Egypt Felled by Famine
Even ancient Egypts mighty pyramid builders were powerless in the face of the famine that helped bring down their civilian around 2180 BC.Now evidence gleaned from mud deposited by the River Nile suggests that a shift in climate thousands of kilometers to the south was ultimately to blem 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 amounts 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 analyzing 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 river.
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 4,500 to 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 Institution in Washington,D.C:" Anything humans do to shift the climate belts would have an even worse effect along the Nile system because the populations have increased dramatically
Why does the author mention "pyramid builders"?
A. Because they once worked miracles.
Because they were well-built.
C. Because they were actually very weak.
D. Because even they were unable to rescue their civilization.
Sunbath and Skin Cancer
In the summer, millions of Americans will offer up their bodies to the sun rays. A tan indicates health and beauty, and most sun worshippers will sacrifice a lot to achieve it, including themselves.
With each hour, the sun's ultraviolet (紫外线的) radiation produces irreversible (不可逆的) damage, hastening the development of unsightly wrinkles. And with each year on the beach or rooftop, the sunbather increases his risk of getting skin cancer. Skin cancer is by far the most common form. of cancer. An estimated 400,000 new cases will be detected this year in the United States, and almost all of them can be blamed on over-exposure to the sun.
Fortunately ,most of these cancers are highly curable. But they can be disfiguring and take time to treat. For that reason, sun worshippers should treat deity with a good deal of awe(敬畏). Sunburn, of course, is the initial hazard posed by UV radiation. Prolonged exposure to UV, however, interferes with the production of collagen fibers in the dermis (真皮层), causing the skin to lose elasticity (弹性) and creating premature wrinkles. Further deterioration (恶化) of the dermis deprives the epidermis (表皮层)of nutrition and causes it to become thin and dry.
Cancer is UV's final result. Shortwave radiant energy, especially from the UV-B band, breaks the strands of DNA.Enzymes (酶) work constantly to rearrange the (变异的) DNA into proper sequence, but with repeated UV exposure, the repair process may eventually break down. Then the mutant DNA may produce a colony of cancer cells. But skin cancer may be avoided with a good dose of common sense. People with fair skin and blue eyes who burn easily stand the highest risk. Special danger spots are the parts of the body most constantly exposed to the sun, such as the cheeks, nose, lower lip and the ears. People who have already developed precancerous (癌变前的) lesions (伤害) or had one skin-cancer growth stand a greatly increased chance of developing others.
Dermatologists (皮肤科医生) recommend avoiding the sun when it is most intense between 11 a.m. and 3 p. m. Anyone who insists on sunbathing should use a good sun screen. These lotions and salves contain chemicals that block out the burning UV-B radiation while permitting the tanning rays to reach the skin.
Which of the following is the result, if a sunbather stays on the beach for a long time?
A. The skin cancer.
B. The wrinkles that cannot be seen.
C. All kinds of sacrifices.
D. Healthful beauty.