I want to have an intelligent life-form on a planet, but I want this life form to be technologically limited because of the lack of discovery of fire.
What changes would have to occur in the atmosphere for this to occur, and what effect would this atmosphere have on any human life or human technology on the planet, eg. using fuel based thrusters in this atmosphere?
How about we keep the ability to start fires artificially, but make enough changes so that fires do not start naturally?
There are two main causes that lead to natural fires:
We need to change the atmosphere such that the direct heat from the sun is greatly reduced, and also to reduce the creation of rapid vertical movements of air masses. In the realms of science fiction, we need very fine metallic dust mineral fibers dotted with small pirite crystals floating in the air. This amazing fiber is produced without the pirite crystals by volcanoes and can naturally float in the air. In our story it is the result of some very nasty ancient volcanic explosions. The difference from the naturally occurring Pele's hair that I found on the internet, is that we are going to sparkle it with iron crystals. Note that Pele's hair is part of the mineral wools that are considered to be fire-retardants.
The fibers are glassy and sprinkled with highly reflective pirite crystals, thus it will be reflective, increasing the overall albedo of the planet, and it will be most dense in the tropics. The reason for the increased density is that the hotter air, being more rarefied, will cause a local accumulation of the fibers, hence increasing the local concentration, and as a by-product, the local albedo.
The minimum local density of the fibers will also be such that there is never enough difference of electrostatic potential to generate any meaningful spark. Any difference in electrostatic potential will be discharged between the pirite crystals harbored on the mineral fibers. Think of it like living inside a block of metal. All the charges will be distributed in the upper layers of the atmosphere, and ancient hominids will enjoy lightnings only at the boundary between the thermosphere and the exosphere. Considering that Pele's hair has a ridiculously high ignition point, good luck igniting anything up there.
Finally, although it is not part of the atmosphere, I would remove all those piezoelectric rocks, and place all volcanoes that are active during the evolution of mankind well under the sea. Plenty of free-air active volcanoes up to the Mesozoic, fill the atmosphere with the pirite-dotted mineral wool, and then bury all of the under hundreds of meters of water. There too, good luck seeing lava igniting anything.
Finally, to avoid even will-o-the-wisps, we need to add some methane-digesting bacteria to the environment. These otherwise harmless bacteria, which live attached to the floating mineral wool, use the pirite crystals as catalytic agent to degrade methane into CO2 and water, without burning it. This will also take care of local methane spillage.
Humans will need thicker nose hair to filter the metallic dust mineral wool fibers and prevent some nasty lung carcinomas. I think that natural selection will eventually favor homo-mustachios over homo-sapiens.
The beauty of all this is that we are still in a O2-rich environment. Happy breathing.
PS a big thanks to rek's, John's, and celtschk's constructive comments.
High oxygen environment.
Low oxygen environment might work. But how dull.
I propose a high oxygen environment. This scheme has been bandied about here before. Advanced civilization in high oxygen atmosphere. Your environment would be 35% O2 (like Earth in the Carboniferous) or higher. You could have constant high humidity or rains to decrease wildfires. Artificial fires would burn explosively and near-uncontrollably. Domesticating fire would be like domesticating african elephants, or cape buffalo - not technically impossible, but extremely dangerous.
Plus: giant dragonflies!
There are three sides to the fire triangle, fire, fuel, and heat Did you mean oxygen, fuel and heat? Recursive fire triangles sound really dangerous!
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Add something to the atmosphere that suppresses fire.
If there was 5-7% Halon over the whole planet fires could not exist. Respiration would still work, though there are toxicity concerns.
There are several fire suppressing gasses, though an atmosphere's worth of any of them existing naturally is doubtful, and it decomposes into terribly toxic products and destroys ozone. So this may just move the handwaving back one step.
I'll take the boring option.
Boring, you say? What about developing live from the anaerobic organisms?
It'd be a lot of work, as they are some bacteria and such. But if you give aerobes no chance, your whole multi-cell and sapient life might be anaerobic. You'd need to fix prehistoric cyanobacteria for this, and then let the life cook and refine itself for few milliards of years.
If the planet is covered in one single ocean, no one would be able to start a fire until they discovered thermite or invented phosphorus torches.
You may have islands here and there, as long as they have nothing flammable on them.
Of course, the dominant intelligent lifeforms would probably be breast-singing, and possibly ram-ventilating mermaids/tritons.
As for the effect that would have on thrusters, those would be capable of operating just fine. The atmosphere over the ocean could be just like ours.
The only way to do this is to exclude oxygen from the atmosphere.Anywhere that life depends on oxygen and creates an oxygen atmosphere will be fire prone, because of that same reactivity of oxygen. The only solution is to have life with a non-oxygen atmosphere.
Oxygen is probably impossible to find in an atmosphere in any planet without life, because it is too reactive. It will immediately bind with carbon, hydrogen, nitrogen, iron, or any of the other common elements in the universe (except helium, obviously). Over geological time, you simply won't find pure oxygen at human-like temperatures and pressures.
The choices are nearly endless, but here is a Wikipedia link about hypothetical bio-chemistries. You can pick one of these that allows metabolic pathways to operate without free oxygen.
Mobile life needs a chemical that reacts easily with most other chemicals to extract energy and nutritive byproducts. This chemical needs to be plentiful for life to thrive. So here on Earth we have oxygen. These are known as oxidizing agents, and there are many, but only a handful are gaseous.
The key takeaway here is that fire also requires an oxidizing agent, it needs to be plentiful - and it will occur where life is found because it's required for that life.
So wherever you have mobile life, that life will necessarily have all the ingredients to make fire, and fires will occasionally occur naturally in the same way that life occurred naturally.
We do have life that is based on non-oxidation reactions, though. Plants and non-mobile life forms use a different source of energy for their reactive processes - sunlight.
There's not enough sunlight, however, to form intelligent life due to the exceptional energy requirements of intelligence. If you irradiate a planet with enough energy to supply such demands you prevent the formation of the compounds needed to form even plants. Perhaps you could come up with a plant that lives mostly in shelter (underground) and exposes only its brain to a scorched earth scenario with enough radiated energy to power the intelligence, but I think that unlikely, and at that point what use is fire - or the lack of it - since the organism itself isn't free to move, or if it can does so only at a glacial pace.
The result is that the only possible way to form such a situation is by changing some other characteristic that allows fire - for instance having an aquatic society where oxygen exists, but other factors prevent fires.
Easy: High pressure, "low" oxygen world. For a really extreme example of this look at very deep scuba diving--there are realms where the proper breathing mixture is hydrogen/oxygen. Sounds like you have a big bomb strapped to your back but you don't--it won't burn because there's not enough oxygen.
The thing is, fire depends on the percentages. A low enough percentage of oxygen means the other gases absorb the heat, fire doesn't get hot enough to burn. However, our metabolic processes depend on the absolute pressure of the gases. At Earth's surface we breathe 3 psi of oxygen with about 12 psi of nitrogen mixed in. In space we used to use 3 psi of oxygen with nothing mixed in--our body does fine on this (but you need to be careful of the bends!) but we no longer use it because of the fire danger.
So long as we have that 3 psi of oxygen (and no more than 12 psi for extended use) and no more than about .2% of carbon dioxide the other gases are irrelevant until they reach toxic levels. (Which is actually the depth limits for scuba diving--it's not the pressure that stops us, it's the fact that we reach a point where there's nothing that can be used as a filler.)
Because if it weren't humans, things would immediately become very simple. Say, you have a planet, where oxygen exists in liquid form only. Then oxygen breating life form can drink it and breathe this way. If you have no other oxidizers lying around, you're set - starting a fire would require significant efforts, thrusters will work almost as usual using a liquid fuel mix.
Or in other words, an atmosphere that is already so fuel-rich combustion cannot sustain itself. Could aerobic life operate here? Sure -- the process of cellular respiration is essentially step-wise and controlled enough that all the methane can simply be kept aside where it doesn't bother anything. Uncontrolled fires would simply fizzle out before they got beyond the "hot ember" stage, though. The water cycle would still work as intended, although the nitrogen cycle would need to be altered with a non-nitrogenous atmosphere (most nitrogen would be either ammonium or nitrate/nitrite in soils, with a small amount as dinitrogen).
Taming fire on this planet would be an...interesting exercise. Instead of having to pipe fuels about like we do on Earth, the locals would be distributing and storing oxidizers, in order to get to a combustible mixture from what's already in the air. Perhaps their cars would run on dinitrogen tetroxide and their furnaces on nitrous oxide?
No, it would not be possible via changing the air composition only.
Humans consume oxygen in the same way that fire consumes it - the process oxidizes material and releases energy. And it would be very difficult to allow breathing, but not burning. Humans can tolerate oxygen concentrations down to 16% (compared to normal 21%), while most flammable materials can burn at lower oxygen concentrations.
If all the "plant life" was non-combustible, and there were no standing pools of hydrocarbons, and no piles of combustible metals, it would be rather unlikely that an "intelligent" life form would discover fire.
The problem with the main assumption is that the "Aliens" even need to evolve in an oxygen atmosphere. No oxygen - no fire.
Or you could have an earth like planet, but the intelligent lifeforms evolve in the sea. Imagine if all the land mammals were wiped out by reptiles, on the earth, after some had returned to the sea. At some point, you might expect one of the marine mammalian species to achieve a very high level of intelligence. With no fire. No special atmosphere needed.
