why alien civilizations could require oxygen

December 6, 2010

Oxygen is a gas we generally take for granted here on Earth thanks to the abundant flora that keeps its levels in our atmosphere nice and high. Not only it is vital for our bodies to power themselves, but it’s essential for quite a bit of our technology. Metallic alloys and plastics on which we rely to build everything from buildings to spacecraft, require fire to smelt, mix, and mold. Even something as basic as pottery and bricks still require an oven with a steady flame, and cooking food to kill bacteria and parasites, would be impossible without a nice, roaring fire. And if you want fire and heat without having to deal with a violent volcano belching noxious fumes, you need to have oxygen. I learned this as a kid in science class, giving it little thought until recently, when my girlfriend asked me if aliens living on a planet which didn’t have oxygen could ever develop a civilization as we know it since they’d never be able to start a fire to cook their food, much less build advanced technology.

Now, I really didn’t know how to answer her question, but after giving it some thought, I think she might have a very interesting point. After stone tools, the first major leap forward for humans was fire. With food that was far safer to eat and much easier to chew and digest, we could get more from our nutrition. On cold nights, a good fire would warm our caves and huts. And fire allowed for the next leap forward, the invention of metal tools and the ability to create lighter and more durable weapons to defend our farms and hunting grounds. And you may even say that fire was one of the technological catalysts for the emergence of human civilization as we know it today. For fire, though, we needed to have oxygen in our atmosphere. So what would’ve happened if the Earth produced macro life that didn’t need oxygen and the reactive gas was present only in very trace amounts? Say goodbye to caves that could be warmed on demand, creating custom tools from metal, or even making basic pottery wherever you want. And even if you could just walk up to a superheated volcanic vent, you would have a lot of trouble making tools that wouldn’t burn up or melt from the magma’s radiant heat.

Even if you’re extremely creative and manage to tap into a geothermal source, you can forget about controlling the temperature to create exactly what you need because it really isn’t as simple as moving what you need to heat to the right distance from the magma. All sorts of environmental factors would affect the heat that’s being put out of the vent and the exposure to noxious gases would be a major problem for any macro life. Basically, you really need to get heat on demand if you want to build cities close to easily traversable terrain, rivers, and seas, and if you want to make materials that require a very precise recipe, materials you can use in everything that’s needed to build computers, radios, TVs, lenses, and mirrors, you’re out of luck. Does that mean that we have to look for a world with oxygen in its atmosphere if we ever want to find alien cities, and not because we want to find high levels of atmospheric oxygen as a requirement for life, but because we’re looking for species that can discover fire? Maybe there’s a chemist in the house who could set us straight and let us know if there may be another way of creating a controllable heat source in an atmosphere without oxygen? And what do you think? Can one have a technological society without having to discover how to handle fire first?

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  • Interesting thought. I wish I had an answer, and will watch your posts for someone who does.

  • reknaw

    Good point, but remember that oxygen just takes part in an exothermic reaction, ie a reaction that produces an excess of energy at the end and it is that energy that for example melts the metals in a blacksmith’s oven (thermal energy becomes kinetic energy of the metal atoms).

    Therefore, in the absence of oxygen you only need to find another (efficient) exothermic reaction. You can see some examples in the wikipedia link I pasted above.


  • Greg Fish

    I understand that you can generate heat without oxygen, but the question here is what reaction would be as easy to discover and as convenient to replicate as fire for some budding, would-be alien society living in a cave on a distant world? When you have the tools, you oxygen can be optional, but here we’re explicitly saying that our hypothetical aliens won’t have them.

  • reknaw

    > what reaction would be as easy to discover and as convenient

    That really depends on which chemicals are available in the aliens’ planet. Without specifying that (ie the chemistry of the habitat), the whole discussion is moot. Also, I didn’t mention any tools.

    My (educated) guess is that in many given scenarios you would be able to find some sufficiently exothermic reaction using only raw materials readily available in the habitat. The parametric space is so large that a lot of interesting possibilities may occur. On the other hand, I could also imagine a species doomed to never achieve advanced technology because they won’t have access to metallurgy, rare earth minerals etc.

  • Paul

    To get advanced (intelligent) life, you would need enough energy to run energy hungry organs like the brain. (Some kind of distributed vegetative intelligence is unlikely to be tool using.) That means something like oxygen, even if it’s not actually oxygen. (Say, Chlorine, Fluorine, etc.)

    The only way I can see you having enough energy for intelligent life, but without the ability to make fire, would be a water dwelling intelligence. Super Dolphins, smart squid, etc.

  • Pierce R. Butler

    Well-behaved, metal-rich volcanic flows might get some anaerobic Oggs and Thaggs started with serious technology, and they could, on many planets, set up arrays of solar mirrors to smelt and smith with higher precision.

    With the right minerals in their primordial stew, photovoltaic-based life forms are just barely conceivable, and might be just a few mutations away from developing cybernetic capabilities and thus intelligence (probably well pre-adapted to technological talents, and respect for lightning gods).

    But a world without oxygen is a world without photosynthesis (at least by chlorophyll), and thus in dire need of a bioaccumulative process, or at least a way to sequester greenhouse gases or keep them corked up subsurface indefinitely (or a planet somehow geologized without significant CO2 in its crust). (Well, an atmosphere without oxygen is by definition one without CO2, unless you mean without free oxygen…)

    Though he didn’t present metabolic processes in sufficient detail for my nerdy tastes, Hal Clement in Iceworld featured some sulfur-breathing aliens who would probably be able to answer y’all’s questions. Having been written back in the day when Mercury was believed to be phase-locked with the sun, they launched their nefarious Earthly project by establishing a base on that well-lit planet right in the center of Sunside. They started the project with a shaped H-bomb nicely calibrated to create a reflective-walled parabolic crater, the focal point of which was deemed warm enough to be comfortable; the thought of free oxygen scared them @#!+less.

    Paul: … a water dwelling intelligence. Super Dolphins, smart squid, etc.

    I’ve speculated earlier here that those may have a much better chance of evolving than large-brained land-walking creatures.

  • Keith Harwood

    You don’t have to guess at a replacement for oxygen, you can assume it straight away. Our oxygen didn’t come with the original package, it was made by life. For an alien planet you can assume that any autotroph will create a chemical disequilibrium in its environment. If the autotroph is primitive, as on pre-oxygen Earth, the disequilibrium will be small. But if it is primitive, there aren’t any clever aliens to exploit the disequilibrium. For advanced life you can expect efficient autotrophs creating a disequilibrium and efficient heterotrophs reducing it. Reactions reducing it are exothermic and some of those reactions serve as fire.

    So, while it is interesting to speculate on what chemical reactions may replace oxygen fire as a civilising influence, it is not necessary. You can be sure that if there is alien life sufficiently complex to be capable of civilisation it will have something to play the role of fire and that that something has existed throughout most of its evolutionary history.

  • Gregory Andrade

    True one would need a heat source, but it doesn’t necessarily need to be oxygen and it doesn’t need to be required for the aliens respiration system. On the other had too much of a flammable gas would spell disaster for any of the local residents and said gas could alter the climate rather like when oxygen was introduced on Earth causing a super ice age known as the Snowball Earth. I could defiantly see another civilization on a methane driven hot house planet.

  • RicoLouis

    A Florine or Clorine enviroment would support combustion but it raises raises the question of what would protect them from uv rays, no oxygen means no ozone. You also need Oxygen to make water. H2O which is the building block of life on earth. A large portion of or oxygen comes from the oceans.