The Geologic History of the Mediterranean

In 1970 geologists Kenneth J. Hsu and William B. F. Ryan were collecting research data while aboard the oceanographic research vessel Glomar Challenger. An objective of this particular cruise was to investigate the floor of the Mediterranean and to resolve questions about its geologic history. One question was related to evidence that the invertebrate fauna (animals without spines) of the Mediterranean had changed abruptly about 6 million years ago. Most of the older organisms were nearly wiped out, although a few hardy species survived. A few managed to migrate into the Atlantic. Somewhat later, the migrants returned, bringing new species with them. Why did the near extinction and migrations occur?

Another task for the Glomar Challenger’s scientists was to try to determine the origin of the domelike masses buried deep beneath the Mediterranean seafloor. These structures had been detected years earlier by echo-sounding instruments, but they had never been penetrated in the course of drilling. Were they salt domes such as are common along the United States Gulf Coast, and if so, why should there have been so much solid crystalline salt beneath the floor of the Mediterranean?

With questions such as these clearly before them, the scientists aboard the Glomar Challenger proceeded to the Mediterranean to search for the answers. On August 23, 1970, they recovered a sample. The sample consisted of pebbles of hardened sediment that had once been soft, deep-sea mud, as well as granules of gypsum [1] and fragments of volcanic rock. Not a single pebble was found /(后面的从句是修饰 pebble 的)that might have indicated that the pebbles came from the nearby continent. In the days following, samples of solid gypsum were repeatedly brought on deck as drilling operations penetrated the seafloor. Furthermore, the gypsum was found to possess peculiarities of composition and structure that suggested it had formed on desert flats. Sediment above and below the gypsum layer contained tiny marine fossils, indicating open-ocean conditions. As they drilled into the central and deepest part of the Mediterranean basin, the scientists took solid, shiny, crystalline salt from the core barrel. Interbedded with the salt were thin layers of what appeared to be windblown silt.

The time had come to formulate a hypothesis. The investigators theorized that about 20 million years ago, the Mediterranean was a broad seaway linked to the Atlantic by two narrow straits. Crustal movements closed the straits, and the landlocked Mediterranean began to evaporate. Increasing salinity caused by the evaporation resulted in the extermination of scores of invertebrate species. Only a few organisms especially tolerant of very salty conditions remained. As evaporation continued, the remaining brine (salt water) became so dense that the calcium sulfate of the hard layer was precipitated. In the central deeper part of the basin, the last of the brine evaporated to precipitate more soluble sodium chloride (salt). Later, under the weight of overlying sediments, this salt flowed plastically upward to form salt domes. Before this happened, however, the Mediterranean was a vast desert 3,000 meters deep. Then, about 5.5 million years ago came the deluge. As a result of crustal adjustments and faulting, the Strait of Gibraltar, where the Mediterranean now connects to the Atlantic, opened, and water cascaded spectacularly back into the Mediterranean. Turbulent waters tore into the hardened salt flats, broke them up, and ground them into the pebbles observed in the first sample taken by the Challenger. As the basin was refilled, normal marine organisms returned. Soon layers of oceanic ooze began to accumulate above the old hard layer.

The salt and gypsum, the faunal changes, and the unusual gravel provided abundant evidence that the Mediterranean was once a desert.

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gypsum: a mineral made of calcium sulfate and water

words:

objective 目标

cruise 航行

domelike 圆顶形状的

mass 块

penetrate 穿透

pebble 鹅卵石

granule 颗粒

peculiarity 特点 peculiar 奇特的

interbedded 混层的

windblown 风吹的

silt 淤泥

strait 海峡

salinity 含盐量

extermination 灭绝 extinction

precipitate 沉淀,促成

fault (地理)断层

deluge 洪水

cascade 瀑布,奔流

spectacular 壮观的 spectacle

speculate 推测

turbulent 动荡的

ooze 稀泥

gravel 沙砾

scores of 大量的 score(正式)大量

文章结构分析

题目解析

What does the author imply by saying “Not a single pebble was found that might have indicated that the pebbles came from the nearby continent”?

  • A.

    The most obvious explanation for the origin of the pebbles was not supported by the evidence.

  • B.

    The geologists did not find as many pebbles as they expected.

  • C.

    The geologists were looking for a particular kind of pebble.

  • D.

    The different pebbles could not have come from only one source.

A,第一个 that 引导的从句修饰 pebble,意思是没有证据表明这些pebble来自于附近的大陆。但是如果改成这样:Not a single pebble was found, which might have indicated that the pebbles came from the nearby continent. 意思就完全相反,这句话表达了 pebble 来自于附近的大陆,证据是没找到单块的石头。

Which of the following can be inferred from paragraph 3 about the solid gypsum layer?

  • A.

    It did not contain any marine fossils.

  • B.

    It had formed in open-ocean conditions.

  • C.

    It had once been soft, deep-sea mud.

  • D.

    It contained sediment from nearby deserts.

A,由于上一道题理解错误导致的

The word “scores” in the passage is closest in meaning to

  • A.

    members

  • B.

    large numbers

  • C.

    populations

  • D.

    different types

B

Which of the following can be inferred from paragraph 4 about the salt domes in the Mediterranean?

  • A.

    They began as layers of oceanic ooze. (oceanic ooze 是在 dome 形成之后附着上去的,最后一句)

  • B.

    They contain large quantities of calcium sulfate.(在沙漠中上一层的,是硫酸钙,deeper 的是氯化钠)

  • C.

    They were destroyed when the basin refilled with water. (在灌水之后形成的)

  • D.

    They formed after the Mediterranean basin refilled with water.

D

Q.E.D.


To baldly -_- go no man has gone before