为何马里亚纳海沟成为了地球上最深的地方
<p><span word="James">James</span> <span word="Cameron">Cameron</span> <span word="made">made</span> <span word="headlines">headlines</span> <span word="in">in</span> <span word="March">March</span> <span word="by">by</span> <span word="successfully">successfully</span> <span word="diving">diving</span> 6.8 <span word="miles">miles</span> (11 <span word="kilometers">kilometers</span>) <span word="to">to</span> <span word="the">the</span> <span word="deepest">deepest</span> <span word="part">part</span> <span word="of">of</span> <span word="the">the</span> <span word="Mariana">Mariana</span> <span word="Trench">Trench</span> <span word="in">in</span> <span word="a">a</span> <span word="one">one</span>-<span word="person">person</span> <span word="submersible">submersible</span> <span word="called">called</span> <span word="the">the</span> <span word="Deepsea">Deepsea</span> <span word="Challenger">Challenger</span>. <span word="Best">Best</span> <span word="known">known</span> <span word="as">as</span> <span word="a">a</span> <span word="Hollywood">Hollywood</span> <span word="director">director</span>, <span word="Cameron">Cameron</span> <span word="is">is</span> <span word="one">one</span> <span word="of">of</span> <span word="just">just</span> <span word="three">three</span> <span word="people">people</span> <span word="to">to</span> <span word="dive">dive</span> <span word="to">to</span> <span word="Earth">Earth</span>’<span word="s">s</span> <span word="deepest">deepest</span> <span word="point">point</span>, <span word="and">and</span> <span word="the">the</span> <span word="only">only</span> <span word="one">one</span> <span word="to">to</span> <span word="be">be</span> <span word="able">able</span> <span word="to">to</span> <span word="stay">stay</span> <span word="long">long</span> <span word="enough">enough</span> <span word="to">to</span> <span word="look">look</span> <span word="around">around</span>. <span word="Though">Though</span> <span word="Cameron">Cameron</span> <span word="and">and</span> <span word="his">his</span> <span word="team">team</span> <span word="are">are</span> <span word="hoping">hoping</span> <span word="to">to</span> <span word="discover">discover</span> <span word="more">more</span> <span word="about">about</span> <span word="the">the</span> <span word="biology">biology</span> <span word="of">of</span> <span word="the">the</span> <span word="Mariana">Mariana</span> <span word="depths">depths</span>, <span word="geologists">geologists</span> <span word="already">already</span> <span word="know">know</span> <span word="a">a</span> <span word="lot">lot</span> <span word="about">about</span> <span word="how">how</span> <span word="the">the</span> <span word="Mariana">Mariana</span> <span word="Trench">Trench</span> <span word="formed">formed</span>—<span word="and">and</span> <span word="why">why</span> <span word="it">it</span>’<span word="s">s</span> <span word="Earth">Earth</span>’<span word="s">s</span> <span word="deepest">deepest</span> <span word="spot">spot</span>.</p><p><span word="Three">Three</span> <span word="Major">Major</span> <span word="Factors">Factors</span> <span word="that">that</span> <span word="Made">Made</span> <span word="Earth">Earth</span>’<span word="s">s</span> <span word="Deepest">Deepest</span> <span word="Spot">Spot</span></p><p><span word="The">The</span> <span word="Mariana">Mariana</span> <span word="Trench">Trench</span> <span word="isn">isn</span>’<span word="t">t</span> <span word="really">really</span> <span word="the">the</span> <span word="deep">deep</span>, <span word="narrow">narrow</span> <span word="furrow">furrow</span> <span word="that">that</span> <span word="the">the</span> <span word="word">word</span> “<span word="trench">trench</span>” <span word="implies">implies</span>. <span word="Rather">Rather</span>, <span word="the">the</span> <span word="abyss">abyss</span> <span word="marks">marks</span> <span word="the">the</span> <span word="location">location</span> <span word="of">of</span> <span word="a">a</span> <span word="subduction">subduction</span> <span word="zone">zone</span>. <span word="Subduction">Subduction</span> <span word="zones">zones</span> <span word="occur">occur</span> <span word="where">where</span> <span word="one">one</span> <span word="part">part</span> <span word="of">of</span> <span word="the">the</span> <span word="seabed">seabed</span>—<span word="in">in</span> <span word="this">this</span> <span word="case">case</span> <span word="the">the</span> <span word="Pacific">Pacific</span> <span word="plate">plate</span>—<span word="dives">dives</span> <span word="beneath">beneath</span> <span word="another">another</span>, <span word="the">the</span> <span word="Philippine">Philippine</span> <span word="plate">plate</span>. <span word="Tectonic">Tectonic</span> <span word="forces">forces</span> <span word="eventually">eventually</span> <span word="make">make</span> <span word="the">the</span> <span word="Pacific">Pacific</span> <span word="plate">plate</span> <span word="dive">dive</span> <span word="into">into</span> <span word="the">the</span> <span word="Earth">Earth</span>’<span word="s">s</span> <span word="interior">interior</span> <span word="almost">almost</span> <span word="vertically">vertically</span>, <span word="but">but</span> <span word="at">at</span> <span word="seabed">seabed</span> <span word="level">level</span> <span word="the">the</span> <span word="plate">plate</span> <span word="dips">dips</span> <span word="at">at</span> <span word="a">a</span> <span word="relatively">relatively</span> <span word="gentle">gentle</span> <span word="angle">angle</span>.</p><p><span word="Robert">Robert</span> <span word="Stern">Stern</span>, <span word="a">a</span> <span word="geophysicist">geophysicist</span> <span word="at">at</span> <span word="the">the</span> <span word="University">University</span> <span word="of">of</span> <span word="Texas">Texas</span>, <span word="said">said</span>, “<span word="One">One</span> <span word="reason">reason</span> <span word="the">the</span> <span word="Mariana">Mariana</span> <span word="Trench">Trench</span> <span word="is">is</span> <span word="so">so</span> <span word="deep">deep</span> <span word="is">is</span> <span word="because">because</span> <span word="the">the</span> <span word="western">western</span> <span word="Pacific">Pacific</span> <span word="is">is</span> <span word="home">home</span> <span word="to">to</span> <span word="some">some</span> <span word="of">of</span> <span word="the">the</span> <span word="oldest">oldest</span> <span word="seafloor">seafloor</span> <span word="in">in</span> <span word="the">the</span> <span word="world">world</span>—<span word="about">about</span> 180 <span word="million">million</span> <span word="years">years</span> <span word="old">old</span>. <span word="Seafloor">Seafloor</span> <span word="is">is</span> <span word="formed">formed</span> <span word="as">as</span> <span word="lava">lava</span> <span word="at">at</span> <span word="mid">mid</span>-<span word="ocean">ocean</span> <span word="ridges">ridges</span>. <span word="When">When</span> <span word="it">it</span>’<span word="s">s</span> <span word="fresh">fresh</span>, <span word="lava">lava</span> <span word="is">is</span> <span word="comparatively">comparatively</span> <span word="warm">warm</span> <span word="and">and</span> <span word="buoyant">buoyant</span>, <span word="riding">riding</span> <span word="high">high</span> <span word="on">on</span> <span word="the">the</span> <span word="underlying">underlying</span> <span word="mantle">mantle</span>. <span word="But">But</span> <span word="as">as</span> <span word="lava">lava</span> <span word="ages">ages</span> <span word="and">and</span> <span word="spreads">spreads</span> <span word="away">away</span> <span word="from">from</span> <span word="its">its</span> <span word="source">source</span>, <span word="it">it</span> <span word="slowly">slowly</span> <span word="cools">cools</span> <span word="and">and</span> <span word="becomes">becomes</span> <span word="increasingly">increasingly</span> <span word="dense">dense</span>, <span word="causing">causing</span> <span word="it">it</span> <span word="to">to</span> <span word="settle">settle</span> <span word="ever">ever</span> <span word="lower">lower</span>—<span word="as">as</span> <span word="is">is</span> <span word="the">the</span> <span word="case">case</span> <span word="with">with</span> <span word="the">the</span> <span word="Mariana">Mariana</span> <span word="Trench">Trench</span>.”</p>
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