Ecologies of desert planets

[rancke]

Not sure why you would think that. Oxygen breathing animals use up oxygen, they don't produce it. Granted, they wouldn't be producing large amounts of CO₂, but that might be coming from other sources.

I thought that you were talking about a correspondingly small mass of oxygen-producing organisms replenishing just the small amount of oxygen that the small amount of animals used up. But that wouldn't result in any sort of balance as long as the oxygen was at breatable (for humans) levels, because all the oxygen that the animals didn't cycle would combine with other elements and precipitate -- if that's the word I want -- out of the atmosphere.


Hans

 

[Hemdian]

While working on an adventure set on Yori (C560757-A), a question occurred to me: Where does the free oxygen in a desert world's atmosphere come from? Free oxygen implies vegetation to free it and desert worlds imply a paucity of vegetation. Or does it?

Yori IMTU (see Landgrab) is a dying world. It had an ocean rich with life but lost it. Thus oxygen levels are falling at 1% every 10,000 years. They're already quite low, especially up any mountains.

(One day I'll revise this page with the T5 changes to world size, etc.)

 

[rancke]

Yori IMTU (see Landgrab) is a dying world.

I try hard not to read private landgrabs so that I won't get into trouble with copyrights if I write up a world for publication.

It had an ocean rich with life but lost it. Thus oxygen levels are falling at 1% every 10,000 years.

Lost how? Gradually, over millions of years so that the oxygen in the atmosphere would decrease simultaneously, or somehow from one moment to the next (geologically speaking)? In the second case, just how did that happen?

They're already quite low, especially up any mountains.

Yori's atmosphere is "standard", so the oxygen content can't be all that low.

Also, Shaun Hilburn claimed that oxygen would vanish from the air in millenia, not hundreds of thousands of years, if there wasn't any biosphere to keep the oxygen content up (see post #4 of this thread). Is he wrong about that?


Hans

 

[mike wightman]

Atmospheric oxygen at 15% at stp would be perfectly acceptable to humans.

It is possible that the organisms on the desert world include photosynthetic plant analogues to produce the oxygen, but the ecosystem is designed to trap water within the living bio-sphere.

Ever see pictures of mould eating mould?

Providing the water stays locked within the mould/lichin and isn't released to the atmosphere you have your arid conditions.

What is truly scary is a human setting foot on this world will be a plentiful source of critical water and fare game for whatever can extract it...

 

[esampson]

I thought that you were talking about a correspondingly small mass of oxygen-producing organisms replenishing just the small amount of oxygen that the small amount of animals used up. But that wouldn't result in any sort of balance as long as the oxygen was at breatable (for humans) levels, because all the oxygen that the animals didn't cycle would combine with other elements and precipitate -- if that's the word I want -- out of the atmosphere.


Hans

No. I was referring to a relatively small amount of oxygen breathing organisms. I'm sure someone could find out the amount of oxygen producing biomass on Earth as well as the amount of oxygen using biomass. It is doubtful you would have a better ratio than that on your 'desert planet' and most likely it would be worse (due to the fact that organisms would be hoarding water more which means they wouldn't be converting them to oxygen as rapidly). Since the planet also probably has a much smaller total amount of oxygen producing biomass that would mean that the amount of oxygen using biomass would be far, far smaller than an Earth-like planet.

 

[rancke]

No. I was referring to a relatively small amount of oxygen breathing organisms. I'm sure someone could find out the amount of oxygen producing biomass on Earth as well as the amount of oxygen using biomass. It is doubtful you would have a better ratio than that on your 'desert planet' and most likely it would be worse (due to the fact that organisms would be hoarding water more which means they wouldn't be converting them to oxygen as rapidly). Since the planet also probably has a much smaller total amount of oxygen producing biomass that would mean that the amount of oxygen using biomass would be far, far smaller than an Earth-like planet.

So where does the free oxygen come from? The atmosphere is standard. Not thin. Not very thin. That implies a lot of oxygen-producing organisms. That in turn would seem to require lots of water.


Hans

 

[shaunhilburn]

So where does the free oxygen come from? The atmosphere is standard. Not thin. Not very thin. That implies a lot of oxygen-producing organisms. That in turn would seem to require lots of water.
Hans

Yori is a very small world, much to small to retain a substantial atmosphere, let alone generate one. For perspective, consider that it's larger than the moon but smaller than Mars; about the size of Ganymede. Any naturally occurring atmosphere on such a body would be digit 1 - Trace.

The lack of water, weak gravity, and substantial atmosphere mass implies that the standard atmosphere is an artificial and relatively recent creation.

 

[rancke]

Yori is a very small world, much to small to retain a substantial atmosphere, let alone generate one.

Yori's size has been retconned to 5.


Hans

 

[Hemdian]

I try hard not to read private landgrabs so that I won't get into trouble with copyrights if I write up a world for publication.

If you're going to publish a write-up then fair enough. But if you're just looking for a setting for an adventure then you could ask. (I'm always looking for a way to canonise it.) But I do need to rework all the figures for the new world size.

Lost how? Gradually, over millions of years so that the oxygen in the atmosphere would decrease simultaneously, or somehow from one moment to the next (geologically speaking)? In the second case, just how did that happen?

When working on the landgrab I equated atmospheric pressure with escape velocity. Given the world size of 3 (as it was then) this led to the unfortunate conclusion that the density had to be about 2.2 ... which you can't get naturally according to World Builders Handbook. Something radical led to the compression of the planet's core and it being knocked off its orbit, resulting in an eco-disaster: the rapid loss of its oceans followed by a slowly degrading atmosphere.

(I came up with the basic premis while still in high school (back in the 80s) and never came up with a definitive answer as to why. Given the proximity to Grandfather, was it the Ancients?)

The point is, if you can come up with a reason why a world has only recently (geologically speaking) become a desert world then the oxygen might be left over from before.

Yori's atmosphere is "standard", so the oxygen content can't be all that low.

But even as a 'standard' atmosphere I ended up with an oxygen pressure at base level (there is no sea level) equivalent to an altitude of 3.5km on Earth.

Also, Shaun Hilburn claimed that oxygen would vanish from the air in millenia, not hundreds of thousands of years, if there wasn't any biosphere to keep the oxygen content up (see post #4 of this thread). Is he wrong about that?

It's been so long, I can't remember where I got that figure from. It's entirely possible it was just a wild guess. No one's questioned it until now but I suspect Shaun's figure is probably right.

 

[aramis]

So perhaps the oxygen produced by the worms does ultimately stem from water. Sandtrout form a complex carbohydrate in the form of pre-spice, worms strip the oxygen from the carbohydrate to combine the carbon and hydrogen atoms to carbon dioxide to form new carbohydrates, lipids, and proteins.

It still seems like the process wouldn't produce enough oxygen because Arrakis simply didn't have enough water, but then the population density of its oxygen breathing animals could be very, very low (if we assume some of the hidden life forms that occurred in larger amounts such as sandtrout did not breathe oxygen).

The sandworms are canonically anaerobes, as are the Sandtrout.

 

[aramis]

So where does the free oxygen come from? The atmosphere is standard. Not thin. Not very thin. That implies a lot of oxygen-producing organisms. That in turn would seem to require lots of water.


Hans

It actually implies:

• Total Pressure 0.75 to 1.25 Bar
• Partial Pressure O2 between 0.16 and .5 bar (higher tends to increase fire risks to unsafe levels, and is a long term irritant; short term, up to 2 Bar can be tolerated)
• CO2 ≤1000 PPM (above which it's a taint)
• CO ≤ 20 PPM (above which, it's a taint - a potentially lethal one, at that)
• SO2 ≤ 5 PPM (up to 20 PPM it's a minor irritant; up to 100 is tolerable with correct filters)

And a dozen other things.

It could be 2/3 O2 (500/750 mBar) on a water world, or 1/9 O2 (160/1250 mBar) on a dry heavy desert world...

It may be possible that some of it is from a dry form of CO2 cracking.
Some may be from iron oxide modification.
Some may be from cracking SO2 into other chemicals.

 

[shaunhilburn]

Yori's size has been retconned to 5.

Then retcon the hydro digit, too.

Pick something low, like 1 or 2. The world will still be arid and dusty, while having some plausibilty for the standard atmosphere.