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Today's reading comprehension:
Today, the Black Sea is a brackish inland sea, fed by fresh water from European rivers and saltier, Mediterranean seawater flowing in through the Bosporus strait. In the 1970s and 1980s, cores through now submerged sediments off the northern and western coasts revealed the remains of a coastal plain that was exposed late in the last ice age and into the interglacial warmth of the past 10,000 years. Long after glacial melt waters began raising world sea levels, it seems, the Black Sea was a freshwater lake, much smaller and lower than today's sea; it was cut off from the Mediterranean because the level of that sea was even lower than the Bosporus.
Evidence that a rising Mediterranean suddenly refilled this lowered Black Sea emerged from a joint Russian US expedition in 1993, during which researchers used seismic waves to image the layers of sediment at the bottom of the Black Sea. If rising waters had crept slowly across the coastal plain, they would have deposited a wedge of sediment as they went. But as Ryan, Pitman, and colleagues reported in Marine Geology last year, they saw no sign of that. Instead they found a thin, uniform dusting of sediment, consistent with a geologically instantaneous refilling of the Black Sea.
In addition, radiocarbon dating of the shells of the first salt tolerant molluscan invaders from the Mediterranean yielded the same age—7550 years before present, plus or minus 100 years—regardless of whether the shells came from deep, permanently flooded sediments or from the shallow shelf. If the refilling had been gradual, the team reasoned, the shells in deeper water would have been laid down first.
Finally, seismic probing has shown that the hard rock basement beneath the sediments filling the Bosporus channel lies at a depth of nearly 100 meters, rather than 35 meters, as had been thought. So the floodwaters could have cut a very deep channel through the sediments and down to bedrock, letting the water spill through far faster.
1. The purpose of the author in writing the text is to
A outline the geographical features of the Bosporus.
B explain why the Black Sea was a freshwater lake.
C describe a joint RussianUS expedition to the Black Sea.
D provide new evidence that a rising Mediterranean suddenly refilled the lowered Black Sea.
2. By referring to the report of the expedition team, the author shows that
A the Black Sea was gradually refilled 10,000 years ago.
B a wedge of sediment was found at the bottom of the Black Sea.
C the hard rock basement beneath the sediments filling the Bosporus channel lies at a depth of nearly 35 meters.
D a thin and uniform dusting of sediment with a geologically instantaneous refilling of the Black was found.
3. “Brackish” water (Line 1, Para.1) is not pure because it is
A slightly salty.
B unclear.
C polluted.
D not fresh.
4. The text is most likely a part of a
A journalist interview.
B book review.
C scientific report.
D narrative story.
5. If a rising Mediterranean had gradually refilled the lowered Black Sea,
A the floodwaters would have left a thicker, uniform dusting of sediment.
B the Black Sea would have become a much smaller freshwater lake.
C radiocarbon dating of the shells from deeper sediments would have yielded older age than those from shallow shelf.
D the hard rock basement beneath the sediments filling the Bosporus would have lain at a depth of 35 meters.
Vocabulary:
(in order to improve your ability of guessing words, you'd better see this section after you answer the quenstions)
1.brackish [ 'brækiʃ ] a.(指水)略咸的 ［同义］ saltish, somewhat salt
2.flow in through 不断涌入
3.coastal plain 沿海平原
4.refill v.再装满，再充满
5.seismic [ 'saizmik ] a. 地震的 ［例］ seismic research 地震研究
6.sediment [ 'sedimənt ] n.沉淀物 ［同义］ dregs, lees, settlings, grounds
7.radiocarbon [ 'reidiəu'kɑ:bən ] n.放射性炭
8.molluscan [ mɔ'lʌskən ] n.软体动物
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本帖最后由 Alice-nemo 于 2008-7-9 11:03 编辑 ]
