Re: world with less air pressure - survivable?

On Nov 25, 2:48 pm, mn_mn <alexwilliamruss...@xxxxxxxxx> wrote:

How could loss of air happen?

See a response lower in the thread. In short, I don't think it could,
in any short-term (less than evolutionary timescale) fashion.

Everest without extra oxygen at 35% normal pressure is not survivable
for long unless you give people bigger lungs.

For what percentage of the population? I tend to agree with you - but
keep in mind at least one person has spent the night on top of
Everest, on purpose, without supplemental oxygen. 23 hours may not be
"indefinitely", but it's sure longer than I (or for that matter most
physiologists I've talked to) would have suspected.

People could wear masks to let them survive even lower pressure
levels, maybe down to 11% when water in body would boil through
the skin.

I'm not convinced of this. First, even below 0.11 Atm, the skin itself
provides a great pressure garment - you don't "explode in a vacuum",
and your bodily fluids don't "boil" (de-gas, heck yeah, but not boil -
your internal pressure is still well above ambient under those
conditions). At 37 deg-C, the vapor pressure of water is 0.07 Atm,
significantly lower (although I may have messed up a little - I'm
using Del Cotter's trick of Van't Hoff's isotherms).

You certainly would need a positive pressure breathing system (while
the skin may handle pressures that low, the lungs wouldn't/shouldn't),
but not a full spacesuit - perhaps just a good tight bodystocking :).

 Large animals and maybe smaller animals would quickly die, being
sluggish from lack of oxygen means they can't graze or forage fast
enough to convert enough grass.

*VERY* few animals are anywhere near this limit (perhaps hummingbirds
and shrews). What's limiting them is the relative scarcity of food,
not the limit of oxygen to burn it with. So you forage slower... so
does everything else. All this is assuming the atmospheric change
takes place on a timescale much shorter than evolution... which again,
I've really got a problem with swallowing.

 Bacteria need air usually, but I think only they
could evolve in matter of few years to survive lower air levels.

If the Earth's atmosphere went away completely, there would be
bacteria (some) that wouldn't even notice. At least not for millions
of years. If the atmospheric pressure dropped very low, but low enough
to maintain liquid water, the bacterial portion of the ecosphere would
thrive just fine.

Would plants survive with less CO2 in a less dense atmosphere,
I hope most could...

Why do you think a lower-density or lower-pressure atmosphere would
have less CO2? Long-term the CO2 level is set by the carbonate-
silicate cycle, and ignoring minor (potentially mass-extinction-
causing) nudges like burning all the fossil fuels everywhere all at
once, will regulate itself very nicely. Yes, you can have levels of
CO2 that are too low for planets (I think for the C4's, it's around 10
ppm, so there's plenty of room to go down, although C3's would die out
first at (IMS) around 100 ppm or so), but I don't think that's a
significant factor here. Likewise, there might be a limit on nitrogen-
fixing (I don't know of one, but it seems possible).

 I think earth has only a small greenhouse effect so less air might not
mean temperatures change much.

Earth's greenhouse effect is about 33 K. so without an atmosphere,
picture where you live roughly 33 deg-C (60 deg-F) colder. Yeah, I
think there's an important effect here :). The thing is the greenhouse
effect is closely tied up with a large number of things - including
composition, but also the atmospheric temperature gradient. To first
order the temperature gradient wouldn't change, but the height of the
ozone layer (and thus the tropopause and stratopause) certainly would,
changing things significantly. A thinner atmosphere would certainly
effect it, likely make the global temperature drop... but it's going
to be tricky to work out in detail.

 Less air also means less conduction and convection to lose
heat to space.

....and conversely more radiation to loose heat to space (conduction
and convection actually don't loose *any* heat to space. Think about
it). Less air means more efficient radiative transfer, period.

Storms with less air are less destructive.

Not really. You seem to be assuming the storms would have the same
airspeeds, which again may or may not be true.

 Would air be drier?

Why would it? The potential amount of water vapor in the air is set by
the temperature - nothing else. Density and pressure don't enter into
it. So if you want to talk about the global moisture, you need to talk
in terms of energy balances (a 2nd-order effect) not pressures.

Overall I would guess we could lose 1/3 of atmosphere without major
changes, 1/2 of atmosphere and biosphere keeps producing some oxygen,
and 8/10 of atmosphere would mean people live in spacesuit and grow
foot in pressurized greenhouses unless they want ocean algae,

I'm guessing you could drop it to 50% and life would handle it just
fine. Mass extinctions certainly, but if you change any of the basic
parameters by anything like this that's likely to happen.

and below 10% the water even in algae and bacteria would boil so only
minor bacteria deep in ocean survive.

....and if you drop the global pressure so low you start evaporating
the oceans, the atmospheric pressure starts to go up (with a higher
percentage of water vapor in the mix). Depending on the surface
temperature, that might end up being rather high.

Or what if people by spacecraft or maybe a stargate drain the oceans,
can ocean-drained planet survive?

Let's see... can a world without water support water-based life? I'm
just guessing here...

--
Brian Davis

.

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