Board Thread:Questions and Answers/@comment-90.244.94.220-20141004224535/@comment-4621372-20141014014820

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No. Free Oxygen is ridiculous. It would stay "Free" for about 10 seconds, and then it would bond indiscriminately. Shit, that happens with O2, as well, just much more slowly, which is why if all the photosynthesizing organisms disappeared, the earth would run out of oxygen in a few years.

Not that that matters, cuz the Free Oxygen would bleach the shit out of the earth LOOONG before then.

Part from that, not much difference.

Here's the issue; if you change anything in such a way that it actually makes a difference, said difference is going to be making life on Earth impossible.

- Nothing can breathe chlorine. No "aliens" can do that, cuz the issue isn't with processing chlorine, it's that the chlorine will bleach your lungs, and nothing survives that.

- Save for flourine, there's nothing more deadly that Free Oxygen- literally nothing will survive contact unscathed with it, organic, inorganic, whatever.

There are, however, a few changes.

A lack of carbon in the early Earth could lead to sillicate based life, but that's going to be unaffected by the atmo.

A surfeit of arsenic, however, could get you somewhere. The reason arsenic is so deadly is because it replaces phosphorus, which your cells use. Theoretically life could use arsenic.

Just as a side note, while a similar thing happens with Carbon Monoxide, life cannot be sustained with CO. See, your hemoglobin would much rather bond with CO than O2, so when you breathe more than a little CO, your blood bonds with that, but since SOMETHING is bonding with your blood, you won't even notice. First you'll feel kinda happy, then your lips will turn kinda red, and then you'll fall asleep and die. However, because O2 is used for Combustion- which CO cannot be used for- a replacement just results in a painless death. Arsenic, on the other hand, can, with a few tweaks to the molecules, fulfill the same role as Phosphorus.

There are a few theoretical amino-acids that aren't used in life as we know it. An abundance of a few of those base molecules could form amines that would also exist in this life.