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I was reading my chemistry textbook, when in the chapter on 'solutions', i came across a problem, which calculated the amount of oxygen that can be dissolved in 1cc of water at STP. Then they commented, "this amount is just perfect for aquatic and marine life. Had this been lesser, life in the oceans might not exist at all.' This raised the following question in my mind:

1)aquatic species of flora and fauna evolved over time to adapt to this concentration of dissolved oxygen, and their biological processes were also fine tuned based on the environmental conditions.

2)It really was fate that the dissolved quantity was just enough to support marine life, as the textbook said.

Which of the two is the actual scenario? My personal pick happened to be 1), but I have no proof of it. Can someone explain?

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  • $\begingroup$ That is not really chance but referred to as the contingency of evolution. Any other oxygen concentration would - observed now, after a long time of evolution - seem to be just as perfectly matching. $\endgroup$ – AlexDeLarge Nov 17 '16 at 11:06
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Oh my. Do the authors provide any support for this claim? More importantly: what is their affiliation with creationist organizations? Well, back to science.

First, a note about your question. It might seem that you have sketched out two scenarios, but for the biologist, they are equivalent. We know two things: life exists, and life adapts. Yes, the specific circumstances on Earth have made life possible, and subsequently, life has adapted and fine-tuned itself to those circumstances.

Now to answer your question. I really like the visual representation of the Life Timeline on Wikipedia. 4.1 billion years ago, earliest life appeared on Earth. At that time, all oxygen on the Earth's surface was bound in chemicals like CO2, iron oxide, etc. We are unsure whether the earliest life-forms originiated in the ocean, but we know they ended up there one time or another. The absence of athmosphetic and water-dissolved oxygen of course meant those first life-forms were anaerobes (lived without oxygen). In fact, oxygen was extremely poisonous for our teragrandparents. (We are the ~ 10^12th generation of life.)

So, aquatic life has existed without oxygen, and still exists, whether the solvabily of oxygen is 'perfect' or not.

Another fun fact debunking your chemistry authors statement: water oxygen saturation doesn't reach 100% at all times (linked article provides lots of great information about dissolved oxygen and life, by the way). Lots of life-forms requiring oxygen hence live in a world where the solvability of oxygen is even more than perfect. Furthermore, life exists (but doesn't thrive) in low-oxygen conditions (e.g. pubmed:9510533).

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The claim is strange since many bacteria don't use oxygen, and since oxygen is indeed a by-product of early life (thus not using it. Oppositely, oxygen is indeed a poison for cells that they had hard time to protect against, then get able to have some use).

Moreover the amount of dissolved oxygen varies with places, depth, temperature, and along geological times.

So, answer 1.

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  • $\begingroup$ It was quite clearly answering 1. I made it explicit :-) . $\endgroup$ – Fabrice NEYRET Nov 17 '16 at 17:26

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