职称英语综合类阅读理解真题
Ancient Egypt Brought Down by Famine
Even ancient Egypts mighty pyramidbuilders were powerless in the face of the faminethat helped bring down their civilization around 2180 B.C..Now evidence collected from mud deposited by the River Nile suggests that a shift in climate thousands of kilometers to the south was ultimately to blame--and the same or worse could happen today.
The ancient Egyptians depended on the Niles annual floods to irrigate their crops.But any change in climate that pushed the African monsoonssouthwards out of Ethiopia would have reduced these floods.
Declining rains in the Ethiopian highlands would have meant fewer plants to stabilize the soil.W.1len rain did fall it would have washed large amounts of soil into the Blue Nile and into Egypt，along with sedimentfrom the White Nile.
Blue Nile mud has a different isotopesignature from that of the white Nile.So by analyzing isotope differences in mud deposited in the Nile Delta.Michael Krom of LeedsUniversity worked out what proportion of sediment came from each branch of the river.
Krom reasons that during periods of drought，the amount of Blue Nile mud in the river would be relatively high.He found that one of these periods，from 4500 to 4200 years ago。immediately came before the fall of the Egypts old Kingdom.
The weakened waters would have been disaster for the Egyptians.Changes that affect food supply dont have to be very large to have a rippleeffect in societies，says Bill Ryan of the Lamont Doherty Earth Observatory in New York.
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