Free oxygen and ozone disappear from the atmosphere, and all complex life on Earth will die.

游离氧和臭氧从大气中消失，地球上所有复杂的生命都将死亡。

The arrival of free oxygen allowed two major changes to occur on our planet.

游离氧的到来使我们的星球发生了两个重大变化。

It was probably composed of methane, ammonia, water, and hydrogen—no free oxygen was present.

它可能由甲烷、氨、水和氢组成——不存在游离氧。

This is very important, as only free oxygen can enter the cells.

这非常重要，因为只有自由氧才能进入细胞。

By sending the first free oxygen molecules into our atmosphere, and they did all this as single-celled life forms.

通过将第一个自由氧分子送入我们的大气层，它们以单细胞生命形式完成了所有这一切。

Once again, this decrease in hemoglobin affinity for oxygen in our tissues frees up oxygen so it can be used by our cells.

同样，血红蛋白对组织中氧的亲和力的降低释放了氧气，因此可以被我们的细胞利用。