[meteorite-list] cooling rate of irons. drifting to Planetary atmospheres

From: Rob McCafferty <rob_mccafferty_at_meteoritecentral.com>
Date: Tue, 8 Sep 2009 13:45:24 -0700 (PDT)
Message-ID: <428559.72203.qm_at_web55202.mail.re4.yahoo.com>

Predictions have been made of such doomsday scenarios. There's a good one in the book Gaia by Lovelock that begins with some genetic engineering experiment going wrong and it ends up stopping photosynthesis.
The predictions are that eventually the Earth would end up with an atmosphere very similar in proportions to Venus and Mars, both of which are around 97% CO2 with much of the remainder nitrogen and argon.
I forget the surface pressure predicted, I think it was in the region of 90Bar but whether it was more or less I can't remember.
Eventually, the Carbon sealed in rocks would be liberated without photosynthesis to fix it and free oxygen is inherently unstable long term without photosynthesis to replace it.

The irony is that Venus would have started warmer than the Earth and may have been more conducive to the beginnings of life than the earth.
Please, don't anyone suggest panspermia from Venus to Earth. That whole topic seems madness to me.
As the sun warmed up, the increased global temperatures would have driven surface water higher into the atmosphere as the troposphere became saturated where it eventually contributes to global warming rather than cooling by increasing the surface pressure. (This is an oversimplification for brevities sake. I can elucidate to anyone sufficently interested, preferably off list. Not everyone is as anal about these things as I am)
The action of UV light will dissociate H2O at high altitude and the hydrogen will escape to space leaving free oxygen to react with sulphur compounds put into the atmosphere by volcanic eruptions. Sulphucic acid at high altitude is a very potent greenhouse gas (I am told though I will admit I didn't look that up at uni and haven't done since, either) The whole thing runs away.

Whether Venus began a progression to an Earth-like world and then ran away with the greenhouse or whether it has always been like it is is not known.

Still, it provides a stark warning for us on the lil ol earth.
Mars, by contrast has insufficient mass to hold onto a thick atmosphere for more than a few hundred Ma, even at lower initial temperatures. So in 4.56Ga, venus ends up with a 90Bar atmosphere of similar composition to Mars' 0.01Bar atmosphere.
Earth sits nicely in between with its highly modified atmosphere thanks to the actions of plants.

Venus' slow rotation (retrograde, even depending on you frame of reference) seems likely caused by a large impact early in its life, though the loss of a sufficiently large moon would correspond to a big enough loss of spin angular momentum too. The moon would need to be about the mass of Mercury. Whether Mercury was once a moon of Venus or not seems of low probability but if this were the case, the question of where Venus' moon went would need answering.

Considering a large moon seems a vital part in stabilising the spin of a terrestrial planet allowing for complex life to develop (the mixing produced by tides allows for a regular distribution of energy and resources in the shallow water where sunlight can reach near coastlines), I kinda like the Mercury was a moon of Venus idea. It makes complex life far more likely elsewhere. It would mean 2 of 3 terrestrial planets had large moons (mercury no longer being a planet) rather than 1 of 4.

Rob McC




--- On Tue, 9/8/09, Darren Garrison <cynapse at charter.net> wrote:

> From: Darren Garrison <cynapse at charter.net>
> Subject: Re: [meteorite-list] Slow cooling rate of irons in space
> To: "Rob McCafferty" <rob_mccafferty at yahoo.com>
> Date: Tuesday, September 8, 2009, 4:22 AM
> On Mon, 7 Sep 2009 18:37:23 -0700
> (PDT), you wrote:
>
> >Oi!
> >I touched on this. Am I an ivisible voice? Just joking
> with you.
>
> Oh, you?? I have you killfiled.
>
> Actually, I saw your points after I went back and gave the
> thread a more through
> reading after the first skimming.
>
> >Given a rotation of 24(ish) hrs, I wonder what the
> preictions for Venus would be should life such as it is on
> earth be prevelant.
>
> If the atmosphere was the same thickness, I'd think it
> would still be Pretty
> Damn Hot.? I'm no planetologist, but I can't off the
> top of my head think of how
> the slow period of rotation would be able to lead to what
> would otherwise be a
> thin atmosphere.? Of course, we don't know how long
> Venus has had an atmosphere
> like it is currently.? Maybe, if life had taken hold,
> it would have been able to
> evolve some feedback loop keeping the atmosphere from
> getting too thick
> (precipitating out carbon dioxide as calcium carbonate, and
> such.)
>


      
Received on Tue 08 Sep 2009 04:45:24 PM PDT