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美宇航局发现火星细菌 成生命新证据
作者：maisie  文章来源：本站原创  点击数  更新时间：2009-12-8 8:40:14  文章录入：maisie  责任编辑：maisie

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美宇航局发现火星细菌 成生命新证据[文章来自:考试与评价 http://www.trgroup.com.cn/te/ 'j 410nhP+43R^S_v]
Nasa: compelling evidence of life on Mars[文章版权 禁止转载:考试与评价 http://www.trgroup.com.cn/te/ H?3m FK-/M=gw/ D(c5FroG]

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Nasa has found what it calls “strong evidence” that life once existed on Mars after re-examining a meteorite.

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A research team at Johnson Space Centre in Houston has been re-examining a meteorite that hit Antarctica 13,000 years ago, and found the most compelling evidence yet that the planet once harboured bacterial life.

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The team says that microscopic crystals found in the rock are almost certainly fossilised bacteria that have many characteristics in common with bacteria found on Earth.

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“The evidence supporting the possibility of past life on Mars has been slowly building up during the past decade,” said David McKay, Nasa chief scientist for exploration and astrobiology.

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“This evidence includes signs of past surface water including remains of rivers, lakes and possibly oceans and signs of current water near or at the surface.”

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The debate centres on magnetite crystals found in the meteorite. A study carried out in 1996 suggested that they were biogenic - produced by living organisms.

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Critics, however, suggested that the magnetite was formed by a chemical process called thermal decomposition.

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The new paper uses more advanced instruments to refute the critics’ theory, arguing that ancient life remains the most plausible explanation.

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“We believe that the biogenic hypothesis is stronger now than when we first proposed it 13 years ago,” said Everett Gibson, a Nasa scientist.

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近日，美国宇航局发现火星曾存在生物体的“有力证据”，这一结论是在该机构对一枚陨星进行重新检测后得出的。

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位于休斯敦约翰逊宇航中心的一个研究小组对1.3万年前撞击南极洲的一枚陨星进行了再次分析，发现了迄今为止可证明火星曾存在细菌生命体的最有说服力的证据。

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研究小组称，他们在岩石上发现的微小晶体几乎可以断定是石化细菌，这些细菌和地球上的细菌有很多共同特征。

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美国宇航局探测和天体生物学首席科学家戴维•麦凯说：“在过去十年间，火星可能曾存在生命体的证据逐渐增多。”

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“这其中包括火星曾存在地表水的证据，如河流、湖泊、甚至可能大海残留的痕迹；以及地表或地表附近存在水流的证据。”

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有关火星存在生命体的争论主要集中在这块陨星中所发现的磁性晶体上。1996年开展的一项研究认为，这些晶体是有机生物体的生命遗迹。

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但批评人士认为，这枚陨星是在热分解的化学过程中形成的。

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为反驳批评人士的说法，新的研究报告使用更先进的仪器进行检测，并称远古生命遗迹是最合理的解释。

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美国宇航局科学家艾弗瑞特•吉布森说：“我们相信，现今有关火星存在生物体的假设比13年前刚提出时更有说服力了。”

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