地球土著还是外星来客?
<p><span word="Life">Life</span> <span word="on">on</span> <span word="Earth">Earth</span> <span word="may">may</span> <span word="have">have</span> <span word="its">its</span> <span word="origins">origins</span> <span word="in">in</span> <span word="outer">outer</span> <span word="space">space</span>, <span word="according">according</span> <span word="to">to</span> <span word="NASA">NASA</span> <span word="research">research</span>. <span word="Scientists">Scientists</span> <span word="have">have</span> <span word="analysed">analysed</span> <span word="meteorites">meteorites</span> <span word="that">that</span> <span word="formed">formed</span> <span word="billions">billions</span> <span word="of">of</span> <span word="years">years</span> <span word="ago">ago</span> <span word="before">before</span> <span word="falling">falling</span> <span word="to">to</span> <span word="Earth">Earth</span>。</p><p><span word="The">The</span> <span word="carbon">carbon</span>-<span word="rich">rich</span> <span word="fragments">fragments</span> <span word="were">were</span> <span word="found">found</span> <span word="to">to</span> <span word="contain">contain</span> <span word="chemicals">chemicals</span> <span word="similar">similar</span> <span word="to">to</span> <span word="one">one</span> <span word="of">of</span> <span word="the">the</span> <span word="key">key</span> <span word="components">components</span> <span word="of">of</span> <span word="DNA">DNA</span>, <span word="the">the</span> <span word="building">building</span> <span word="blocks">blocks</span> <span word="of">of</span> <span word="life">life</span>。</p><p><span word="Tests">Tests</span> <span word="show">show</span> <span word="that">that</span> <span word="the">the</span> <span word="presence">presence</span> <span word="of">of</span> <span word="these">these</span> <span word="chemicals">chemicals</span> <span word="cannot">cannot</span> <span word="be">be</span> <span word="explained">explained</span> <span word="away">away</span> <span word="by">by</span> <span word="Earthly">Earthly</span> <span word="contamination">contamination</span>, <span word="suggesting">suggesting</span> <span word="DNA">DNA</span>’<span word="s">s</span> <span word="origins">origins</span> <span word="may">may</span> <span word="lie">lie</span> <span word="in">in</span> <span word="outer">outer</span> <span word="space">space</span>。</p><p><span word="The">The</span> <span word="study">study</span>/<span word="s">s</span> <span word="lead">lead</span> <span word="author">author</span>, <span word="Dr">Dr</span> <span word="Michael">Michael</span> <span word="Callahan">Callahan</span>, <span word="of">of</span> <span word="the">the</span> <span word="Nasa">Nasa</span> <span word="Goddard">Goddard</span> <span word="Space">Space</span> <span word="Flight">Flight</span> <span word="Centre">Centre</span> <span word="in">in</span> <span word="Maryland">Maryland</span>, <span word="said">said</span>: "<span word="With">With</span> <span word="meteorites">meteorites</span> <span word="and">and</span> <span word="comets">comets</span> <span word="impacting">impacting</span> <span word="the">the</span> <span word="early">early</span> <span word="Earth">Earth</span>, <span word="it">it</span> <span word="appears">appears</span> <span word="that">that</span> <span word="they">they</span> <span word="did">did</span> <span word="deliver">deliver</span> <span word="some">some</span> <span word="very">very</span> <span word="important">important</span> <span word="ingredients">ingredients</span>."</p><p><span word="Previous">Previous</span> <span word="studies">studies</span> <span word="found">found</span> <span word="meteorites">meteorites</span> <span word="harbour">harbour</span> <span word="the">the</span> <span word="other">other</span> <span word="two">two</span> <span word="of">of</span> <span word="the">the</span> <span word="three">three</span> <span word="basic">basic</span> <span word="ingredients">ingredients</span> <span word="of">of</span> <span word="life">life</span>. <span word="These">These</span> <span word="are">are</span> <span word="amino">amino</span> <span word="acids">acids</span>, <span word="the">the</span> "<span word="beads">beads</span>" <span word="that">that</span> <span word="form">form</span> <span word="proteins">proteins</span> <span word="when">when</span> <span word="strung">strung</span> <span word="together">together</span>, <span word="and">and</span> <span word="chemicals">chemicals</span> <span word="needed">needed</span> <span word="to">to</span> <span word="allow">allow</span> <span word="cells">cells</span> <span word="to">to</span> <span word="create">create</span> <span word="a">a</span> <span word="membrane">membrane</span> <span word="barrier">barrier</span>. <span word="The">The</span> <span word="chemicals">chemicals</span> <span word="in">in</span> <span word="DNA">DNA</span> <span word="are">are</span> <span word="the">the</span> <span word="third">third</span>。</p><p><span word="The">The</span> <span word="find">find</span> <span word="comes">comes</span> <span word="from">from</span> <span word="US">US</span> <span word="scientists">scientists</span>, <span word="predominantly">predominantly</span> <span word="NASA">NASA</span> <span word="researchers">researchers</span>, <span word="who">who</span> <span word="analysed">analysed</span> <span word="the">the</span> <span word="chemical">chemical</span> <span word="make">make</span>-<span word="up">up</span> <span word="of">of</span> 12 <span word="meteorites">meteorites</span>。</p><p><span word="Writing">Writing</span> <span word="in">in</span> <span word="the">the</span> <span word="journal">journal</span> <span word="Proceedings">Proceedings</span> <span word="of">of</span> <span word="the">the</span> <span word="National">National</span> <span word="Academy">Academy</span> <span word="of">of</span> <span word="Sciences">Sciences</span>, <span word="the">the</span> <span word="researchers">researchers</span> <span word="said">said</span> <span word="their">their</span> <span word="find">find</span> <span word="has">has</span> "<span word="far">far</span>-<span word="reaching">reaching</span> <span word="implications">implications</span>"。</p><p>据英国《每日邮报》8月9日报道：通过对坠落地球之前已存在了数十万亿年陨石进行分析，美国宇航局的科学家们发现地球上的生命或许起源于外太空。</p>
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