Attempts at Determining Earth’s Age Since the dawn of civilization, people have been curious about the age of Earth. In addition, we have not been satisfied in being able to sate merely the relative geologic age of a rock or fossil. Human curiosity demands that we know actual age in years. Geologists working during the nineteenth century understood rock bodies, they would have to concentrate on natural processes that continue at a constant rate and that also leave some sort of tangible record in the rocks. Evolution is one such process, and geologist Charles Lyell (1797-1875)recognized this. [■]By comparing the amount of evolution exhibited by marine mollusks then, Lyell estimated that 80 million years had elapsed since the beginning of the Tertiary Period. He came astonishingly close to the mark, since it was actually about 65 million years. [■]However, for older sequence of evolutionary development, estimates based on parts in the fossil record. [■] Rates of evolution for many orders of plants and animals were not well understood. [■] 1. The word “tangible” in the passage is closest in meaning to（ ） A. physical B. related C. significant D. helpful 2. It can be inferred form paragraph 2 that Charles Lyell based his study of the marine mollusk fossils on which of the following assumptions?（ ） A. The Tertiary Period was separated into division of time that were equal in length. B. Mollusks lived under rocks in the sea during the Tertiary period. C. Evolution of mollusks proceeded at a uniform rate over time D. Mollusks have evolved less rapidly with the passing of time 3. According to paragraph 2, Lyell's strategy for estimation geologic dates was not very accurate for periods before the Tertiary Period party because（ ） A. Marine mollusks did not evolve until the Tertiary Period B. fossil records of the very distant past are incomplete C. there was not much agreement about how to identify or categorize earlier eras D. the duration of previous geologic periods was difficult to determine 13. Look at the four squares [■] that indicate where the following sentence could be added to the passage. More fundamentally, Lyell's evolutionary approach is intrinsically limited because Earth existed long before life and evolution began. Where would the sentence best fit?（ ） In another attempt, geologists reasoned that if rates of deposition could be determined for sedimentary rocks, they might be able to estimate the time required for deposition of a given thickness of strata, or rock layers. Similar reasoning suggested that one could estimate total elapsed geologic time by dividing the average thickness of sediment transported annually to the oceans into the total thickness of sedimentary rock that had ever been deposited in the past. Unfortunately, such estimates did not adequately account for past difference in r...
