GRE阅读高频机经原文及答案：地球冷暖周期
<p> 21. 地球冷暖周期通过石头含铁量推定 新题</p><p> <span word="Recent">Recent</span> <span word="studies">studies</span> <span word="of">of</span> <span word="sediment">sediment</span> <span word="in">in</span> <span word="the">the</span> <span word="North">North</span> <span word="Atlantics">Atlantics</span> <span word="deepwaters">deepwaters</span> <span word="reveal">reveal</span> <span word="possible">possible</span> <span word="cyclical">cyclical</span> <span word="patterns">patterns</span> <span word="in">in</span> <span word="the">the</span> <span word="history">history</span> <span word="of">of</span> <span word="Earths">Earths</span> <span word="climate">climate</span>. <span word="Therock">Therock</span> <span word="fragments">fragments</span> <span word="in">in</span> <span word="these">these</span> <span word="sediments">sediments</span> <span word="are">are</span> <span word="too">too</span> <span word="large">large</span> <span word="to">to</span> <span word="have">have</span> <span word="been">been</span> <span word="transported">transported</span> <span word="thereby">thereby</span> <span word="ocean">ocean</span> <span word="currents">currents</span>; <span word="they">they</span> <span word="must">must</span> <span word="have">have</span> <span word="reached">reached</span> <span word="their">their</span> <span word="present">present</span> <span word="locations">locations</span> <span word="by">by</span> <span word="travelingin">travelingin</span> <span word="large">large</span> <span word="icebergs">icebergs</span> <span word="that">that</span> <span word="floated">floated</span> <span word="long">long</span> <span word="distances">distances</span> <span word="from">from</span> <span word="their">their</span> <span word="point">point</span> <span word="of">of</span> <span word="origin">origin</span> <span word="beforemelting">beforemelting</span>.</p><p> <span word="Geologist">Geologist</span> <span word="Gerard">Gerard</span> <span word="Bond">Bond</span> <span word="noticed">noticed</span> <span word="that">that</span> <span word="some">some</span> <span word="of">of</span> <span word="the">the</span> <span word="sedimentgrains">sedimentgrains</span> <span word="were">were</span> <span word="stained">stained</span> <span word="with">with</span> <span word="ironoxide">ironoxide</span>, <span word="evidence">evidence</span> <span word="that">that</span> <span word="they">they</span> <span word="originated">originated</span> <span word="in">in</span> <span word="localeswhere">localeswhere</span> <span word="glaciers">glaciers</span> <span word="had">had</span> <span word="overrun">overrun</span> <span word="outcrops">outcrops</span> <span word="of">of</span> <span word="red">red</span> <span word="sandstone">sandstone</span>. <span word="Bonds">Bonds</span> <span word="detailed">detailed</span> <span word="analysisof">analysisof</span> <span word="deep">deep</span>-<span word="water">water</span> <span word="sediment">sediment</span> <span word="cores">cores</span> <span word="showed">showed</span> <span word="changes">changes</span> <span word="in">in</span> <span word="the">the</span> <span word="mix">mix</span> <span word="of">of</span> <span word="sediment">sediment</span> <span word="sources">sources</span> <span word="overtime">overtime</span>: <span word="the">the</span> <span word="proportion">proportion</span> <span word="of">of</span> <span word="these">these</span> <span word="red">red</span>-<span word="stained">stained</span> <span word="grains">grains</span> <span word="fluctuated">fluctuated</span> <span word="back">back</span> <span word="and">and</span> <span word="forth">forth</span> <span word="fromlows">fromlows</span> <span word="of">of</span> 5 <span word="percent">percent</span> <span word="to">to</span> <span word="highs">highs</span> <span word="of">of</span> <span word="about">about</span> 17 <span word="percent">percent</span>, <span word="and">and</span> <span word="these">these</span> <span word="fluctuations">fluctuations</span> <span word="occurredin">occurredin</span> <span word="a">a</span> <span word="nearly">nearly</span> <span word="regular">regular</span> 1,500-<span word="year">year</span> <span word="cycle">cycle</span>.</p><p> <span word="Bond">Bond</span> <span word="hypothesized">hypothesized</span> <span word="that">that</span> <span word="the">the</span> <span word="alternating">alternating</span> <span word="cycles">cycles</span> <span word="might">might</span> <span word="beevidence">beevidence</span> <span word="of">of</span> <span word="changes">changes</span> <span word="in">in</span> <span word="ocean">ocean</span>-<span word="water">water</span> <span word="circulation">circulation</span> <span word="and">and</span> <span word="therefore">therefore</span> <span word="in">in</span> <span word="Earthsclimate">Earthsclimate</span>. <span word="He">He</span> <span word="knew">knew</span> <span word="that">that</span> <span word="the">the</span> <span word="sources">sources</span> <span word="of">of</span> <span word="the">the</span> <span word="red">red</span>-<span word="stained">stained</span> <span word="grains">grains</span> <span word="were">were</span> <span word="generallycloser">generallycloser</span> <span word="to">to</span> <span word="the">the</span> <span word="North">North</span> <span word="Pole">Pole</span> <span word="than">than</span> <span word="were">were</span> <span word="the">the</span> <span word="places">places</span> <span word="yielding">yielding</span> <span word="a">a</span> <span word="high">high</span> <span word="proportion">proportion</span> <span word="ofclean">ofclean</span> <span word="grains">grains</span>. <span word="At">At</span> <span word="certain">certain</span> <span word="times">times</span>, <span word="apparently">apparently</span>, <span word="more">more</span> <span word="icebergs">icebergs</span> <span word="from">from</span> <span word="the">the</span> <span word="ArcticOcean">ArcticOcean</span> <span word="in">in</span> <span word="the">the</span> <span word="far">far</span> <span word="north">north</span> <span word="were">were</span> <span word="traveling">traveling</span> <span word="south">south</span> <span word="well">well</span> <span word="into">into</span> <span word="the">the</span> <span word="North">North</span> <span word="Atlantic">Atlantic</span> <span word="beforemelting">beforemelting</span> <span word="and">and</span> <span word="shedding">shedding</span> <span word="their">their</span> <span word="sediment">sediment</span>. <span word="Ocean">Ocean</span> <span word="waters">waters</span> <span word="are">are</span> <span word="constantly">constantly</span> <span word="moving">moving</span>, <span word="andwater">andwater</span> <span word="temperature">temperature</span> <span word="is">is</span> <span word="both">both</span> <span word="a">a</span> <span word="cause">cause</span> <span word="and">and</span> <span word="an">an</span> <span word="effect">effect</span> <span word="of">of</span> <span word="this">this</span> <span word="movement">movement</span>. <span word="As">As</span> <span word="watercools">watercools</span>, <span word="it">it</span> <span word="becomes">becomes</span> <span word="denser">denser</span> <span word="and">and</span> <span word="sinks">sinks</span> <span word="to">to</span> <span word="the">the</span> <span word="oceans">oceans</span> <span word="bottom">bottom</span>. <span word="During">During</span> <span word="some">some</span> <span word="periods">periods</span>,<span word="the">the</span> <span word="bottom">bottom</span> <span word="layer">layer</span> <span word="of">of</span> <span word="the">the</span> <span word="worlds">worlds</span> <span word="oceans">oceans</span> <span word="comes">comes</span> <span word="from">from</span> <span word="cold">cold</span>, <span word="dense">dense</span> <span word="water">water</span> <span word="sinking">sinking</span> <span word="inthe">inthe</span> <span word="far">far</span> <span word="North">North</span> <span word="Atlantic">Atlantic</span>. <span word="This">This</span> <span word="causes">causes</span> <span word="the">the</span> <span word="warm">warm</span> <span word="surface">surface</span> <span word="waters">waters</span> <span word="of">of</span> <span word="the">the</span> <span word="Gulf">Gulf</span> <span word="Streamto">Streamto</span> <span word="be">be</span> <span word="pulled">pulled</span> <span word="northward">northward</span>. <span word="Bond">Bond</span> <span word="realized">realized</span> <span word="that">that</span> <span word="during">during</span> <span word="such">such</span> <span word="periods">periods</span>, <span word="the">the</span> <span word="influx">influx</span> <span word="ofthese">ofthese</span> <span word="warm">warm</span> <span word="surface">surface</span> <span word="waters">waters</span> <span word="into">into</span> <span word="northern">northern</span> <span word="regions">regions</span> <span word="could">could</span> <span word="cause">cause</span> <span word="a">a</span> <span word="large">large</span> <span word="proportionof">proportionof</span> <span word="the">the</span> <span word="icebergs">icebergs</span> <span word="that">that</span> <span word="bear">bear</span> <span word="red">red</span> <span word="grains">grains</span> <span word="to">to</span> <span word="melt">melt</span> <span word="before">before</span> <span word="traveling">traveling</span> <span word="very">very</span> <span word="far">far</span> <span word="into">into</span> <span word="theNorth">theNorth</span> <span word="Atlantic">Atlantic</span>. <span word="But">But</span> <span word="sometimes">sometimes</span> <span word="the">the</span> <span word="oceans">oceans</span> <span word="dynamic">dynamic</span> <span word="changes">changes</span>, <span word="and">and</span> <span word="waters">waters</span> <span word="from">from</span> <span word="theGulf">theGulf</span> <span word="Stream">Stream</span> <span word="do">do</span> <span word="not">not</span> <span word="travel">travel</span> <span word="northward">northward</span> <span word="in">in</span> <span word="this">this</span> <span word="way">way</span>. <span word="During">During</span> <span word="these">these</span> <span word="periods">periods</span>, <span word="surfacewaters">surfacewaters</span> <span word="in">in</span> <span word="the">the</span> <span word="North">North</span> <span word="Atlantic">Atlantic</span> <span word="would">would</span> <span word="generally">generally</span> <span word="be">be</span> <span word="colder">colder</span>, <span word="permitting">permitting</span> <span word="icebergsbearing">icebergsbearing</span> <span word="red">red</span>-<span word="stained">stained</span> <span word="grains">grains</span> <span word="to">to</span> <span word="travel">travel</span> <span word="farther">farther</span> <span word="south">south</span> <span word="in">in</span> <span word="the">the</span> <span word="North">North</span> <span word="Atlantic">Atlantic</span> <span word="beforemelting">beforemelting</span> <span word="and">and</span> <span word="depositing">depositing</span> <span word="their">their</span> <span word="sediment">sediment</span>.</p>
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