Saharan Exodus

By 5,500 years ago humans had abandoned the Sahara-- not by choice, not due to over hunting, or anything they had done: they were driven out by climate change produced by small perturbations in Earth’s orbital dynamics. The desertification of the Sahara was devastating to the hunter-gatherers who had been living there for thousands of years. For them, the end of the African Humid Period 5,500 years ago was of greater significance than the end of the last ice age 12,000 years ago. As the climate dried, people migrated toward the remaining lakes and rivers. To survive humans had to become ever more resourceful. They had to adapt or die. It forced them to find a new way of life, to invent new modes of survival. This led first to the domestication of cattle, followed by farming. As desertification continued, people concentrated in the Nile Valley, which became habitable as flows decreased. There they huddle together like animals at a watering hole. For them, the Nile Valley became a haven. After being driven from their homeland, the former hunter-gatherers had the fabulous good fortune of reaching the Nile Valley just as some of the best agricultural land in the world was exposed. Just over 5,000 years ago they reached the Cairo area. It was climate change that forced the migration to the Nile Valley, which then gave rise to the Egyptian civilization, animal domestication, and agriculture. They had no way of knowing they had laid the foundation of the most successful civilization the world has ever seen. By concentrating they brought diverse technology and ideas together. Rock art evolved to become writing. Knowledge could now be effectively passed between generations. The world had changed, humans were no longer at the mercy of the forces that surrounded them. Their art, architecture, and government has helped to shape our modern world. The Anthropocene had begun.

Giza Cuesta

The landscape we see today at Giza bears only a passing resemblance to what the ancient Egyptians found. Over 34 million years, through the combined action of precipitation, the Nile River, windblown sand, and even at times ocean waves, the bedrock had been worn down to an erosion resistant layer of limestone. The differential rates of erosion produced a hill that geologists call a cuesta. Cuestas are gentle sloping hills that follow bedding planes, with a steep slope or cliff on the opposite side. The cliff on the far side is called an escarpment. To an untrained eye, cuestas are often mistaken for plateaus, as with the Giza Plateau. The distinguishing feature of a cuesta is a cliff that exists only on one side, whereas plateaus have cliffs on all sides. The Giza Cuesta was selected to build pyramids on for several reasons. It contained a source of high- quality limestone that was used to construct the pyramids. At the time the Nile River flowed just east of the Sphinx. The land slopes to the south-east forming a natural ramp from the Nile River to the pyramids. Perhaps, most importantly from the top of the hill the pyramids would be visible for miles in all directions.

Sphinx Construction

Work on the Sphinx began 4,500 years ago as construction of the Khafre pyramid complex was underway. By the time work began on the Sphinx, most of the erosion resistant limestone had been quarried. It was from a portion of the remaining limestone the Sphinx head was carved. The causeway linking the Mortuary Temple and the Valley Temple was laid out, if not already built -- all part of a single master plan. With characteristic precision, the Sphinx and the Sphinx quarry walls were carefully aligned with the cardinal coordinates, except for the southern quarry wall which abuts up against the preexisting causeway. Sitting on solid bedrock, the causeway clearly predates the Sphinx quarry. From a purely geotechnical point of view, the ground-plan of the Giza monuments, including the pyramids and Sphinx, speaks clearly to construction 4,500 years ago. The ancient Egyptians were master stone workers, and the Sphinx itself was carefully designed. This was accomplished in part through a geotechnical investigation including test borings. Information gathered from the site investigation was used to design the Sphinx. The overall scale of the statue was set by the size of a fracture free block of erosion resistant limestone from which the head was carved. Facial features of the eyebrows, nose, and lips were adjusted to align with natural bedding planes. The height of the head was restricted by the thickness of the erosion resistant limestone. It appears likely that the face profile was set by a nearly vertical bedrock fracture. The head and rear paws were carved directly from the natural limestone bedrock. I believe it was through the geotechnical investigation the artist discovered the limestone of the body was too soft to carve. Rather than abandon the project, he decided to cover the central section of the Sphinx body with a veneer of high quality limestone blocks. For the most part, carving was accomplished by flaking the limestone off with two-handed stone pounders and stone hammers. Copper chisels were only used for detailed work. Based on my research, the soft limestone of the body was flaked off, producing the undulating surface we see today. The irregular surface was then fitted with a veneer of high-quality limestone blocks. These blocks were then carved to form the center section of the Sphinx body. The undulating surface was revealed after the high-quality block veneer was looted. Working from the top down, it was only after the head had been carved that a small cave within the body was discovered. Known as the Major Fissure, the cave is up to 2 m (6.5 ft) wide. It crosses the Sphinx from north to south forcing the artist to modify the design by elongating the body. This changed the proportions of the statue making the head appear too small when viewed from the side. Although no record of construction has yet been discovered, everything points to the Sphinx being part of the Khafre pyramid complex. Some of the limestone blocks used to construct the Khafre Valley Temple came from the Sphinx excavation, making the temple without question contemporaneous with the Sphinx. Taken together, the evidence indicates the Sphinx dates to 4,500 years ago.

Burning House Earth Anthropocene: 5,000-0 years ago