字神帝國英語天地

 今日主題：Bacteria Got an Early Fix on Nitrogen  細菌很早就開始加工氮了
 洪欣老師推薦：托福聽力最好的課外教材：60-Second Science
 康康精選托福會考的主題，堅持每天精聽一定會進步的哦!!
 建議方法：
1. 先聽兩三遍 (不看文稿)
2. 再一句一句聽寫 (每句都要聽寫數遍，直到寫出85%以上的字)
3. 最後check文稿，看哪聽不出來，單字沒背過，還是發音不熟。
4. 堅持天天聽，就能每天進步哦。
 MP3音檔 (按右鍵可下載聽)：喜歡的同學，幫忙推或按讚哦~~
http://online1.tingclass.net/voas…/2015/20150304sa_space.mp3
 只有音檔怎夠，聽不懂地方，不用怕，康康幫你準備好中英文稿了：
 中英文稿：
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.
對地球上大多數生物來說氧氣和水至關重要，那氮呢?它存在於你體內每個基因分子裡，以及你體內所有的蛋白質裡——不誇張地說，沒有它你無法生存。但地球上大多數氮氣都以一種生物體無法利用的惰性大氣氣體形式存在。

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.
雷電能將分氮氣轉化成一種生物可利用的形式。但生物圈中大部分可用氮都是細菌利用一種叫固氮酶的酶將氮氣從空氣中分離出來的。

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.
基於基因遺傳的證據，科學家認為固氮酶首次進化是在約20億年前。在那之前，地球上的生命可能仍僅存在於海洋中，並受關鍵物質的不可取性的限制。

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.
但華盛頓大學的研究人員有證據表明：早在約32億年前固氮酶就存在於細菌中。研究人員的論點是基於澳大利亞古老岩石中重氮同位素的光的比率。該研究發表於《自然》雜誌上。

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.
該項發現表明30多億年前的生物圈比我們目前預測的要復雜得多，而且也許當時生物圈已延伸到了陸地上。固氮酶存在時間的前移也可能意味著，這種酶的發展比當前科學家預測的要更簡單。而這可能會增加天體生物學家遲早在某個遙遠的星球上發現新的強大生物圈存在跡象的機率。