Based on genetic evidence, scientists have thought that nitrogenase first evolved around 2 billion years ago.

科学家们基于基因遗传证据认为约20亿年前固氮酶就已经完成了第一次进化。

An earlier arrival for nitrogenase also may mean that the enzyme evolves more easily than was previously believed.

固氮酶存在时间的提前也可能揭示酶的发展比科学家早些推测的更为简单。

But researchers at the University of Washington now have evidence for the existence of nitrogenase in bacteria going back some 3.2 billion years.

但华盛顿大学研究人员的证据表明早在约32亿年前固氮酶就存在于细菌中。

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.

但生物圈中的大部分可用氮都是细菌利用一种名为固氮酶的酶氮气从空气中分离出来的。