To live in this area because it was a harsh environment and [an] Almost bare landscape, without much soil. “Without the changing winds and formation of the Negev dune region, then, the fertile region that served as a passage for early humans was probably very difficult to pass through and survive.

In the modern Mediterranean, soils are not deposited any more. “The source of the dust is cut off,” Amit explained, as the glaciers retreated into the Holocene, “now we are only working the old lost.” Even if there were a dust source, it would take thousands of years to rebuild a soil there. These leave the soil in a fragile state, and the people living there must balance conservation and agricultural use. Employing responsible farming practices in the area, as ladders have been used for thousands of years, is critical to soil conservation if agriculture is to continue.

Four application restores soil carbon and productivity

more information:
Rivka Amit et cetera, altered Mediterranean soil productivity and early human culture affected in quaternary inflow of adjacent coarse-grained soil, Geology (2020). DOI: 10.1130 / G47708.1

Provided by the Geological Society of America

Quotes: Dust may have revived ancient human civilization (2020, 15 September) on 15 September 2010 from https://phys.org/news/2020-09-ancient-human-civilization.html.

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