Oxygen Holocaust in Space?

Hello everyone,

So I'm currently building a Space Opera world, and I'm planning on setting it in a part of the galaxy where a lot of new planetary colonies are being formed, new frontier, etc. However, this part of the galaxy used to be the home of a thriving, space-faring alien civilization that, through the intentional and unintentional actions of the human government, human corporations, and human colonists, was brought to extinction/near-extinction (basically, like European colonization of the New World). However, I'm having trouble constructing a mechanism for it.

One idea I had was inspired by the Oxygen Holocaust in the Early days on Earth, where the vast majority of life died because of the introduction of Oxygen which was toxic to most of them. Would it be plausible that a sentient race could have evolved on another world that didn't have oxygen and then have it so that they're "fatally allergic" to oxygen? How would a species that doesn't breath oxygen look like? How could oxygen be introduced to the population by human action?

edited 9th Apr '18 2:52:00 PM by Ludlow

First things first. "Not having oxygen" is impossible; it's one of the lighter elements that is found in relative abundance throughout space. It's always going to be present in planetary formation and in the form of water ice on bodies all over a solar system, plus many other compounds. While it's possible to debate whether life requires carbon compounds and could potentially evolve amid a silicon environment, it is widely believed that liquid water is a requirement for any sort of life to be found anywhere in the universe.

What you probably mean is aliens that do not live in an oxygen-rich atmosphere, having a biochemistry that is based on other molecules besides free oxygen. The good news is we have an abundance of that sort of life on Earth, called plants. Also, anaerobic bacteria and the strange life forms found near thermal vents on the ocean floor, among others.

To many life forms on Earth, oxygen is a deadly poison, because it breaks down organic compounds. Aerobic life on Earth evolved to use oxygen, and it had to deal with that problem to do so. This was outweighed by the benefits of oxygen respiration, namely access to a much greater abundance of energy.

It's not entirely unreasonable to imagine that sapient life might have evolved using something other than oxygen as a catalyst to convert food to energy in its cells. It would have radically different biochemistry, of course. However, it's hard to imagine that oxygen would be some kind of instant-death gas. There's always going to be some oxygen in the environment, just not much, because it binds readily to other molecules. (One likely sign of Earth-like life on other planets is the presence of abundant atmospheric oxygen.)

If Earthlings come to visit, they'll have to bring their own air supply, of course, and inevitably some oxygen would escape into the atmosphere of the aliens' worlds. But it wouldn't be a lot and, without something to actively replenish it, it would very quickly react with other molecules and become harmless. It took millions of years for plants to fill Earth's atmosphere with oxygen to the point where aerobic life could evolve. A puny little human colony isn't going to have much effect on an existing biosphere.

Any alien visiting the humans would similarly have to bring its own atmosphere with it, since ours would likely be highly toxic (and vice versa), but it's not going to cause some kind of extinction event. If humans got aggressive with their terraforming and started trying to create an oxygen-rich atmosphere on a planet that's already inhabited by an incompatible sapient species... well, there would be quite the justification to wipe them out.

edited 10th Apr '18 4:25:16 AM by Fighteer

What about this? Only on a wide scale.

One possibility would be for human plant life to take hold (accidentally or otherwise) on an alien world with an atmosphere rich in carbon dioxide. Over a long, long, long period of time, the oxygen levels in that atmosphere would increase. If the native life were unable to recognize or deal with the intrusion of Earth life, then they could well be poisoned slowly, but, as I said, it would take thousands or millions of years.

Part of the reason for this kind of question is that most people don't appreciate just how big a planetary biosphere is. The mass of Earth's atmosphere is calculated to be 5.1480×10^18 kg [1]. That's five billion trillion tons. It doesn't change composition overnight, absent catastrophic events like a supervolcano eruption or a massive asteroid impact.

edited 10th Apr '18 6:47:59 AM by Fighteer

I dont see it happening by accident, unless the aliens are unbelievably clueless.

On purpose is another story... literally.

Interestingly, NASA does have very significant concerns about contaminating other planets with Earth life, although it's not plants they're worried about but microbes. Any spacecraft that will land on another solar system body or enter its atmosphere must meet certain standards for sterilization. Our Mars landers are deliberately set down far away from any known or suspected bodies of water or other parts of the planet which have a high probability of containing life, lest germs from Earth get loose and create some kind of microbial holocaust by accident.

Laboratories have also been hard at work identifying Earth microbes that could potentially survive in environments like those of Mars, Jupiter's moons, and such. It would be ironic if our first discovery of life outside Earth turned out to be carried there by the very probes we sent to look for it, and doubly ironic if our life killed off the native life before we could identify it. One of the reasons why the Cassini probe of Saturn was deliberately destroyed in the planet's atmosphere was the concern about it crashing on a moon and contaminating it.

So, there definitely are scenarios in which Earth could spread some kind of horrific contamination to other worlds that destroys the life there. They're unlikely, but we are actively planning for how to prevent them. Any such destruction would take a long time, though, and such scenarios don't take into account the possible presence of sapient aliens who would be able to figure out what's going on and stop it.

edited 10th Apr '18 7:01:32 AM by Fighteer

I see, thank the feedback guys.

So, the basic skeleton of what I want to happen is this: space faring species once existed in this part of the galaxy, had huge advantage over humans because they don't need oxygen to live and can thus settle more planets. Contact between them and humans at first peaceful, with the species allowing human outposts on certain worlds and the trading of various native flora between the two. Then, human based flora causes a massive spike in oxygen on the native world of the species and a few major colonies, This leads to many death before the problem is discovered killing many powerful people among the species and causing a crisis of leadership. The species cut off contact with humans after this incident, souring relations between the two. Then, several mega-corps, with the secret backing of the United Nations (the federation of my universe) begin hostile oxygenation of planets controlled by the weakened species. Although this causes several brief wars, all of which are portrayed to the human public as unprovoked attacks by the species, the species becomes too weak to fight back and falls into an irreversible decline.

By the time the stories start, the species is basically dead, with a few primitive hold outs on distant worlds or hiding in small un-oxygenated pockets of planets now held by humans. The majority of humans think the species is extinct due to plague or infighting, and whenever humans do encounter the species the encounters are usually violent.

So, according to you guys, this isn't scientifically possible. At the risk of sounding whiny: would this be beleivable? I'm making a space opera, so so long as it seems like it could happen I'm ok if its technically impossible. Also, I've thought about making the species plant-like(like fighter suggested) and largely immobile due to having set down roots to grow. Thus, colonization of other planets would have been done by sending seeds on computer controlled ships to other worlds where the seeds would take root. Would this immobility and strange way of colonization be enough to explain the species ineffective response to the oxygen holocaust?

Plants do just fine in oxygen-rich environments; what they need is carbon dioxide. Plant Aliens, while a cool idea, doesn't really pass your test. We also don't have any examples of large-scale anaerobic life on Earth; everything in that classification is a microbe. There's nothing barring Bizarre Alien Biology from occurring in this regard — maybe you have a planet of methane breathers or something, and oxygen screws up their metabolism. Of course, a methane atmosphere might not as easily support Earth plant life. It's a conundrum.

My main objection to the idea of oxygen contamination killing off a species isn't that it couldn't happen but that it would happen too slowly in any "accidental" scenario. It took Earth's cyanobacteria hundreds of millions of years to do the job and several other geological events may have contributed. [1] Frankly, plants alone might not do it; they certainly contribute a lot, but phytoplankton are the main source of oxygen in Earth's atmosphere currently.

Your best bet, rather than a few grass fields going nuts, is to have some kind of large-scale seeding of the planetary oceans with Earth phytoplankton. It is believed that the current stock of chlorophyllic Earth biota can replenish the entire oxygen content of our atmosphere in about 2,000 years, so you'd need billions of tons of the stuff.

Note that the target planet would have to have somehow evolved macroscopic sapient species without evolving an equivalent of plants. This is pretty fantastical, but it would make for a neat story if you could develop it well.

There's also nothing inherently preventing you from imagining an alien biology that's so sensitive to oxygen that it dies in the presence of a tiny concentration. It's your story; go crazy.

My objection is that a space faring alien species wouldnt see this coming a lightyear away. Switch the places for a moment—humans contact an alien species that breath a different chemical than we do. They want to come visit our planet. What's the very first thing we do? Obviously we would test the hell out of their biochemistry to ensure that there is no unforeseen danger to either species in their coming here. I imagine the first face to face contact would occur in an isolated space habitat somewhere.

To maintain verisimilitude, your plot requires that exposure to humans contaminate their environment with something that looks benign upon first examination, but which has unforseen catastrophic consequences later on. Something that takes some time to spread, but kills very suddenly after that initial time period has passed. This sound familiar? I'm describing the behavior of a micro-organism.

Let's say they have never encountered a virus before. Even human scientists have trouble classifying viruses as living things—they are only semi-animate, and if the aliens have never seen this type of microbe before, they might not even know to look for it, or recognize it for what it is until it's too late. A virus could easily have an incubation time long enough to spread itself throughout most of the alien's popuation centers before the first symptoms even appear. And it's inherently plausible—this is basically how European colonists wiped out the Native Americans. Sort of like War of the Worlds except reversed.

The only problem there is the sheer unlikelihood of an Earth virus being able to infect an alien organism. It's not completely impossible, but it is pretty damn improbable. Even on Earth, there are very few viruses that can infect more than one species, and you're talking about one that would cross over not just genomes but planets.

Also, it could be a low-tech sapient species: one that's in the equivalent of our early Industrial era or some such, and hasn't really figured out molecular biology and whatnot. The Native Americans certainly didn't understand microbiology.

edited 11th Apr '18 8:35:24 PM by Fighteer

True, but there are billions of varities on Earth. There are probably tens of thousands of different strains on each human. It only takes one.

It seems that you're talking about entirely different orders of magnitude of probability. Viruses on Earth attack DNA and RNA structures in cells. That's it; they're specialized machines that only work with Earth biochemistry. Why would an alien world evolve with anything resembling the same structures... absent hypothetical scenarios like panspermia, of course?

They would probably have some analogue to DNA that stores information needed to reproduce, but I find it incredibly unlikely that it would use the exact same chemical structure.

edited 12th Apr '18 5:38:49 AM by Fighteer

Cross species virus transfer is something like one in a trillion or so. Typically, they come from domesticated animals like horses and chickens, creatures we have tens of millions of exposures with every day worldwide.

All right, maybe not a virus, but a prion might work. That just requires similar proteins, which is not at all unlikely.

Bacteria would be much more likely to succeed, really. They don't require the machinery of living cells to work; they just eat and reproduce on their own. As long as the environment is suitable and they can find food, they're good.

I thought of bacteria first, of course, but I thought it less pkausible that n advanced alien species would have no idea what they were.

edited 13th Apr '18 2:38:47 PM by DeMarquis

I don't know enough about the relevant fields to know whether this is at all plausible, but in case it is: If the aliens don't recognise bacteria, perhaps it's because biology on their planet doesn't involve cells, as such. I'm imagining something like a fibrous structure on a molecular level. By producing different molecular structures, perhaps with different compounds, they might be able to produced differentiated organs, and thus complex life similar to what we understand.

(Quite how this would work, or where it would store whatever serves for them the purpose that DNA serves for us, I don't know. As I said, I don't know whether this is plausible at all. ^^; )

In this case, they might still have micro-organisms, but perhaps sufficiently dissimilar to bacteria that the latter are missed, or misidentified. On the other hand, they might not have true micro-organisms in the sense of bacteria: perhaps their closest analogue produces macroscopic "mats", similar to some fungi, etc., rather than discrete micro-organisms.

@Ludlow - That plant-based thing would probably work. A race that is both immobile and capable of spreading itself around space like that would make them 'alien' enough that you might be able to avoid actually answering questions about their biology. (Keeping in mind that, IRL, people who keep small plants and animals typically don't have and aren't interested in the really specific how-and-why of each species beyond 'provide food and water X times per day'.)

I would put in a one-line explanation for why such an advanced race didn't consider, ah, what we'd call genetic modification to adapt or be adaptable to new environments with different atmospheres. Dunno about you, but my SF background is full of races that made that decision - or were forced to.