Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

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Domesticated livestock not only added their labor to increase harvests,
their manure helped replenish soil nutrients taken up by crops. The additional
crops then fed more animals that produced more manure and led in
turn to greater harvests that fed more people. Employing ox power, a single
farmer could grow far more food than needed to feed a family. Invention
of the plow revolutionized human civilization and transformed
Earth’s surface.
There were about four million people on Earth when Europe’s glaciers
melted. During the next five thousand years, the world’s population grew
by another million. Once agricultural societies developed, humanity began
to double every thousand years, reaching perhaps as many as two hundred
million by the time of Christ. Two thousand years later, millions of square
miles of cultivated land support almost six and a half billion people—5 to
10 percent of all the people who ever lived, over a thousand times more
folks than were around at the end of the last glaciation.
The new lifestyle of cultivating wheat and barley and keeping domesticated
sheep spread to central Asia and the valley of the Nile River. The
same system spread to Europe. Archaeological records show that between
6300 and 4800 bc adoption of agriculture spread steadily west through
Turkey, into Greece, and up the Balkans at an average pace of about half a
mile per year. Other than cattle, plants and animals that form the basis for
European agriculture came from the Middle East.
The first farmers relied on rainfall to water their crops on upland fields.
They were so successful that by about 5000 bc the human population
occupied virtually the entire area of the Middle East suitable for dryland
farming. The pressure to produce more food intensified because population
growth kept pace with increasing food production. This, in turn,
increased pressure to extract more food from the land. Not long after the
first communities settled into an agricultural lifestyle, the impact of topsoil
erosion and degraded soil fertility—caused by intensive agriculture
and goat grazing—began to undermine crop yields. As a direct result,
around 6000 bc whole villages in central Jordan were abandoned.
When upland erosion and the growing population in the Zagros Mountains
pushed agricultural communities into lowlands with inadequate rainfall
to grow crops, the urgent need to cultivate these increasingly marginal
areas led to a major revolution in agricultural methods: irrigation. Once
farmers moved into the northern portion of the floodplain between the
Tigris and Euphrates rivers and began irrigating their crops, they reaped
bigger harvests. Digging and maintaining canals to water their fields, set-
rivers of life