Egypt Felled by Famine
Even ancient Egypt's mighty pyramid builders were powerless in the face of the famine that helped bring down their civilisation around 2180 BC. Now evidence gleaned from mud deposited by the River Nile suggests that a shift in climate thousands of kilometres to the south was ultimately to blame--and the same or worse could happen today.
The ancient Egyptians depended on the Nile's annual floods to irrigate their crops. But any change in climate that pushed the African monsoons southwards out of Ethiopia would have diminished these floods.
Dwindling rains in the Ethiopian highlands would have meant fewer plants to stablise the soil. When rain did fall it would have washed large mounts of soil into the Blue Nile and into Egypt, along with sediment from the White Nile.
The Blue Nile mud has a different isotope signature from that of the White Nile. So by analysing isotope differences in mud deposited in the Nile Delta, Michael Krom of Leeds University worked out what proportion of sediment came from each branch of the fiver.
Krom reasons that during periods of drought, the amount of the Blue Nile mud in the river would be relatively high. He found that one of these periods, from 4,50Oto 4,200 years ago, immediately predates the fall of the Egypt's Old Kingdom.
The weakened waters would have been catastrophic for the Egyptians. "Changes that affect food supply don't have to be very large to have a ripple effect in societies," says Bill Ryan of the Lamont Doherty Earth Observatory in New York.
"Similar events today could be even more devastating," says team member Daniel Stanley, a geoarchaeologist from the Smithsonian Institutions in Washington, D. C.. "Anything humans do to shift the climate belts would have an even worse effect along the Nile system today because the populations have increased dramatically."
Why does the author mention "pyramid builders"?
A.Because they once worked miracles.
B.Because they were well-built.
C.Because they were actually very weak.
D.Because even they were unable to rescue their civilisation.
第1题
A.使进气速度场分布不均匀和使气流发生局部分离,引起压气机叶片的振动
B.冰屑脱离,进人压气机,而造成压气机的机械损伤
C.结冰堵塞进气道,使得进入压气机的气流明显减少,导致发动机富油停车
第2题
进气管道结冰将导致危险后果,下列描述不正确的是()
A.冰屑脱离,进入压气机,造成压气机机械损伤
B.使进气速度场分布不均匀,发生局部分离,引起压气机叶片振动
C.结冰堵塞进气道,使得进入压气机的气流明显减少,导致发动机富油停车
第6题
A.地球自转和海陆分布
B. 太阳辐射随纬度分布不均匀和海陆分布
C. 太阳辐射随纬度不均匀和地球自转(地转偏向力)
D. 太阳辐射随纬度分布不均匀和地形影响
为了保护您的账号安全,请在“上学吧”公众号进行验证,点击“官网服务”-“账号验证”后输入验证码“”完成验证,验证成功后方可继续查看答案!