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I have a planet that is mostly inhabited by "animals" that aren't carbon based, with intentions for humanity to eke out a way of living there. Now, easily I could reason that they just HAPPEN to contain proteins and hydrocarbons but I want to see if I can make it even more realistic. Currently, humans and a few parasites they brought with them are the only terrestrial life on this planet. Not even rats came with them (Though a couple of stowaways from other planets did, this is several million years after the modern era.) With that parenthetical in mind, these also aren't homo sapiens I'm talking about, just a human lineage that has also evolved more robust metabolic systems. Without easy access to proteins and hydrocarbons, how can humans survive? Do organic compounds show up in inorganic sources (minerals, synthetics, etc)? Are there alternatives humanity might be able to consume that aren't exactly like those on Earth?

These humans are at a technology level analogous to colonial europe, with SOME scifi thermodynamics in play. I don't think they can simply manufacture their own food this way, and there are narrative reasons they haven't simply turned their parasites into protein livestock (they still think food poisoning comes from "bad vapors." The modern period will change this.) Additionally, life on this planet has evolved to look and act as unlike carbon-based life as possible for narrative purposes (we can say it's to avoid predation.) They need only look and act inorganic, though have incorporated more inorganic compounds into their biochemistry to complete the picture and likely consume more inorganic compounds than not. This leaves room for their own synthetic sugars/RNA to highly resemble carbohydrates and protein without actually being either.

90% of life on this planet is inedible, naturally. Human food sources are intent to come from the few places they can actually get that food. The period of discovery started when humans WERE capable of replicating their own natural food source, while scientific advances allowed for the discovery of local foods. I want to know what those could be like on a chemical level. I've exhausted google searches on "inorganic foods" ad nauseam.

Edits: As per other comments, conditions on this planet are similar to early Earth in terms of geochemistry. There's still oxygen and plenty of oxygen replicating lifeforms. The point of this experiment is to answer "How would humans survive (and answer why they survive) if they, without assistance from technology, were plopped on a superficially habitable alien world."

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    $\begingroup$ To me it seems the answer lies in the specifics of this: "these also aren't homo sapiens I'm talking about, just a human lineage that has also evolved more robust metabolic systems." Judging by the fact that they "still think food poisoning comes from "bad vapors"", I'd say these folks aren't advanced enough to chemically manipulate the environment for their needs. So, they can't produce it, and you say they can't farm it from their own bodies, so what's left is the essential organics need to be harvested from the sterile environment, which they can't because there are none. $\endgroup$
    – BMF
    Dec 7, 2022 at 17:56
  • $\begingroup$ In short, I'm not sure this can be answered because we lack more detailed info about the environment and the humans' capabilities, metabolic and technologic. (And by the time you get around to explaining all that, the answers available to you would likely become apparent.) $\endgroup$
    – BMF
    Dec 7, 2022 at 17:59
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    $\begingroup$ What did they eat while traveling to the new planet? $\endgroup$
    – Jedediah
    Dec 7, 2022 at 19:50
  • $\begingroup$ @Jedediah dry-stored packed food with a long shelf life. The population, started from a colonization effort, underwent severe decline during an event I won't get into the logistics of but was the same circumstance that prompted life to resemble inorganic substances. They didn't necessarily have the means to bring hydroponics with them. Farming efforts were planned but background info (colonization abandoned and colonists stranded) made that go awry. $\endgroup$
    – Quinn
    Dec 7, 2022 at 20:16
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    $\begingroup$ What are the "oxygen replicating lifeforms"? Are they plants? Plants use light and inorganic matter to produce oxygen, protein and carbohydrates through the use of organic molecules and macromolecules, and are themselves organic. Unless your human are not organic life forms, they will die on your inorganic planet; amino acids alone will not support life. We humans need carbohydrates (emphasis on carbo), fats, minerals (presumably present on your planet) and vitamins as well as protein. You need to define the basis of your human life forms. $\endgroup$ Dec 7, 2022 at 20:34

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As currently described, they can't.

No native organic compounds? Then they must synthesize organic compounds from inorganic feedstocks, getting carbon from CO2 or methane or graphite or silicon carbide or something.

They didn't bring any plants or algae with them that can perform that synthesis? Then they must use industrial chemical synthesis to produce at least basic food molecules.

They lack the technology for industrial chemical synthesis?

Then they die.

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  • $\begingroup$ Upvoting because you are right. But now I want you to go to work, LRK. Show us how they can do it, in the most awesome way. I know you can. Stretch first. $\endgroup$
    – Willk
    Dec 7, 2022 at 20:28
  • $\begingroup$ I have decided that gut flora is the answer. $\endgroup$
    – Quinn
    Dec 12, 2022 at 21:31
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Precursor technology

So, when humans first arrived on this planet they had advanced technology, we can assume far more advanced than present day tech. It would make sense that they had portable generators of organic components from CO2 or whatever else. Let's say those were intended as an emergency backup, most food would be produced from farming. Then disaster struck and the technology level of these people has been knocked back centiries. However they still have some of those 'food generators'/'food factories' from early days of colonisation left and they're still operational. They don't understand the technology anymore and can't build any new ones but they still know how to operate the existing ones.

These things are the only source of food for these people (except cannibalism, I expect every member of the community who dies is immediately eaten). This would mean that human population can't grow beyond a certain very small size. Any of these machines breaking down or malfunctioning is a disaster of apocalyptic proportions.

I know it's a bit of a cop out, but as per conditions set out in the question, I can't think of any other way.

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Now, easily I could reason that they just HAPPEN to contain proteins and hydrocarbons but I want to see if I can make it even more realistic.

This is the realistic answer. The four most abundant elements in the universe are hydrogen, helium, oxygen, and carbon. Carbon often combines with oxygen and hydrogen to form carbon dioxide and hydrocarbons, which are volatile and can be lost (which is why the moon is highly deficient in carbon), but a planet with interesting chemistry actively happening (in other words, life) probably hasn't lost its volatiles, and so still has a great deal of carbon.

Also, life forms wouldn't evolve to look obviously different from carbon based life to avoid predation if carbon based life didn't exist there.

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  • $\begingroup$ Full disclosure, mainly environmental storytelling. Carbon-based life DID exist, it was the most abundant life on the planet, until it had a hard reset due to a mostly scifi scenario wherein abstract sentient (non-sapient) beings harvested the carbon compounds from whatever had the most of it. Before you ask, these beings have basal intelligence so taking it from the ground isn't working. The only life that survived was extremely simple which let them sneak below the radar but only surpassed the genetic bottleneck by being good at hiding their carbon molecules within inorganic compounds. $\endgroup$
    – Quinn
    Dec 12, 2022 at 21:22
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Easy. Mimic the chemical conditions of early life on Earth.

Does your planet have water, ammonia, hydrogen, and methane?

If so, you might want to look into the Miller-Urey experiment. In it, scientists showed that these four ingredients, when combined with electric sparks, could be used to synthesize the essential amino acids -- amino acids necessary for life, which cannot be synthesized by the body and must come from an outside food source. So, assuming your planet contains these compounds (and since this human lineage can live there, I take the liberty of assuming it does), you can have any protein you need.

Note that the non-essential amino acids can be produced by the body using carbon, oxygen, nitrogen, and hydrogen atoms obtained from the environment, and thus do not need to come from any outside food source. As long as your life forms have access to some carbon-containing compounds (methane, carbon dioxide, etc.) they can synthesize everything else.

Do organic compounds show up in inorganic sources?

The simple answer is yes, as long as you have the very basic organic compound methane. According to the Miller-Urey experiment, essential amino acids, as well as other organic compounds such as sugar, which is needed to form ATP, could be synthesized naturally under a variety of conditions (think meteorites!), as long as ammonia, methane, water, hydrogen, and energy are present.

For more information on the experiment, I highly recommend this video.

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    $\begingroup$ If they lack the technology for industrial chemical synthesis "mimic the conditions of early earth" is hardly "easy". $\endgroup$ Dec 7, 2022 at 19:23
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    $\begingroup$ The efficiency of the synthesis-by-random-banging process is horrible, terrible, doubleplus ungood. On the other hand, it they have methane it is within the reach of early 20th century chemistry to make sugar and fats. Unfortunately, proteins are also strictly necessary and we cannot synthesize those in bulk even with 21st century technology. $\endgroup$
    – AlexP
    Dec 7, 2022 at 19:41
  • $\begingroup$ @AlexP There are no essential proteins. There are some amino acids that our body does not make on its own that we typically get by breaking down certain proteins, but by in large, if you diet has the amino acids it needs, it does not need protein at all. $\endgroup$
    – Nosajimiki
    Dec 7, 2022 at 19:51
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    $\begingroup$ The Miller-Urey experiment only produced five (?) amino acids, and no sugars. We don't really know what the conditions were like on early earth, but the conditions are not believed to be those proposed by proponents of the Miller-Urey explanation of the origin of life. In any case, humans could not survive in those conditions. we need a different atmosphere. $\endgroup$ Dec 7, 2022 at 20:49
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    $\begingroup$ @TheresaKay The question specifies that the planet has no native organic compounds. Ergo, the ingredients are not present, and the environment is not like early Earth. And if it were like early Earth... nothing descended from humans would be able to survive there anyway, regardless of how much food was available. $\endgroup$ Dec 8, 2022 at 4:20
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They already do it at home

As others have pointed out, amino acids (precursors to proteins and many other complex organic compounds) can be created by electrical discharge (e.g. lightning). However, if this planet does not already contain complex organic compounds but has the necessary precursor elements, this new planet probably is low on lightning. Given their level of technological development, they likely would not know enough chemistry to develop the means to convert inorganic materials to organic ones.

So have ancient aliens endow them with it.

Large swaths of their home planet were for some reason largely devoid of life. A long time ago, a more advanced civilization visited gifted them very advanced machines which could turn rock into food or soil and then left, granting them few or no other technologies and did not give them the knowledge to produce more of these machines. There are only a few dozen of these machines in existence and they have lasted a very long time and are coveted, mysterious, valuable, and therefore powerful political tools. Maybe this crew stole one.

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Agriculture & Artificial Selection.

90% of life on this planet is inedible, naturally.

This naturally means that 10% of life on the planet IS edible. Even here on Earth, there is a huge diversity of plants and animals that if eaten will kill you. Nuts, beans, fruits, meat, etc. all run the risk of containing deadly poisons if you eat the wrong one; so, just like our real ancestors did, your colonist will have to learn on a species-by-species bases what is food and what is not, and they will pass that knowledge from one generation to the next to make sure that people are not just dying left and right from eating non-compatible food sources.

All this said, just because 10% of life is edible does not mean it will stay that way. Humans love killing off things that are harmful or useless to us and cultivating life that is useful. It's kind of our thing. Overtime, your humans will spread killing off all useless local flora and fauna to make room for fields of edible crops and livestock. Because local life is so obviously different than Earth based life, it would be much more easy than it is here on Earth to tell crops from weeds making 100% local life removal relatively easy.

You may lack a bit of biodiversity at first, but it would not be as big of a deal as you think. In many times in history, peasants have lived exclusively off of as little as 2 food sources. As long as you can grow some kind of grain and beans or potatoes and fruit humanity can expand to take over the planet. Also, since you explained that this is a distant future version of humans, a singe species can be selectively bred into a lot of varieties over just a few centuries, much less a million years. Just look up all the modern plants that were bred from mustard or all the different breeds of dog we have. So by your time frame, there should be a reasonable diversity of Earth based plant life.

Where did this life come from if there were no stowaways?

Most of what we eat can also be put into the ground and grown. Whole grains, beans, potatoes, carrots, mushrooms, any fruit containing seeds... the list goes on. Your people may not have come here planning to plant thier food supplies, but any humans smart enough to travel the stars will also be smart enough to figure out that if they put the food they are already eating into the ground, that it will grow.

A million years ago, while these ancestors were seeding thier food, there would have likely been a number of devastating crop failures and mass starvation, but some of those plants and people did well enough, and now they are adapted to the planet's climate and soil conditions.

But would the plant have the elements necessary for life to expand?

If we assume your planet's surface chemistry is similar enough to Earth to not kill humans right out, then you can also assume it is similar enough that the air and soil will be compatible with at least some kinds of agriculturally useful life.

Your air needs to be breathable meaning it needs to contain appropriate amounts of Oxygen. Humans also need water and a certain temperature range; so, we can also assume that precipitous water and by extension, hydrogen are available. That said, a pure oxygen atmosphere with enough gravity to retain an atmosphere would be toxic, so there also has to be an inert filler gas. If this gas is not nitrogen, then there is a very good chance that what ever takes its place is toxic... so it's safe to say we have a temperate world with water and atmospheric oxygen and nitrogen as a bare minimum for humans to survive at all without advanced technology.

The real question is if a silicon-life based world would have enough carbon to sustain Earth based life. The answer is yes. Your planet is actually very likely to have more available carbon than Earth, not less. In the galactic scheme of things, Earth is actually a very carbon scarce planet. Carbon is the 4th most abundant element in the Milky Way Galaxy, meaning that the average rocky planet should have about as much carbon as silicon, but here on Earth, it's 150 times more scarce than silicon. So even if you have silicon based life on a silicon world, Earth Carbon based life is already adapted to this. Ironically, it would be the planets out there with "normal" levels of Carbon that would be most toxic too us.

These facts together mean that any planet a human can set food on and live is pretty much guaranteed to have the 4 major building blocks of organic chemistry. So, even if the local life is silicon based, it does not mean we wont be able to displace it.

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