gre考试阅读真题解析(B)
<p> <span word="The">The</span> <span word="origin">origin</span> <span word="of">of</span> <span word="the">the</span> <span word="theory">theory</span> <span word="that">that</span> <span word="major">major</span> <span word="geologic">geologic</span> <span word="events">events</span> <span word="may">may</span> <span word="occur">occur</span> <span word="at">at</span> <span word="regular">regular</span> <span word="intervals">intervals</span> <span word="can">can</span> <span word="be">be</span> <span word="traced">traced</span> <span word="back">back</span> <span word="not">not</span> <span word="to">to</span> <span word="a">a</span> <span word="study">study</span> <span word="of">of</span> <span word="volcanism">volcanism</span> <span word="or">or</span> <span word="plate">plate</span> <span word="tectonics">tectonics</span> <span word="but">but</span> <span word="to">to</span> <span word="an">an</span> <span word="investigation">investigation</span> <span word="of">of</span> <span word="marine">marine</span> <span word="extinctions">extinctions</span>. <span word="In">In</span> <span word="the">the</span> <span word="early">early</span> 1980<span word="s">s</span>, <span word="scientists">scientists</span> <span word="began">began</span> <span word="to">to</span> <span word="look">look</span> <span word="closely">closely</span> <span word="at">at</span> <span word="the">the</span> <span word="question">question</span> <span word="of">of</span> <span word="how">how</span> <span word="these">these</span> <span word="extinctions">extinctions</span> <span word="occur">occur</span>. <span word="Two">Two</span> <span word="paleontologists">paleontologists</span>, <span word="Raup">Raup</span> <span word="and">and</span> <span word="Sepkoski">Sepkoski</span>, <span word="compiled">compiled</span> <span word="a">a</span> <span word="master">master</span> <span word="list">list</span> <span word="of">of</span> <span word="marine">marine</span> <span word="species">species</span> <span word="that">that</span> <span word="died">died</span> <span word="out">out</span> <span word="during">during</span> <span word="the">the</span> <span word="past">past</span> 268 <span word="million">million</span> <span word="years">years</span> <span word="and">and</span> <span word="noted">noted</span> <span word="that">that</span> <span word="there">there</span> <span word="were">were</span> <span word="brief">brief</span> <span word="periods">periods</span> <span word="during">during</span> <span word="which">which</span> <span word="many">many</span> <span word="species">species</span> <span word="disappeared">disappeared</span> <span word="at">at</span> <span word="once">once</span>. <span word="These">These</span> <span word="mass">mass</span> <span word="extinctions">extinctions</span> <span word="occurred">occurred</span> <span word="at">at</span> <span word="surprisingly">surprisingly</span> <span word="regular">regular</span> <span word="intervals">intervals</span>.</p><p> <span word="Later">Later</span> <span word="studies">studies</span> <span word="revealed">revealed</span> <span word="that">that</span> <span word="extinctions">extinctions</span> <span word="of">of</span> <span word="terrestrial">terrestrial</span> <span word="reptiles">reptiles</span> <span word="and">and</span> <span word="mammals">mammals</span> <span word="also">also</span> <span word="occurred">occurred</span> <span word="periodically">periodically</span>. <span word="These">These</span> <span word="findings">findings</span>, <span word="combined">combined</span> <span word="with">with</span> <span word="the">the</span> <span word="research">research</span> <span word="of">of</span> <span word="Raup">Raup</span> <span word="and">and</span> <span word="Sepkoski">Sepkoski</span>, <span word="led">led</span> <span word="scientists">scientists</span> <span word="to">to</span> <span word="hypothesize">hypothesize</span> <span word="the">the</span> <span word="existence">existence</span> <span word="of">of</span> <span word="some">some</span> <span word="kind">kind</span> <span word="of">of</span> <span word="cyclically">cyclically</span> <span word="recurring">recurring</span> <span word="force">force</span> <span word="powerful">powerful</span> <span word="enough">enough</span> <span word="to">to</span> <span word="affect">affect</span> <span word="living">living</span> <span word="things">things</span> <span word="profoundly">profoundly</span>. <span word="Speculation">Speculation</span> <span word="that">that</span> <span word="so">so</span> <span word="powerful">powerful</span> <span word="a">a</span> <span word="force">force</span> <span word="might">might</span> <span word="affect">affect</span> <span word="geologic">geologic</span> <span word="events">events</span> <span word="as">as</span> <span word="well">well</span> <span word="led">led</span> <span word="geologists">geologists</span> <span word="to">to</span> <span word="search">search</span> <span word="for">for</span> <span word="evidence">evidence</span> <span word="of">of</span> <span word="periodicity">periodicity</span> <span word="in">in</span> <span word="episodes">episodes</span> <span word="of">of</span> <span word="volcanism">volcanism</span>, <span word="seafloor">seafloor</span> <span word="spreading">spreading</span>, <span word="and">and</span> <span word="plate">plate</span> <span word="movement">movement</span>.</p><p> 17. <span word="According">According</span> <span word="to">to</span> <span word="the">the</span> <span word="passage">passage</span>, <span word="Raup">Raup</span> <span word="and">and</span> <span word="Sepkoskis">Sepkoskis</span> <span word="research">research</span> <span word="was">was</span> <span word="concerned">concerned</span> <span word="with">with</span></p><p> <span word="learning">learning</span> <span word="more">more</span> <span word="about">about</span> <span word="the">the</span> <span word="habitats">habitats</span> <span word="of">of</span> <span word="marine">marine</span> <span word="species">species</span></p><p> <span word="studying">studying</span> <span word="plate">plate</span> <span word="tectonics">tectonics</span> <span word="and">and</span> <span word="the">the</span> <span word="occurrence">occurrence</span> <span word="of">of</span> <span word="volcanism">volcanism</span> <span word="over">over</span> <span word="the">the</span> <span word="past">past</span> 268 <span word="million">million</span> <span word="years">years</span></p><p> <span word="examining">examining</span> <span word="extinctions">extinctions</span> <span word="of">of</span> <span word="marine">marine</span> <span word="species">species</span> <span word="over">over</span> <span word="the">the</span> <span word="past">past</span> 268 <span word="million">million</span> <span word="years">years</span></p>
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