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  3. In 1831 when Smith was finally recognized by the Geological Society of London as the "father of English geology," it was not onl

In 1831 when Smith was finally recognized by the Geological Society of London as the "father of English geology," it was not onl

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问题     In 1831 when Smith was finally recognized by the Geological Society of London as the "father of English geology," it was not only for his maps but also for something even more important. Ever since people had begun to catalog the strata in particular outcrops, there had been the hope that these could somehow be used to calculate geological time. But as more and more accumulations of strata were cataloged in more and more places, it became clear that the sequences of rocks sometimes differed from region to region and that no rock type was ever going to become a reliable time marker throughout the world. Even without the problem of regional differences, rocks present a difficulty as unique time markers. Quartz is quartz—a silicon ion surrounded by four oxygen ions—there’s no difference at all between two-million-year-old Pleistocene quartz and Cambrian quartz created over 500 million years ago.
Why does the author use the phrase "Quartz is quartz"?
选项 A、To describe how the differences between Pleistocene and Cambrian quartz reveal information about dating rocks
B、To point out that the chemical composition of quartz makes it more difficult to date than other rocks
C、To provide an example of how regional differences in rock sequences can make a particular rock difficult to date
D、To explain that rocks are difficult to use for dating because their chemical compositions always remain the same over time
答案D
解析
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