科学美国人60秒 细菌很早就发现了氮

Oxygen and water are crucial to most life on Earth, but what about nitrogen? It’s in every molecule¹ of DNA² in your body, and in all your proteins—you literally³ can’t live without it. But most of Earth’s nitrogen exists as an inert⁴ atmospheric⁵ gas that organisms can’t use.

对地球上大多数生物来说氧气和水至关重要，那氮呢?它存在于你体内每个基因分子里，以及你体内所有的蛋白质里——不夸张地说，没有它你无法生存。但地球上大多数氮气都以一种生物体无法利用的惰性大气气体形式存在。

Lightning strikes can convert some nitrogen into a bioavailable form. But most of the biosphere⁶’s usable nitrogen is the result of bacteria employing an enzyme⁷ called nitrogenase to pull nitrogen out of the air.

雷电能将部分氮气转化成一种生物可利用的形式。但生物圈中大部分可用氮都是细菌利用一种叫固氮酶的酶将氮气从空气中分离出来的。

Based on genetic⁸ evidence, scientists have thought that nitrogenase first evolved around 2 billion years ago. Before that, life on Earth might have been confined to the oceans and been limited by the crucial substance’s inaccessibility⁹.

基于基因遗传的证据，科学家认为固氮酶首次进化是在约20亿年前。在那之前，地球上的生命可能仍仅存在于海洋中，并受关键物质的不可取性的限制。

But researchers at the University of Washington now have evidence for the existence of nitrogenase in bacteria going back some 3.2 billion years. The researchers base their argument on the ratios of light to heavy nitrogen isotopes¹⁰ in ancient rocks from Australia. The study is in the journal Nature.

但华盛顿大学的研究人员有证据表明：早在约32亿年前固氮酶就存在于细菌中。研究人员的论点是基于澳大利亚古老岩石中重氮同位素的光的比率。该研究发表于《自然》杂志上。

The finding indicates that the biosphere more than three billion years ago was much more complex than previously¹¹ appreciated, and perhaps had already colonized¹² land. An earlier arrival for nitrogenase also may mean that the enzyme evolves more easily than was previously believed. Which could increase the odds¹³ that, sooner or later, astrobiologists will find signs of another robust¹⁴ biosphere on some world far away.

该项发现表明30多亿年前的生物圈比我们目前预测的要复杂得多，而且也许当时生物圈已延伸到了陆地上。固氮酶存在时间的前移也可能意味着，这种酶的发展比当前科学家预测的要更简单。而这可能会增加天体生物学家迟早在某个遥远的星球上发现新的强大生物圈存在迹象的几率。

1 molecule   

n.分子，克分子

参考例句：

• A molecule of water is made up of two atoms of hygrogen and one atom of oxygen.一个水分子是由P妈̬f婘̬ 妈̬成的。
• This gives us the structural formula of the molecule.这种方式给出了分子的结构式。

2 DNA   

(缩)deoxyribonucleic acid 脱氧核糖核酸

参考例句：

• DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
• Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。

3 literally   

adv.照字面意义，逐字地；确实

参考例句：

• He translated the passage literally.他逐字逐句地翻译这段文字。
• Sometimes she would not sit down till she was literally faint.有时候，她不走到真正要昏厥了，决不肯坐下来。

4 inert   

adj.无活动能力的，惰性的；迟钝的

参考例句：

• Inert gas studies are providing valuable information about other planets,too.对惰性气体的研究，也提供了有关其它行星的有价值的资料。
• Elemental nitrogen is a very unreactive and inert material.元素氮是一个十分不活跃的惰性物质。

5 atmospheric   

adj.大气的，空气的；大气层的；大气所引起的

参考例句：

• Sea surface temperatures and atmospheric circulation are strongly coupled.海洋表面温度与大气环流是密切相关的。
• Clouds return radiant energy to the surface primarily via the atmospheric window.云主要通过大气窗区向地表辐射能量。

6 biosphere   

n.生命层，生物圈

参考例句：

• The entire biosphere was becoming more transparent.整个生物圈越来越透明。
• The impact of modern technology on the biosphere is evident worldwide.现代技术对生物圈的影响在全世界是明显的。

7 enzyme   

n.酵素，酶

参考例句：

• Above a certain temperature,the enzyme molecule will become unfolded.超过一定温度，酶分子将会展开。
• An enzyme that dissolves the fibrin of blood clots.能溶解血凝块中的纤维的酶。

8 genetic   

adj.遗传的，遗传学的

参考例句：

• It's very difficult to treat genetic diseases.遗传性疾病治疗起来很困难。
• Each daughter cell can receive a full complement of the genetic information.每个子细胞可以收到遗传信息的一个完全补偿物。

9 inaccessibility   

n. 难接近, 难达到, 难达成

参考例句：

• Her tone and her look still enveloped her in a soft inaccessibility. 她的语调和神态依旧把她禁锢在一种不可接近的状态中。

10 isotopes   

n.同位素；同位素( isotope的名词复数 )

参考例句：

• the many isotopes of carbon 碳的诸多同位素
• Tritium is one of the mildest radioactive isotopes. 氚是最和缓的放射性同位素之一。 来自《简明英汉词典》

11 previously   

adv.以前，先前（地）

参考例句：

• The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
• Let me digress for a moment and explain what had happened previously.让我岔开一会儿，解释原先发生了什么。

12 colonized   

开拓殖民地，移民于殖民地( colonize的过去式和过去分词 )

参考例句：

• The area was colonized by the Vikings. 这一地区曾沦为维京人的殖民地。
• The British and French colonized the Americas. 英国人和法国人共同在美洲建立殖民地。

13 odds   

n.让步，机率，可能性，比率；胜败优劣之别

参考例句：

• The odds are 5 to 1 that she will win.她获胜的机会是五比一。
• Do you know the odds of winning the lottery once?你知道赢得一次彩票的几率多大吗？

14 robust   

adj.强壮的，强健的，粗野的，需要体力的，浓的

参考例句：

• She is too tall and robust.她个子太高，身体太壮。
• China wants to keep growth robust to reduce poverty and avoid job losses,AP commented.美联社评论道，中国希望保持经济强势增长，以减少贫困和失业状况。