In learning about mars' past water histroy, which is largely unknown, the topic of earth's own water history came into play. It is my understanding that our ocean became "oxygen rich" only about 500 million years ago, about the time that complex life started to form. Before this period, the oceans were largely devoid of oxygen.

So here's my question. How does a planet have a liquid water ocean seemingly absent of the presence of oxygen? I'm more interested in the chemistry of this answer. To have water, you have 1 hydrogen atom linked with 2 oxygen atoms. Remove the oxygen and you've got hydrogen, which is a gas for the most part. Is the water then just liquid hydrogen? Does something replace the oxygen?? :huh:

After answering this question, how does this effect what we're searching for on/in other planets?

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I am forever striving for increased perfection of my understanding of this world we live in. My quest through life is knowledge and I am but a child on this ubiquitous journey, as are we all. Knowledge, like the universe, is infinite.

The oceans always had oxygen chemically bound to hydrogen in order to consist of water. There's no other way. What is believed to have happened about 500 million years ago was that the amount of free oxygen (dissolved in, not chemically bound to) in the water became sufficiently large to support multicellular life which required more energy than the previous single-cellularers. Plant-like organisms used photosynthesis to enrich the atmosphere and ocean with free oxygen thus wiping out many of the anarchaea.

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For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

Does that mean it had something to do with the rate of "self-ionization of water?" pressumably being much lower than it is today.

I'll quote from my chemistry text.

"At any given time, the number of H30+ and OH- ions present in a sample of pure water is always extremely small. At equilibrium and 24°C, the H3O+ and OH- concentrations are 1.00 X 10^-7M (0.000000100 M)."

This would also create free atoms of H+ and O2- within the solution, correct?

So, if everything here is correct then essentially this rate of self-ionization was even < 1.00 X 10^-7M. Almost to the point of there being no free H+ or O2- atoms present in the water?

As for the plants increasing oxygen both in the water and the atmostphere, assuming my hypothesis is on track, then it was their process of photosynthesis which boosted the rate of self-ionization to the level we see today.

Am I even remotely close here? :huh:

__________________
I am forever striving for increased perfection of my understanding of this world we live in. My quest through life is knowledge and I am but a child on this ubiquitous journey, as are we all. Knowledge, like the universe, is infinite.

I'm not familar with "the self-ionization of water". My guess is that an energy source like ultra violet light or other radiation "tuned" to the binding energy of water molecules, or cell chemistry, is required to produce the ionization you speak of. Are these ions very short lived..say milliseconds per individual?

We should look for the spectral signatures of O, O2, O+, and O2+ in planetary atmospheres when we get good enough. If life is not present, free oxygen won't hang around very long.

__________________
For those inclined to oppose human meddling with the structure of the universe or the composition and configuration of objects and groups of objects within the universe, consider:
Whether there is a limit to the magnitude of a modulation of chaos below which order remains invariant? Or, is order but a fiction invented by perspectives applied over finite, however large, time intervals?

Hmm....good question.

I'd first like to say 2 things. 1) I've just started my studies in chemistry having only completed the general introduction so I have more questions than I do answers about any subject matter. 2) The self-ionization of water is brought about in the chapter on acids, bases and salts and is used to test for the concentration of hydronium ion concentrations in a solution which determines hydrogen:hydroxide ion concentrations in an acid/base solution. In other words, it's a way of determining the pH of a solution with out a peice of litmus paper.

The ion product constant for water is the numerical value 1.00 X 10^-14, obtained by multiplying together the molar concentration of hydronium (H3O+) and hydroxide (OH-) ions present in pure water at 24°C.

This process is useful in determing free agents of hydrogen and hydroxide in solution which, I'm assuming, would also produce free oxygens.

As for the ions' life-span, I'm assuming they're short lived as the self-ionization of water is an equilibrium equation. The factors playing into this such as heat, and as you have mentioned, UV light and/or radiation also come into play. I'm sure there are other factors to. All these factors are out of my league though. I'll need about 3-4 more semesters of chemistry, a couple of classes on geology, a few more calsses on physics and a lot more math in order to give accurate attention to the afore mentioned variables and others not yet mentioned. Hopefully some one could just answer it for me though.

Gotta run. Late for biology. This class helps in my understanding of why organisms need oxygen to produce energy.

Good day.

__________________
I am forever striving for increased perfection of my understanding of this world we live in. My quest through life is knowledge and I am but a child on this ubiquitous journey, as are we all. Knowledge, like the universe, is infinite.

Gourdhead had the answer right in his first post. The source of confusion here is the difference between elemental and molecular Oxygen. Water molecules contain one atom of the element oxygen (and some hydrogen <G>). Oxygen molecules contain two. It's molecular Oxygen that didn't exist in the Earth's atmosphere until photosynthetic plants became common. Some scietists think its concentration passed some sort of threshold 560 million years ago (or so) that allowed complex life to evolve using aerobic energy processes.

And it's so reactive, that if every photosynthetic plant died tomorrow, it would all be gone in a few thousand years.

The self ionization of water has nothing to do with this. That's all about acids and bases, which you've already figured out.

I knew that it had to do with acids and bases all along and technically, water is an acid/base solution. This equilibrium equation generates a small concentration of hydronium and hydroxide ions as well. From my understanding free hydrogen atoms are produced in any acid/base solution. Hence, the testing of H+ to OH- ion concentration in solution.

So, a more direct question is this: Does this also produce free oxygen ions in today's water? The fact that water is an acid and a base makes its rate of self-ionization a factor in early geology, no? Especially if it does in fact produce free molecules of oxygen. I understand that this didn't have much/anything to do with the amount of oxygen in water back then but I still think it's a relevant variable.

Needless to say, I don't think we should get to stuck on this subject matter as I'm definately no chemist. Mostly, I'm checking my understanding and trying to rework it if it is incorrect. But quite frankily, I can't wait another year or two before I can answer it myself.

Does the self-ionization of water produce free oxygen at all? I know photosynthesis does and I have the equation for it, but I don't know how one would write the equation for warter's rate of self-ionization to test for free oxygen atoms.

Sorry if these questions seem dumb.

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I am forever striving for increased perfection of my understanding of this world we live in. My quest through life is knowledge and I am but a child on this ubiquitous journey, as are we all. Knowledge, like the universe, is infinite.

Questions aren't dumb. Sometimes answers are, though

When water self-ionizes, it splits into H+ and OH- ions. The chemistry book you quoted showed the H+ ions as H3O+ implying that the H+ ion binds to a water molecule. This may be the case, but I've never seen it put that way before - my chemistry may be 30 years out of date. But either way, the single oxygen atom never gets totally free of the hydrogen when water self ionizes. It's always bound up in an OH- (hydroxyl) ion. So it can't form O2, ionized or otherwise.

Unless I'm all wet.