Scientists have found the first direct evidence that could explain the sudden fall of the Old Kingdom of Egypt, one of the best organised civilisations the world has ever seen.
The Egyptians relied on the Nile flooding its banks annually at the height of summer. This would spread water and fertilising sediment across the dry Egyptian fields enabling crops to grow. The Egyptians had no idea what caused the floods, imbuing them with religious significance.
Hieroglyphic texts point to a 30-year period when the Nile failed to flood, around 2160BC. Until now, this explanation has been supported only by historical and archaeological evidence. But a team led by Michael Krom, an environmental geochemist at Leeds University, has found geological evidence that he believes supports the theory.
Professor Krom's team examined sediment samples from the Nile, collected by Jean-Daniel Stanley at the Smithsonian Institution in Washington. The Nile, the longest river in the world, begins as the White Nile in east central Africa. In the Ethiopian highlands, it joins the Blue Nile and flows on to Egypt and the Mediterranean.
Professor Krom and his team measured the ratio of isotopes of strontium in the samples. They found sediment from the White Nile is higher in Sr87 compared with that from the Blue Nile, which contains relatively more Sr86.
When they investigated samples from the Nile delta, they saw a decrease in the ratio of Sr87 to Sr86 over the period from 4500BC to 2200BC, caused by a decreasing flood transporting relatively more sediment from the Blue Nile.
The team also discovered distinctive reddish-brown silt layers in the samples, characteristic of sediment allowed to dry out in air. These were deposited around 2250BC to 2050BC, implying that the Nile had dried out.
Professor Krom presented his findings to the Environmental Catastrophes and Recoveries in the Holocene conference at Brunel University last week.
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