Chloride oceans --> chlorine gas?

[ajtribick]

This question inspired by one of the novels in Stephen Baxter's Manifold trilogy: would it be feasible for a lifeform to have a metabolic process which involved producing chlorine gas from chloride dissolved in seawater (possibly in some form of photosynthesis), or would the energy requirements/required concentrations of such a reaction be prohibitive.

[Malenfant]

IIRC according to the Worldbuilding book by Ben Bova that I have (a friend is borrowing it so I can't check), it's theoretically possible for a lifeform to extract Cl from salt etc, possibly as a defence mechanism. Bova suggests that plants could extract and excrete Cl2 as a defense mechanism, resulting in an N2/O2 atmosphere with a few tenths of a percent of biologically generated chlorine in it. The biosphere would have to evolve to be adapted to the chlorine, but he points out that O2 is a very reactive gas and our biosphere is adapted to it so it's not impossible a biosphere to adapt to Cl2.

Even a few tenths of a percent of Cl2 in the air would make a world uninhabitable for humans without protection. But a world where Cl2 is a predominant gas is impossible - the gas wouldn't be biologically produced and it'd react with everything faster than it was replenished.

Which book is this from , BTW? I don't remember a chlorine world in the Manifold (Time, Space, Origin, Phase Space) books.

[Scytale]

I think it would be pretty hard because AFAIK it takes a lot of energy to oxydate the Cl- in water to Cl2... this sort of reaction would definitely not be part of the main metabolic cycle of any organism...

[Brendan]

I loved that book. Stephen Gillett wrote it and Ben Bova edited it. Apparently, it's part of a worldbuilding series.

[eburacum45]

I am not entirely sure that such worlds will really occur without some sort of planetary engineering, but here are some which pop up in Orion's Arm;

http://www.orionsarm.com/science/Chlorine_Worlds.html
http://www.orionsarm.com/xenos/Jade_Chime_Singers.html
http://www.orionsarm.com/worlds/Chorus.html

[eburacum45]

The chlorie world occurs in Manifold:Space by Stephen Baxter; Reid Malenfant is taken to a world with chlorine resistant lifeforms (the chlorine was released as a weapon millions of years ago)

[Malenfant]

I am not entirely sure that such worlds will really occur without some sort of planetary engineering, but here are some which pop up in Orion's Arm;

http://www.orionsarm.com/science/Chlorine_Worlds.html
http://www.orionsarm.com/xenos/Jade_Chime_Singers.html
http://www.orionsarm.com/worlds/Chorus.html

That's rather awesome stuff there...

[eburacum45]

It is nice stuff, from an original idea by Anders Sandberg which Stephen Inniss has expanded upon to a remarkable extent.
Another fine contribution to these pages was by John Dollan, who made the atmosphere for these green worlds.

[ajtribick]

Malenfant - thanks for the info, it seems like the Bova book is worth obtaining. So it sounds like an Earthlike world could get at least some chlorine into the atmosphere without having to be some probably impossible world which formed with implausibly large amounts of hydrogen chloride (the "classical" chlorine world).

Would a few tenths of a percent of chlorine cause noticeable tinting of the atmosphere?