One of the first recorded observers to surmise a long age for Earth was the Greek historian Herodotus, who lived from approximately 480 B.C. to 425 B.C. He observed that the Nile River Delta was in fact a series of sediment deposits built up in successive floods. By noting that individual floods deposit only thin layers of sediment, he was able to conclude that the Nile Delta had taken many thousands of years to build up. More important than the amount of time Herodotus computed, which turns out to be trivial compared with the age of Earth, was the notion that one could estimate ages of geologic features by determining rates of the processes responsible for such features, and then assuming the rates to be roughly constant over time. Similar applications of this concept were to be used again and again in later centuries to estimate the ages of rock formations and, in particular, of layers of sediment that had compacted and cemented to form sedimentary rocks.

It was not until the seventeenth century that attempts were made again to understand clues to Earth's history through the rock record. Nicolaus Steno (1638-1686) was the first to work out principles of the progressive depositing of sediment in Tuscany. However, James Hutton (1726-1797), known as the founder of modern geology, was the first to have the important insight that geologic processes are cyclic in nature. Forces associated with subterranean heat cause land to be uplifted into plateaus and mountain ranges. The effects of wind and water then break down the masses of uplifted rock, producing sediment that is transported by water downward to ultimately form layers in lakes, seashores, or even oceans. Over time, the layers become sedimentary rock. These rocks are then uplifted sometime in the future to form new mountain ranges, which exhibit the sedimentary layers (and the remains of life within those layers) of the earlier episodes of erosion and deposition.

Hutton's concept represented a remarkable insight because it unified many individual phenomena and observations into a conceptual picture of Earth’s history. With the further assumption that these geologic processes were generally no more or less vigorous than they are today, Hutton's examination of sedimentary layers led him to realize that Earth's history must be enormous, that geologic time is an abyss and human history a speck by comparison.

After Hutton, geologists tried to determine rates of sedimentation so as to estimate the age of Earth from the total length of the sedimentary or stratigraphic record. Typical numbers produced at the turn of the twentieth century were 100 million to 400 million years. These underestimated the actual age by factors of 10 to 50 because much of the sedimentary record is missing in various locations and because there is a long rock sequence that is older than half a billion years that is far less well defined in terms of fossils and less well preserved.

Various other techniques to estimate Earth's age fell short, and particularly noteworthy in this regard were flawed determinations of the Sun's age. It had been recognized by the German philosopher Immanuel Kant (1724-1804) that chemical reactions could not supply the tremendous amount of energy flowing from the Sun for more than about a millennium. Two physicists during the nineteenth century both came up with ages for the Sun based on the Sun's energy coming from gravitational contraction. Under the force of gravity, the compression resulting from a collapse of the object must release energy. Ages for Earth were derived that were in the tens of millions of years, much less than the geologic estimates of the lime.

It was the discovery of radioactivity at the end of the nineteenth century that opened the door to determining both the Sun’s energy source and the age of Earth. From the initial work came a suite of discoveries leading to radio isotopic dating, which quickly led to the realization that Earth must be billions of years old, and to the discovery of nuclear fusion as an energy source capable of sustaining the Sun's luminosity for that amount of time. By the 1960s, both analysis of meteorites and refinements of solar evolution models converged on an age for the solar system, and hence for Earth, of 4.5 billion years.

Questions:
question_stem: The word "trivial" in the passage is closest in meaning to
choices: tag: A
text: similar

tag: B
text: inaccurate

tag: C
text: small

tag: D
text: significant
answer_key: C
explanation: 本题为词汇题，根据所给单词trivial定位到第一段More important than the amount of time Herodotus computed, which turns out to be trivial compared with the age of Earth, was the notion that one could estimate ages of geologic features by determining rates of the processes responsible for such features, and then assuming the rates to be roughly constant over time.本句大致意思为：与地球的年龄相比，Herodotus计算出来的时间量是trivial的，与其相比更重要的是一个概念，这个概念是一个人可以通过估计相应地理特征的某种过程的速度来估计地理特征的年龄……再以Herodotus为关键词定位这个time是什么，找到本段第三句，发现他是推测Nile Delta花了几千年形成的。根据常识，我们知道一个三角洲的年龄是不能跟古老的地球相比的，是远小于地球年龄的。这时候回到题目看选项，A相似的，B不准确的，C小的，D重要的，选C。

question_stem: According to paragraph 1, Herodotus' observations of the Nile River Delta were significant because they allowed him to
choices: tag: A
text: provide detailed records of the most significant floods in the history of the Nile

tag: B
text: develop a way of calculating the age of geologic features

tag: C
text: conclude that the Nile River Delta was as old as Earth

tag: D
text: predict when the river would flood and when it would not
answer_key: B
explanation: 先看题干：Herodotus这个人对于三角洲的观察为什么是重要的呢？抓出关键词Herodotus，Delta和significant回原文第一段定位。第一段第四句也就是我们第一题里分析过的那句同时出现了这三个关键词——需要考生关注的是significant并没有原样出现，而是通过important同义替换了。考生在关键词定位时注意不要只看题干里出现的词，要注意原文中出现同义替换的地方，这往往就是答案所在。再次复习下这一句的意思，这次我们把修饰的从句剃掉，直接抓出主干：More important than the amount of time Herodotus computed, was the notion. 与Herodotus计算出的数值相比，有个概念更重要。再细看，这个notion是什么呢？one could estimate ages of geologic features by determining rates of the processes responsible for such features, and then assuming the rates to be roughly constant over time.本句大致意思是：一个人可以通过一些方法来估计地理特征的年龄。理解原文到这个程度后，我们返回题目，看看四个选项：A 提供了关于什么什么的具体的记录，本句里没有，排除；B 发现了一种计算地理特征的年龄，对了；C 推测出这个三角洲跟地球一样老，胡说八道；D 推测这个河流什么时候泛滥，原句没提。选B。

question_stem: According to paragraph 2, James Hutton was the first person to
choices: tag: A
text: understand clues to Earth's history through the rock record.

tag: B
text: work out principles of the progressive depositing of sediment.

tag: C
text: realize that geologic processes happen in cycles.

tag: D
text: describe the forces associated with subterranean heat.
answer_key: C
explanation: 先看题干，抓出关键词James Hutton和first person。根据题目指示找到原文第二段，根据关键词定位。However, James Hutton (1726-1797), known as the founder of modern geology, was the first to have the important insight that geologic processes are cyclic in nature. 这一句里两个关键词同时出现。本句主干的大致句意是：James Hutton这个人是第一个发现地理过程在自然界是循环往复的。接下来回到题目，A通过岩石记录发现地球历史的线索，没提；B发现了沉积物逐渐分解的原理，也没提；C 发现地理过程循环发生，对了；D 描述了一个跟什么热量相关的力，跟原文没什么关系。选C。

question_stem: The word "exhibit" in the passage is closest in meaning to
choices: tag: A
text: replace

tag: B
text: show

tag: C
text: cover

tag: D
text: expand
answer_key: B
explanation: 本题又是词汇题，解题套路与第一题相似。定位到第二段：These rocks are then uplifted sometime in the future to form new mountain ranges, which exhibit the sedimentary layers. exhibit这个词的意思指的是“展示、展现、显现”与show意思相近，因此选择B。

question_stem: According to paragraph 3, Hutton's insight about Earth’s history was significant because it
choices: tag: A
text: provided a conceptual framework for understanding Earth's past.

tag: B
text: showed that human history is insignificant in comparison with Earth's history.

tag: C
text: suggested that Earth’s history is much older than previously thought.

tag: D
text: emphasized that geologic processes happen cyclically.
answer_key: A
explanation: 本题考察对第三段的理解。根据第三段最后一句Hutton's concept represented a remarkable insight because it unified many individual phenomena and observations into a conceptual picture of Earth’s history. 这句话可以推测出答案是A，提供了一个理解地球过去的概念框架。B选项提到人类历史的微不足道，原文并没有强调这个观点；C选项说地球历史比之前认为的要久，这句话并没有直接表达；D选项提到地质过程是循环的，第三段没有提到这一点。

question_stem: According to paragraph 4, why were early estimates of Earth’s age too low?
choices: tag: A
text: Most of the sedimentary record is missing in certain places.

tag: B
text: There were no fossil records in the oldest rock formations.

tag: C
text: The calculations were based on incomplete or incorrect assumptions.

tag: D
text: The amount of sedimentation was much slower than originally thought.
answer_key: A
explanation: 定位到第四段，第一句提到地质学家在估算地球年龄时，认为沉积层记录从100百万到400百万年之间，但由于沉积记录在某些地方是缺失的，因此估算的结果被低估了。选A。

question_stem: According to paragraph 5, why were early determinations of the Sun’s age too low?
choices: tag: A
text: Chemical reactions could not have produced enough energy for such a long time.

tag: B
text: The Sun’s energy source was misidentified.

tag: C
text: The Sun’s energy was misunderstood to come from gravitational contraction.

tag: D
text: The Sun’s energy output was thought to be much greater than it actually is.
answer_key: C
explanation: 定位到第五段，提到Kant认为化学反应无法为太阳提供足够的能量，紧接着说两位物理学家误以为太阳的能量来自于重力收缩，从而低估了太阳的年龄。选C。

question_stem: According to paragraph 6, what was the significance of the discovery of radioactivity for estimating the age of Earth?
choices: tag: A
text: It led to the discovery of the Sun’s energy source.

tag: B
text: It opened the door to radio isotopic dating.

tag: C
text: It revealed that Earth’s age could not be determined from sedimentary records.

tag: D
text: It provided a more accurate way to estimate the Sun’s age.
answer_key: B
explanation: 定位到第六段最后一句，提到放射性发现带来了放射性同位素测定的技术，使我们能够估算地球的年龄。选B。

question_stem: The passage primarily discusses
choices: tag: A
text: methods used to determine the age of Earth.

tag: B
text: different theories about the Sun's age.

tag: C
text: the history of the Earth’s geological processes.

tag: D
text: the development of geological ideas over time.
answer_key: D
explanation: 这道主旨题定位到文章最后一句：By the 1960s, both analysis of meteorites and refinements of solar evolution models converged on an age for the solar system, and hence for Earth, of 4.5 billion years.整篇文章主要描述了关于地球年龄的不同理论和估算方法，从希腊历史学家赫罗多托斯到19世纪末发现放射性，几乎涵盖了所有的地质历史进程。选D。