我了解到这是非常不同的在大氧化事件;不仅仅是相同的元素重新排列。如果所有的自由氧来自水和氢逃到外太空,这不是非常不同。这是大约10 ^ 18升水失去了海洋。地球表面大约是5 x10 ^ 14平方米,占地面积10 ^ 3平方米一升,所以海平面隐约约2米高的地方。世界上有很多的水。人们说的大气有20%的二氧化碳和氧气是从哪里来的。我不相信它,因为有可能不会大幅减少碳当今世界。但它是可能的,随着碳减少,这是沉积在海底,然后俯冲地下深处。它可能仍然存在,等着出去。 Maybe there were other oxidized compounds that got reduced. The obvious candidates are nitrates and sulfates. Today, bacteria mostly reduce nitrates when there is not enough free oxygen. In a series of steps they reduce it all the way to N2, getting energy at each step. Other bacteria convert N2 to ammonia, using considerable energy. Often the ones that do this are photosynthetic. They have N2 and not enough nitrogen compounds to meet their needs, so they make what they need. O2 damages the enzyme. Possibly there used to be a lot more oxidized nitrogen dissolved in the ocean, and the balance shifted, resulting in both increased N2 and increased O2. Maybe there used to be a whole lot more sulfur in the ocean, in the form of sulfates etc. Most of the sulfur got reduced and deposited in the form of elemental sulfur or iron sulfide etc. Then it got subducted away, removing the evidence. What was the pH of the ancient ocean? Convert SO4 to elemental S and 2 O2, and you have removed sulfuric acid. Did the ocean used to be more acid? I don't know, and there were a lot of other buffers anyway. Just as this could happen for sulfur or iron, it could happen with any other good electron acceptor that happened to be dissolved in the ocean. Precipitate it out, and then subduction removes most of the evidence. But only things that had oxygen and then lost it, would contribute to free O2. It was very different, and I can't even assume that the amounts of the various elements present were like today. If it isn't clear what the pH of seawater was back then, I can't even be sure what the maximum amount of dissolved stuff would be. When I tried to guess at the maximum amount of dissolved iron, it turns out it varies with pH, with the amount of other dissolved chemicals, strongly with the amount of organic carbon compounds (because living things in today's ocean can't get enough iron and they scavenge it aggressively), etc. But that's today's ocean, where dissolved iron is quickly oxidized. I expect there's room for a whole lot of uncertainty about all that. But experts can still know some things about it.
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