Sometimes archaeological evidence may be quite clear, but the story it tells can be mystifying. One such conundrum has been archaeological evidence of relatively intense hilltop farming thousands of years ago in the relatively arid Jerusalem area, the Judean lowlands and northern West Bank. The Iron Age and Byzantine farmers cultivated the chalky, hilly land mostly by terracing. Meanwhile in the abundantly rainy Galilee in Israel’s north, there is no evidence of terracing. The area was just as densely populated but the people seem to have eschewed exploiting the hills, only cultivating crops at low level. It seemed counterintuitive to find the evidence of heavier farming in the drier lands of Jerusalem and Samaria than in the lovely Galilee.
Now a new study by geologists may have explained why. It boils down to proximity to the Negev and the loess soil on its surface, which blew as far as Jerusalem and Samaria but not further north, suggest Dr. Rivka Amit and Dr. Onn Crouvi of the Geological Survey and Prof. Yehouda Enzel of Hebrew University’s Hermann Institute of Earth Sciences in the journal Geology.
The geological team hadn’t set out to resolve this archaeological riddle. They had been wondering what the Negev was like before the loess surface developed, and to resolve the geological conundrum of where the loess had originated.
Loess is basically sediment, a mix of sand, clay and silt, loosely cemented by minerals. This mix, which is coarser than just sand, coats the surface of most of the northern and central Negev. Elsewhere in the world, loess is usually formed by the advance and retreat of glaciers: These juggernaut rivers of ice erode rocks into sand and silt. This cannot apply to the loess in the Negev, however, if only because its loess is relatively young, a mere 200,000 years old and Israel was not glaciated at that time. Nor could the loess have been blown in from the Sahara or Arabia because the wind can’t carry particles so big that far.
Dust in the wind
To resolve the question of the source of the loess, the geologists analysed dust on hilltops throughout Israel. The heights are the only place where dust settles from the atmosphere before mixing with other substances or being affected by contact with streams, for example.
“Dust storms from distant places such as the Sahara can carry in fine grains that are less than 10 microns in size,” says Amit. But the loess grains are 20 to 60 microns in size. Moreover, analysis shows the loess particles are mostly quartzy, not chalky. It bears adding that most of the surface rock in Israel is chalky, certainly in central Israel, because in distant prehistory, this area was under the sea.
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Ergo the loess had to have come from a source closer than the Sahara and completely unrelated to glaciation, and the only source in reasonable proximity is erosion of sand dunes in the Negev itself and the Sinai, under more violent climatic conditions than we’re used to. Strong winds in the region during the Upper Pleistocene caused the grains to collide and disintigrate into the silt from which loess is born.
As it formed, the loess also moved. The wind blew the particles dozens of kilometers away, where they settled, as far away as central Israel and Samaria but the wind wasn’t strong enough to blow the loess particles further north.
And thus Israel’s southern regions have thicker loess than the north, which is where farming comes in. The loess is hardly loam, but it’s better for cultivation than the soil resulting from erosion of chalky rock, which doesn’t hold water well.
To find support for their theory, the researchers looked at the island of Crete, which has no source of sand; anything soil on the mountaintops was dust transported by the wind, Amit explained. And what they found is that the soil in mountainous areas of Crete was similar to the hilltops in the Galilee.
So they did resolve their original riddle which is what the Negev looked like before the loess: similar to the arid landscape that characterizes Mediterranean islands.
Thus, soil in Israel has two sources. One source is dust carried thousands of kilometers from the Sahara or Arabia: tiny particles that are capable of creating no more than thin soil. The second is coarser particles of loess that can only be travel dozens of kilometers.
Central and southern Israel got both. The coarser loess particles created relatively dense, aerated soil that retains water better. The farther north one goes, and the farther from the Negev, the smaller the particles and the thinner the soil gets, particularly in the hills.
The researchers also cautiously postulate that it’s possible that proximity to deserts is part of the more general explanation for the Fertile Crescent in the Middle East, where agriculture and animal husbandry are believed to have begun some 12,000 years ago.
It bears noting that loess is not a boon for farmers. It is not rich in nutrients and needs augmentation. To cultivate the Negev, which they did for hundreds of years, the Byzantines built giant dovecotes in their fields, thus killing two birds with one stone: the bird poo fertilized the crops, enabling them to not only subsist but to export wine and olive oil; and the birds could also be eaten and sacrificed to the gods.
One way or another, it appears that these geological conditions are what encouraged agriculture to thrive on the hills of ancient Judea and Samaria, as is well-established by archaeology, while the Galileans had lovely rain but had to settle for growing food in the soil in the valleys. As Amit puts it: “Without the desert loess, it’s reasonable to assume that we wouldn’t have been the land of milk and honey.”