Black Genesis: The Prehistoric Origins of Ancient Egypt

The surface of the now-covered bedrock was scoured by constant winds during many thousands of years of dry
periods leading up to 9000 BCE. An area of softer bedrock was scoured more deeply by the winds, which created the
depression that filled with water every summer season to become the playa during the monsoon season. This lasted to
around 3500 BCE, after which the region became the hot, hyperdry place that it is today. The last humid period in the
Egyptian Sahara, which lasted from about 9000 BCE to 3500 BCE, seems also to have ended abruptly. Yet scientists
also know that there have been several humid periods before this last one. Paleoclimatologists are finding that humid or
wet periods in the Sahara occur with curious regularity, which suggests that these periods might be linked to Earth’s
cyclical geological changes. Paleoceanographer and marine geologist Peter B. deMenocal studied sediment cores from
the eastern Atlantic Ocean to measure the past climate of the Sahara. These sediments, which were originally created by
wind-carried dust and sand that then settled to the bottom of the ocean to form layers, act as graduations for measuring
climate changes over long periods of time in the same way that rings in tree trunks can tell us of annual weather
variations. The phases of the humid periods that deMenocal found in the ocean sediments matched those that the
geologists found in the sediment layers at Nabta Playa. DeMenocal was able to show that the humid Sahara periods
occurred regularly, about every twenty thousand years, and, furthermore, that they always began and ended suddenly.
According to deMenocal, the cause of these sudden climate fluctuations from humid to dry were linked to the cyclical
changes of Earth’s motion with respect to the fixed stars. 5
The basis of deMenocal’s research relating climatic changes to the fixed stars began in 1920. Interestingly, in that
same year Ahmed Hassanein and Rosita Forbes undertook their fateful expedition to the Kufra oasis (which eventually
led to the discovery, a few years later, of the massifs of Jebel Uwainat and Gilf Kebir), and in that year the Serbian
mathematician Milutin Milankovitch (1879–1958) published his controversial paper that would become a foundation in
the science of climate change. 6 The Milankovitch Curve, as his theory is known, was based on an elegant and simple
notion: the small, gradual, annual changes in Earth’s orbit around the sun as well as the spin of its axis when considered
over many thousands of years will create sizeable recurring cycles causing Earth to receive sometimes more, sometimes
less light and heat from the sun, which will cause significant climate changes. These changes are the result of three
phenomena of Earth’s movements: precession, obliquity, and eccentricity.
1. Precession is a gyrating motion of Earth’s axis, which causes the planet to wobble like a spinning top, making a
complete cycle every twenty-six thousand years or so.
2. Obliquity is the angle of tilt that Earth’s axis makes with the plane of its orbit around the sun. This angle moves up
and down in a slow cycle of about forty-one thousand years, known as the obliquity of the ecliptic. Today the angle
is 23.4 degrees, but, for example, in 5000 BCE it was about 24.1 degrees. Like the precession cycle, astrophysicists
today can calculate with a great deal of accuracy exact changes in past and future obliquity. 7
3. Eccentricity is the elongatedness (that is, the perihelion and aphelion) of Earth’s elliptical orbit around the sun,
which changes in a complex cycle of about one hundred thousand years. *4
Precession and the Zodiacal Belt
The sun at the equinoxes (March 21 and September 22) is located in the sky against a backdrop of a particular group of
stars or constellations that lie along the so-called zodiacal belt. Every year the position of the sun along the zodiacal belt
at the equinoxes moves, or precesses, a tiny amount so that, in about twenty-six thousand years, the sun makes a
complete cycle around the entire zodiac. Although the precise number of years per each full precession cycle always
changes a bit, astrophysicists today can calculate the duration of precessional cycles, past and future, with a great deal
of accuracy. 8
These three effects—precession, obliquity, and eccentricity—when taken together, cause long-term climate change
every twenty thousand to twenty-six thousand years—such as, for example, the great ice ages known to have occurred in