Yet Another Brain Fart -- err, plot bunny

[Valles]

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Chlorine is greenish yellow under the light of a yellow sun. Under the light of a hotter, bluer, sun, it will look different. Of course, the aliens might not be breathing chlorine gas. With no free oxygen, you could have seas of carbon tetrachloride, used in the same way as chlorine gas would be.

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So, in short, their primary is probably an F-type star? No problem, there are plenty around.
I've had a thought - chlorine is scarcer than oxygen, but if its interactions require more energy, might they not also yield more, ie, support the same size of organism on a lower partial pressure?

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As a side thought maybe hyper space shouldnt have thawed so long ago say the crystal breaks up if exposed to organized energy waves (like radio signals) for a long enough time in a large enough volume (say a few decades).

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This fails to account for things like Pulsars and such... Also, the fact that interstellar travel was becoming impossible in our area was, in my mind, why the Precursors had moved on to other projects.
I'm going to bow out of the 'speciation argument' for the time being, but if it keeps being a problem, I actually know an expert to ask... I'd rather not bother her, though.
Ja, -n

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