Queen of Swords

Can anyone think of an even halfway scientific way for oxygen-breathing animals to live in sealed underground tunnels in the complete absence of light, i.e. no photosynthesis? Let's also assume that there is no ventilation to bring in oxygen from the surface or anywhere else. However, there are plenty of decomposing materials and even water. Is there any way to produce oxygen besides photosynthesis?

If not, can you imagine a necessary chemical reaction and suggest an organism that could carry it out, in the absence of plants or algae?

Coragyps

This is for an SF story, nu? Is intelligence involved, so you can use electricity from geothermal or fermentative sources? Or does the oxygen need to be there "naturally?"

PaulT

There have been examples discovered of colonies of underground animals exactly like you describe, living in sealed caverns underground without light. In place of photosynthetic organisms, the base of the food chain in these caverns is chemosynthetic, like the bacteria which live at the steam vents on the ocean floor. There are several specific chemistries that have been discovered at work there -- just figure that in order for your 'oxidizing'-type animals to eat them, the bacteria have to be performing some sort of catalyzed reduction reaction: Fe++ to Fe+++, or NH3 to NH4+. Then the animals feed on the bacteria, combining their reduced ions with oxygen to release energy. In the ocean, or in a dark cave underground on Earth, this works because free oxygen is already available in the water, dissolved from the atmosphere -- so as long as there's some water leakage into the cave, a few animals can survive even without oxygen being produced in situ.

I believe oxygen might be produced in ammonia reduction reactions also -- NH3 to NH4+ removing the hydrogen from a water molecule and leaving free oxygen. Clearly this is endothermic, but perhaps with geothermal heat, or driven by the kind of chemosynthetic process I described above, it wouldn't be impossible to create oxygen in a lightless environment.

Undercurrent

It seems to me that the specific chemical reaction is not as important as the energy source driving the reaction. Without some energy input (I'm thinking either geothermal or nuclear, like the Oklo reactor, or chemical) all of the creationist complaints about the second law of thermodynamics suddenly become valid criticisms.

m.

Coragyps

Strictly "chemically" I can offer
lead dioxide + heat = lead monoxide + oxygen
or
sodium peroxide + carbon dioxide = sodium carbonate + oxygen.
The latter is nice, both because it recycles your waste CO2 and because it doesn't have lead poisoning issues - just chemical burns from the sodium peroxide. I think this is actually used on manned space probes.
Now as to how either of these chemicals got down by the tunnels in the first place.... but hell, if folks can't suspend their disbelief, they need to stick to reading the Bible, right?

Edited to add: I once saw a footnote in some advanced chemistry text citing Agatha Christie - maybe Pale Rider - as a reference to the toxicity of thallium compounds. So science and art really can feed off each other.

[ June 03, 2002: Message edited by: Coragyps ]</p>

Queen of Swords

This is actually for a fantasy novel. Call me nitpicky, but even if make-believe animals are sealed into vast catacombs, I want to know how they're going to survive.

SanDiegoAtheist

Actually, if I remember correctly, a similar pathway to reaction #2 is actually used by some bacteria which exist around oceanic vents. They use H2S & CO2 from the vents and give off O2.

Just have some nice hot mineral pools in your caverns and have a healthy supply of these critters around

Cheers,

The San Diego Atheist

[ June 03, 2002: Message edited by: SanDiegoAtheist ]</p>

Undercurrent

My understanding was that these bacteria give off S2 rather than O2. But I could have just been not paying attention.

If you(QoS)'re making this thing up whole cloth, maybe a large coral reef-like organism colony that, instead of using calcium carbonate for its skeletal structure, uses iron or aluminum. It would (with a suitable energy source) extract oxides of these from the surrounding rocks and give off oxygen as the polyps reduce the oxides to their elemental forms.

m.

ohwilleke

If its the oxygen supply your worried about, finding a source of oxygen is not really the problem. Almost all common rocks (silica that makes up sand, granite, limestone, etc.)have a substantial component of oxygen in them. Getting oxygen out of water is also not particularly difficult.

Also, on Earth and any non-dead planet, natural uranium deposits provide a fairly constant level of heat in the interior. Add to that tidal gravitational forces and heat on the surface seeping down, and energy isn't a real problem.

Probably the biggest problem is not generating oxygen per se (this is a closed system, so once you have enough it isn't going anywhere), it is cleaning the CO2 produced by respiration from the atmosphere. Photosynthesis doesn't just fix solar energy and produce breathable oxygen. It also takes CO2 out of the atmosphere.

Here's an interesting idea, although it doesn't solve the too much CO2 problem (chemistry was not my strong point). Air on earth is composed primarily of nitrogren (N2), oxygen (O2), and carbon dioxide (CO2). Both N2 and CO2 are odorless, colorless gasses which are basically harmless in and of themselves. (Deep sea divers, for example, do just fine, indeed better, without any N2 in their oxygen tanks). Too much CO2 is bad mostly because it squeezes out O2 and creates a greenhouse effect. But, in an underground environment, where the nitrogen cycle is unnecessary to feritilize photosynthetic plants, one could easily imagine humans and other oxygen breathers doing perfectly well in air which has very little N2 and lots of CO2, instead of the other way around. And, if most of the air was CO2, instead of N2, one would imagine that a less efficient process than photosynthesis could suffice to convert CO2 to O2.

Back to the nitrogen cycle. Decomposition of dead animal and vegitable matter is important on Earth in large part because it sustains the nitrogen cycle, which feeds photosynthetic plants. It is not obvious that in an underground non-photosynthetic world, this nitrogen cycle would be as important, hence decay might not be as important anyway.

And, while getting energy input isn't all that important a problem (geothermal is plenty sufficient), there is the problem of how to fix energy to make it useful for animals. Plants or animals that fix heat energy would seem necessary.

Note also that while photosynthesis is important in the oxygen-carbon dioxide cycle, the nitrogren cycle and energy fixing on Earth, that there is no logical reason why all three would have to have the same source in an underground world. There could be one process that keeps the oxygen-carbon dioxide mix balanced, and another that fixes energy. One could even imagine a world in which there was no microlevel decay of biological matter, this being done more episodically through digestion by macroscale animals.

One would also imagine that some version of cold-blooded life would make a great deal of sense in an underground environment. Being cold blooded on the surface can be a disadvantage because you have to slow down when it gets cold. But, in a more or less constant temperature environment, there is no compelling reason not to be cold blooded. Since a cold blooded creature gets much of its body heat directly from the environment, rather than generating it chemically, as warm blooded creatures do, they would seem to be well suited to an underground environment where fixing heat energy is a problem.

lpetrich

What one really needs is a continuous supply of materials in chemical disequilibrium, and sealed catacombs will not have such supplies.

However, if they are not completely sealed, then it's another story. But even then, the biological productivity will be limited by the supply rate of in-disequilibrium materials.

The simplest way for oxygen to get in is to leak from outside. Foodstuffs are a more difficult problem, but there are ways to get in, such as being washed in from outside or dropping in (dead bats, etc.).

However, a cave with a hot spring can provide an oceanic-hot-spring-like ecology; various oxidizable gases seep in, like hydrogen and methane and hydrogen sulfide. These then are oxidized by certain bacteria, which then become eaten by small crustaceans and the like, which then become food for fish and the like, ...

But even so, there is not likely to be much to eat in a cave.