Final answer:
The Nile's soil, called Kemet, is between 10 and 20 miles wide and was formed from fertile all uvial sediments deposited by annual flooding, which created agriculturally rich land that could support abundant harvests.
Step-by-step explanation:
The soil of the Nile, known as Kemet by the ancient Egyptians due to its rich black color, is between 10 and 20 miles wide. This fertile land was created by the annual flooding of the Nile, which deposited nutrient-rich all uvial sediment along its banks. The Nile Valley's agricultural fertility is a result of this sediment, which washed down from the Ethiopian highlands with the floodwater, providing the necessary nutrients for a highly productive agricultural system that could sustain harvests three times as bountiful as those in regions like Mesopotamia. Despite its productivity, the introduction of the Aswan High Dam in 1968 changed the landscape of Nile's agriculture by controlling the flooding, which has led to both benefits and challenges such as a buildup of salt in the soil, thereby affecting its long-term fertility.