托福听力包括两篇对话四篇讲座，对话部分比较简单，讲座部分是难点。虽然讲座部分是难点但是并不是无规律可循，每一个讲座都是围绕个话题展开，上次前程百利小编已经为大家翻译过一篇跟托福听力讲座话题息息相关背景知识。今天给大家带来的是固氮酶的进化，希望对大家备考托福听力有所帮助。
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.
氧气和水对于地球上的生命是很重要的，那么氮气呢？它存在于你身体内的每一个DNA的水分子内，也遍布在你的蛋白质内，也就是说你的生命离不开它。但是地球上的氮气是气体中比较惰性的气体，以至于有机体不能利用。
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.
雷击可以把一部分氮气转化为一种与生物相容的形式。但是生物圈绝大多数的可用氮气都是运用一种叫固氮酶的菌把氮从空气中提取出来。
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.
基于遗传的证据，科学家认为固氮酶第一次是从20亿年前进化而来。在那之前，地球上生命都被限制在水里而且主要的物质所限制。
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.
但是华盛顿的研究者现在有新的证据去证明细菌里的固氮酶存在于32亿年前。研究者基于光的比率，辩论说重氮同位素来源于在澳大利亚的古代岩石中。这项研究发表于《自然》的期刊上。
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.
这项研究表明30亿年前的生物圈比以前预计的要复杂的多，可能已经有了殖民地。早期接触的固氮酶意味着酶的进化比想象中要容易。早晚会提高进化的机率，天体生物学家将会在其他遥远的生物圈找到迹象。
以上就是本期前程百利小编为大家翻译的关于氮气的转化需要的固氮酶的进化，希望大家可以好好利用这些背景材料，提高托福听力。最后前程百利祝大家都能取得理想的考试成绩。
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