地球生命可能起源于外太空

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作者：Michael P. Callahan 来源：PNAS 发布时间：2011-8-16 ( H  z$ [6 C9 j. l6 |# z2 X1 B0 p" l

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; s5 ?8 a# ?& O 这颗行星上的生命可能起源于一次宇宙变故
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* Z3 M6 w: o* G& n北京时间8月10日消息，据国外媒体报道，美国宇航局的科学家通过对来自外太空的陨石进行分析，认为地球生命可能起源于外太空。这些陨石在坠落到地球上以前，已经形成数亿年。
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科学家发现，这些富含碳的碎片包含类似于DNA的一种重要组成成分的化合物。检测结果显示，这些化学物质的出现不能通过地球污染物的说法加以解释，这表明DNA可能起源于外太空。美国科学家、优秀的美国宇航局研究人员通过分析12块陨石的化学成分，获得上述发现。该研究成果发表在美国《国家科学院院刊》（PNAS）上，他们在论文里说，他们的发现具有“深远意义”。+ @; Y0 a0 P' S2 }* ^' Z5 I
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该研究负责人、马里兰州美国宇航局戈达德太空飞行中心的迈克尔-加拉汉博士说：“地球形成初期的陨石和彗星撞击，确实为地球带来一些至关重要的生命组成成分。”以前的研究发现，陨石蕴含着三种生命重要成分中的另外两种。它们分别是氨基酸（串在一起形成蛋白质的“珠子”）和促使细胞产生隔膜“屏障”的化学物质。DNA里的化学物质是第三种。(来源：新浪科技 孝文)  
5 X7 D1 \* d: }6 ZCarbonaceous meteorites contain a wide range of extraterrestrial nucleobases0 G6 T+ Y! x" t5 s' p

2 W7 ]0 I0 S1 K: l  e# K5 kMichael P. Callahana,1, Karen E. Smithb, H. James Cleaves IIc, Josef Ruzickad, Jennifer C. Sterna, Daniel P. Glavina, Christopher H. Houseb, and Jason P. Dworkina 4 }1 @* Q. F  f; E
+ Author Affiliations
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. v( d" [2 @# ~& x. J/ caNational Aeronautics and Space Administration Goddard Space Flight Center and The Goddard Center for Astrobiology, Greenbelt, MD 20771;
& Y, |6 q% ~6 `' C2 _bDepartment of Geosciences and Penn State Astrobiology Research Center, Pennsylvania State University, 220 Deike Building, University Park, PA 16802; - o" W8 f  W( Q/ W" }3 Q% Z
cGeophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015; and 6 r" t" T3 e/ X( b: j8 V
dScientific Instruments Division, Thermo Fisher Scientific, Somerset, NJ 08873
8 B- |/ L* P  v4 F+ jEdited by Mark H. Thiemens, University of California San Diego, La Jolla, CA, and approved July 12, 2011 (received for review April 25, 2011)
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; o& v6 r) s+ B6 \7 h4 eAbstract1 r2 P8 _* ~; H3 F  P6 _, i
All terrestrial organisms depend on nucleic acids (RNA and DNA), which use pyrimidine and purine nucleobases to encode genetic information. Carbon-rich meteorites may have been important sources of organic compounds required for the emergence of life on the early Earth; however, the origin and formation of nucleobases in meteorites has been debated for over 50 y. So far, the few nucleobases reported in meteorites are biologically common and lacked the structural diversity typical of other indigenous meteoritic organics. Here, we investigated the abundance and distribution of nucleobases and nucleobase analogs in formic acid extracts of 12 different meteorites by liquid chromatography–mass spectrometry. The Murchison and Lonewolf Nunataks 94102 meteorites contained a diverse suite of nucleobases, which included three unusual and terrestrially rare nucleobase analogs: purine, 2,6-diaminopurine, and 6,8-diaminopurine. In a parallel experiment, we found an identical suite of nucleobases and nucleobase analogs generated in reactions of ammonium cyanide. Additionally, these nucleobase analogs were not detected above our parts-per-billion detection limits in any of the procedural blanks, control samples, a terrestrial soil sample, and an Antarctic ice sample. Our results demonstrate that the purines detected in meteorites are consistent with products of ammonium cyanide chemistry, which provides a plausible mechanism for their synthesis in the asteroid parent bodies, and strongly supports an extraterrestrial origin. The discovery of new nucleobase analogs in meteorites also expands the prebiotic molecular inventory available for constructing the first genetic molecules. / Q0 a! P' E) U! h

* H3 m& X5 L5 O" ?http://www.pnas.org/content/earl ... 0-a7eb-00197a319cef