Day 22

英文重现

Relative land-ice volume for a given period can be deduced from the ratio of two oxygen isotopes,16 and 18, found in ocean sediments… The higher the ratio of oxygen 18 to oxygen 16 in a sedimentary specimen, the more land ice there was when the sediment was laid down.

As an indicator of shifts in the Earth's climate, the isotope record has two advantages. First, it is a global record: there is remarkably little variation in isotope ratios in sedimentary specimens taken from different continental locations. Second, it is a more continuous record than that taken from rocks on land.

——GMAT OG 2015, Reading Comprehension, Passage 15

解析

1.第一个句子的主干为“volume can be deduced from the ratio of two oxygen isotopes”，“16 and 18”是前面名词“two oxygen isotopes”的同位语，而“found in ocean sediments”是过去分词作后置定语，修饰前面的“two oxygen isotopes”；倒数第二句中的“taken from different continental locations”也是过去分词作后置定语，修饰前面的名词“sedimentary specimens”。

2.“the +比较级，the +比较级”，表示“越……越……”，表示一方的程度随着另一方的变化而变化，其中的两个“the”都是副词，后面必须是形容词或副词的比较级。比较的部分可以是表语、状语，也可以是主语和宾语，这种结构通常是从句在前，主句在后。主句可根据需要调整，采用正常语序或倒装语序，而从句必须是正常语序，例如：

The noisier they were, the happier was their mother.

他们越吵，他们的妈妈越高兴。

此处是形容“land ice”的数量随着“oxygen 18”与“oxygen 16”的比例高低而变化。

3.第二段中的“as”在这里作介词，译为“作为”；当“as”作连词时，可以引导

从句。

4.最后一句中的“than”后面省略了be动词“is”。“than”比较的是两个不同的记录（来自“different continental locations”和来自“rocks on land”的两个记录），这里的“that”为代词，指代“record”。

词义辨析

参考翻译

一定时间内陆地上的冰的数量能够通过从海洋沉积物中发现的两种氧同位素——16和18的比例推断出来……沉积物样品中氧18/氧16的比例越高，沉积物沉淀时所处的时期就拥有越多的陆地冰。

作为地球气候变化的一个指标，同位素记录有两个优点。一、它是一个全球性的记录：从不同大陆上采集的沉积物样品，其同位素比例很少有变化。二、相对于陆地岩石的记录来说，它是一个更具连续性的记录。

实战演练

To establish such a chronology it is necessary to determine the relative amounts of land ice that existed at various times in the Earth's past. A recent discovery makes such a determination possible: relative land-ice volume for a given period can be deduced from the ratio of two oxygen isotopes, 16 and 18, found in ocean sediments. Almost all the oxygen in water is oxygen 16, but a few molecules out of every thousand incorporate the heavier isotope 18. When an ice age begins, the continental ice sheets grow, steadily reducing the amount of water evaporated from the ocean that will eventually return to it. Because heavier isotopes tend to be left behind when water evaporates from the ocean surfaces, the remaining ocean water becomes progressively enriched in oxygen 18. The degree of enrichment can be determined by analyzing ocean sediments of the period, because these sediments are composed of calcium carbonate shells of marine organisms, shells that were constructed with oxygen atoms drawn from the surrounding ocean. The higher the ratio of oxygen 18 to oxygen 16 in a sedimentary specimen, the more land ice there was when the sediment was laid down.

As an indicator of shifts in the Earth's climate, the isotope record has two advantages. First, it is a global record: there is remarkably little variation in isotope ratios in sedimentary specimens taken from different continental locations. Second, it is a more continuous record than that taken from rocks on land…

According to the passage, which of the following is true of the ratios of oxygen isotopes in ocean sediments?

(A) They indicate that sediments found during an ice age contain more calcium carbonate than sediments formed at other times.

(B) They are less reliable than the evidence from rocks on land in determining the volume of land ice.

(C) They can be used to deduce the relative volume of land ice that was present when the sediment was laid down.

(D) They are more unpredictable during an ice age than in other climatic conditions.

(E) They can be used to determine atmospheric conditions at various times in the past.

答案：C

答案解析

由题目中“ratios of oxygen isotopes in ocean sediments”的意思可定位到“A recent discovery makes such a determination possible: relative land-ice volume for a given period can be deduced from the ratio of two oxygen isotopes, 16 and 18, found in ocean sediments”，由此比较容易选出答案C“它们能够用来推断出沉淀物在被堆积时陆地上的冰的

数量”，该选项只是将原文的句子顺序“A can be deduced from B”改成了“B can be used to deduce A”。

其他选项意思分别为：

A.它们表明，相对于其他时间形成的沉积物来说，冰川时期的沉积物含有更多的碳酸钙。

B.它们在确定陆地冰的数量方面，没有从陆地上的岩石中获得的证据可靠。

D.相对于在其他气候环境下，它们在冰川时期更加不可预测。

E.它们能够被用来确定以往不同时期的大气状况。