EGYPT: THE GIFT OF GEOLOGY

The emergence of Egypt as one of the most prominent civilizations in the history of humanity was made possible by a series of geologic and climatic events that shaped the Nile Valley, provided year round supply of water, and resulted in population clustered in the Nile Valley. Circa 20 Ma, rift-flank uplift of the Afar Depression and the Main Ethiopian Rift on the one hand and the Eastern and Western Branches of the East African Rift on the other hand reorganized the drainage system in Sub-Saharan Africa, directing water toward the lowlands of Sudan. Desiccation of the Mediterranean ~6 Ma resulted in carving of the Eonile Canyon from the northern border of Nubia to the Mediterranean, providing the geomorphic setting for what would become the Nile Valley. To the south, the Nuba Mountains and the Darfur Dome, produced by mantle plume-related uplift, were initial topographic barriers that directed the White Nile to the north. The Eonile became connected to waters of the Ethiopian Highlands through the ancestral Blue Nile only about ~1 Ma, bringing water and fertile sediments from the volcanic Ethiopian Plateau. Subsequent increase in uplift of the Ethiopian Plateau further increased the rate of sediment supply. To the southwest, the ancestral White Nile received water from Lakes Victoria and Albert, forming the 500-km-long White Nile Paleolake by about 400 Ka. Overflow from this lake connected the White Nile to the Blue Nile, forming the modern Nile. Connection of the Nile to waters in the Ethiopian Plateau and the East African Highlands is crucial to the existence of the Nile as the only trans-Saharan river, and connection to Ethiopian Plateau sediment sources is crucial to fertility of the floodplain. As rainfall decreased toward the end of the Early Holocene, climate change drove humans out of the Sahara toward the south and toward the Nile Valley. At the same time, post-Pleistocene deceleration in the rate of sea level rise promoted accumulation of cultivatable floodplain sediments along the Egyptian Nile. Both set the stage for the rise of Egyptian civilization. Building an introductory geology course around these events provides an outstanding opportunity for students to draw connections between geologic processes - tectonics, climate change, river evolution – and human events.