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Imported fertility.

Deserts and the oldest human cultures developed side by side. Human beings originated in the tropical savannahs of eastern Africa, where humanity's Pleistocene ancestors cultivated an unusual lifestyle and separated from the other higher primates. Over their evolution, humans occupied the world's biomes one after another, including the desert biome. The large rivers that cross the valleys and supply fertility from outside allowed the ancient civilizations to grow. They were the great river cultures that arose in the middle of the desert.

The first known great civilizations arose between the Tigris and the Euphrates. First came the Sumerians, then the Babylonians and the Assyrians. The conquerors who came from the west, the Macedonians of Alexander the Great (356-323 b.c.), gave the area the name Mesopotamia, meaning between the rivers. The annual surges of the Tigris and the Euphrates, the result of snow melting in their headwaters, caused flooding that fertilized the soil with a layer of silt and allowed cultivation. Because local rainfall was scarce and unpredictable, the former inhabitants of Mesopotamia were forced to dig irrigation channels and reservoirs, but did not have to fertilize their fields because this was done by the floods. But they did have to deal with other problems.

Excessively large freshets washed away their houses and livestock, and sandstorms covered the crops with the fine desert dust. The slightly saline river water deposited salts on the soil that the low rainfall did not wash away. As soil salinity increased, some crops could not be cultivated--first wheat, then barley, and lastly even date palms. The Sumerians soon realized the dangers of salinization and in the ancient equivalent of the Farmer's Almanac (from about 4,000 years ago), several techniques to avoid, or at least delay, salinization are described.

Despite these problems, the Sumerians and Babylonians were able to conquer the desert and turn it into productive ground. The legendary Hanging Gardens of Babylon built by the Queen Sammuramat (better known by her Greek name, Semiramis) are one of the seven wonders of the ancient world. They were sited on the palace of Nebuchadnez-zar (Nebuchadnezzar II, reigned 605-562 b.c.), and the engineers had to construct a complicated pumping system to raise water from the Euphrates in order to irrigate.

Another major river culture, that of ancient Egypt, had to resolve some problems similar to those of Sumeria and Babylon. The Egyptians were even more dependent on the Nile than the Babylonians were on the Tigris and Euphrates. As there are hardly any rains in Egypt, the entire country's survival depended on the flooding of the Nile. For this reason, the Egyptians have, since antiquity, used a calendar to foresee the flooding of the river; along the banks, they made graduated markers to measure the changes in the water level and thus predict the harvests. Egyptian engineers constructed an excellent system of dikes, reservoirs, and canals to control dangerous surges and irrigate crops. About 3,600 years ago, they invented the shaduff, a simple but effective irrigation device consisting of a bucket tied to a stick as a counterweight; it is still used to raise water.

The Nile allowed the Egyptians to cultivate a wide range of crops (barley, wheat, melons, dates, figs, leeks, onions, garlic, cucumbers, radishes, beans, and lettuce) and raise livestock (cows, sheep, goats, and pigs), and also provided fish for consumption, salt and soda to preserve foodstuffs, and mud that could be mixed with straw and used for building. The only thing it did not provide was good quality wood; the local trees, mainly acacias and sycamores, were knotty and poor in resins.

The third great river culture of the deserts developed in the Indus Valley in contemporary Pakistan. The Indus has its source in the Kailasrange (Kangrinboje Feng) north of the Himalayas, crosses the fertile plains of the Punjab and the Sind, and flows into the Arabian Sea. About 5,000 years ago, some of the inhabitants of the Iran Plateau went down to the Indus Valley, where they founded settlements like Kechi Beg, Armi, Nal, Nuandara, Zhob, and Loralai. The culture was at its peak around 2500-1800 b.c., with thriving cities like Mohenjo-Daro and Harappa. The influence of these two cities spread from the Gulf of Oman to the banks of the Amu-Darya River in northern Afghanistan.

Like the Babylonians and Egyptians, the ancient inhabitants of the Indus Valley depended on the annual flooding of the river. They also built large irrigation and flood control installations to deal with the flooding that occurred in March, when the snow and ice in the Himalayas melted. Their main crops were wheat and barley, but they also cultivated rice, mustard, sesame, dates, melons, and cotton. They raised buffaloes, sheep, and pigs and used elephants, horses, and camels as beasts of burden. The cities had immense granaries to store cereals and platforms with mortars to grind the grain. The granaries acted as treasuries since, as in Mesopotamia, wheat and barley were used as money.

All this is ancient history, but there still remains the paradox that the great cultures of antiquity arose in the heart of the inhospitable desert spaces. The inhabitants, however, knew how to make use of imported fertility.
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Publication:Encyclopedia of the Biosphere
Date:Apr 1, 2000
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