科学美国人60秒 细菌很早就发现了氮（在线收听）

Oxygen and water are crucial to most life on Earth, but what about nitrogen? It’s in every molecule of DNA in your body, and in all your proteins—you literally can’t live without it. But most of Earth’s nitrogen exists as an inert atmospheric 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 biosphere’s usable nitrogen is the result of bacteria employing an enzyme 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 genetic 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 inaccessibility.

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 isotopes 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 previously appreciated, and perhaps had already colonized land. An earlier arrival for nitrogenase also may mean that the enzyme evolves more easily than was previously believed. Which could increase the odds that, sooner or later, astrobiologists will find signs of another robust 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。