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The origin of the theory that major geologic events may occur at regular intervals can be traced back not to a study of volcanism or plate tectonics but to an investigation of marine extinctions. In the early 1980`s, scientists began to look closely at the question of how these extinctions occur. Two paleontologists, Raup and Sepkoski, compiled amaster list of marine species that died out duringthe past 268 million years and noted that there were brief periods during which many species disappeared at once. These mass extinc- tions occurred at surprisingly regular intervals.
Later studies revealed that extinctions of terrestrial reptiles and mammals also occurred periodically.
These findings, combined with the research of Raup and Sepkoski, led scientists to hypothesize the existence of some kind of cyclically recurring force powerful enough to affect living things profoundly. Speculation that so powerful a force might affect gelogic events as well led geologists to search for evidence of periodicity in episodes of volcanism, seafloor spreading, and plate movement.
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[阅读&逻辑 ]新版冲分救命题 -11894
Select the sentence that presents a conventional requirement that is rejected by the author of the passage.
[阅读&逻辑 ]精选题 -11861
Which of the following, if true of the cave, most weakens the argument?
[阅读&逻辑 ]精选题 -11860
It can be inferred that the “sediments
[阅读&逻辑 ]精选题 -11859
Which of the following best describes the issue raised by the question in the highlighted portion of the passage?
[阅读&逻辑 ]精选题 -11858
It can be inferred that which of the following is true of the “geologic evidence”?
[阅读&逻辑 ]精选题 -11857
Which of the following elements in the debate over the origin of Varanus is NOT provided in the passage?
[阅读&逻辑 ]精选题 -11856
It can be inferred from the passage that the geographical distribution of the Komodo dragon is
[阅读&逻辑 ]精选题 -11855
Which of the following, if discovered to be true, would most tend to suggest that the “correlation” mentioned in the passage held true for the people of the West Branch site?
[阅读&逻辑 ]精选题 -11854
The final sentence of the passage primarily serves to do which of the following?
[阅读&逻辑 ]精选题 -11853
The passage implies which of the following about beavers?
[阅读&逻辑 ]精选题 -11852
The passage provides support for which of the following statements about beaver dams?
[阅读&逻辑 ]精选题 -11851
According to the passage, which of the following best accounts for the apparent bias in antelope-migration direction?
[阅读&逻辑 ]精选题 -11850
The author of the passage implies that during the
[阅读&逻辑 ]精选题 -11849
According to the passage, which of the following is true of an Eurasia-Africa land bridge during ice ages?
[填空 ]精选题 -11843
The political upheaval caught most people by surprise: despite the ______ warning of some commentators, it had never seemed that imminent.
[填空 ]精选题 -11842
Even if the story now seems a surprisingly innocuous overture to the author’s later, more fully developed narrations, it ____ some of the key traits of those bleaker tales.
[填空 ]精选题 -11841
William Perkins, his ______ speaking style notwithstanding, has long been seen as the moderate face of his political party.
[填空 ]精选题 -11840
Just because, as a photographer, Friedlander (i)____ places that most people consider ugly does not mean that he is out to prove they are beautiful. Instead, his work suggests that the photographer simply cannot ignore so much of the built American landscape but is obligated to (ii)_____ what we pass through day in and day out, regardless of (iii)_____.
[填空 ]精选题 -11839
In the search for truth, the knowledge gained by scientists consists of approximations with varying degrees of certainty. Such (i)_____ truth can be highly (ii)_____, as the rapid and relatively steady progress of medical knowledge well exemplifies.
[填空 ]精选题 -11838
History teaches us that science is not _________ enterprise, indeed, it is quite the opposite, a motley assortment of tools designed to safeguard researchers against their own biases.
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