Take a world with the same physical characteristics as Earth, but where biochemical development has "rolled the dice" differently in some cases.

  • The simple chemistry are the same compounds in slightly different proportions. The air consists mostly of nitrogen, oxygen, argon, carbon dioxide. The water is ordinary H2O, with dissolved salts in the oceans and the trace organics one would expect from the ecosphere (see below). Sand and rocks are made from silica and carbonates, mostly.
  • There is carbon-based life which looks much like life on Earth. Simple organic compounds like ethanol or butane are the same. The differences are in the more complex compounds.
  • Life includes something like photosynthesis-based flora and mobile fauna. Details differ, of course.

What are the problems if humans want to raise crops and lifestock on this world outside a sealed greenhouse?

It seems obvious that humans could sterilize soil and bring it into a greenhouse, but that is not necessarily easier than raising crops in a space station.

  • $\begingroup$ Which VTC reason should I pick? Focus, because there's three questions rather than one. Needs clarity, because obviously humans that evolved on your world would live just fine in the environment and it's impossible to know what you're fishing for with a question like, "what does it take to raise crops?" (rain, sunlight, fertilizer, and time, as always, right?) Story-based, because "what else?" is always up to you, the author (it's your world, you tell us). The "too broad" reason's been dumped, so I can't pick that one, but the question is too broad. What is your single, specific question? $\endgroup$ – JBH Oct 4 '20 at 5:53
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    $\begingroup$ @JBH, do you seriously count question marks to determine focus? I could have written. "I have wondered if they would need sealed greenhouses or if they can plant outside." No question mark, but no significant difference, either. Or I could have deleted the last paragraph and written "I have thought about some simple fixes, but asking about them would remove focus." The question here is "how do humans, crops and livestock do in this enviroment?" And if I knew all the realistic biochemical pitfalls, I wouldn't have to ask here, hence the "what else?" $\endgroup$ – o.m. Oct 4 '20 at 9:06
  • $\begingroup$ No. I count disparate questions. Of the original four, three were barely related (and "what else" wasn't asking for pitfalls, it was appended to your biochemical conditions list). You know the rules better than I do. One-specific-question/one-best-answer and SE is not a discussion group. Thanks for the edit, though. It's a much better question. $\endgroup$ – JBH Oct 4 '20 at 9:24
  • $\begingroup$ What does the terrain and water cycle look like? And how about the microbes? Are we assuming that all of the microorganisms are either helpful or harmless to humans and terrestrial plant life? What kinds of plants are we cultivating and where do the seeds come from? Soil is mostly live, organic matter so its composition (“health”) is very important with regards to extraterrestrial agriculture. $\endgroup$ – HolocronCollector Oct 5 '20 at 3:23
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    $\begingroup$ @HolocronCollector, I'm worried about those questions but adding them would make this too broad. There are alien microbes. They (probably?) won't be able to live in human organisms. Nitrogen is still nitrogen, ammonia is still ammonia, so nitrogen-fixing should work the same. Terrain is what you get when you get several billion years of weathering on a tectonically active planet, that means it varies greatly from place to place. Deserts, plains, rainforests ... $\endgroup$ – o.m. Oct 5 '20 at 4:57

With an alien world, alien biogenesis and presumably billions of years of alien evolution the local flora and fauna might resemble their Earth counterparts to some extent but their biochemistry would be scrambled compared to that from Earth.

Chance has a big part to play in evolution and with slightly different starting conditions the result would in all likelihood be biochemically different. Hard to say how different but such life would probably rank somewhere between inedible and toxic.

In basic terms all metabolic pathways are scrambled. Lots of common small molecules, but the larger molecules would mostly be different and their are millions of them in the biosphere this is just a small part: https://www.sigmaaldrich.com/technical-documents/articles/biology/interactive-metabolic-pathways-map.html

The alien life would be well adapted to the alien conditions, Earth life would not. There would be serious difficulties with weeds, although with research it should be possible to find something that was deadly to the native life but didn’t harm Earth life. It might take time to find it, it would probably need to be reapplied regularly and some of the “weeds” might become resistant to it.

There could be physical as well as chemical difficulties – perhaps the air is fall of a million fold more spores than on Earth that clog lungs – but there might not we don’t know.

Letting livestock anywhere near the native flora would probably not end well as Earth based fauna are adapted to Earth and would be tempted to eat whatever they perceived to be edible which would almost certainly be a mistake.

For things like wood there would probably be little immediate danger as it would probably primarily be an inert primarily structural element, but saw dust might well be toxic.

  • $\begingroup$ If lifestock is a problem, the answer could be eating fish from tanks and chicken from cages. But it would also be a problem once the colonists have children. Toddlers will eat anything. $\endgroup$ – o.m. Oct 4 '20 at 14:13

The "bricks" are the same, as you state. This means that, with a proper bacterial ground, "our" plants can grow, for example by having nitrogen fixing organisms. This would mean that the colonists would have to take with them not only seeds, but also sample of the grounds to be sure that all the needed microorganisms can be present.

Probably a sterilization of the ground before planting would give better chances to "our" organisms, since it would take out competition for the bricks.

For the rest I would exclude cross pathogenic effects: since the DNA basis are different, a cross infection would not find a way to propagate because the instructions of the infector would not be executable by the infected.

That however does not rule out toxic effects by alien molecules.

  • $\begingroup$ Of course soil sterilization (and does that mean sealed greenhouses, too?) makes the settlement much more complicated. So if it is just a question of better chances, would the choice be between a small cultivated area with healthy plants and a large cultivated area with sickly plants? $\endgroup$ – o.m. Oct 4 '20 at 5:41
  • $\begingroup$ @o.m., as far as I know colonists always starts small, to learn and try to grow big. $\endgroup$ – L.Dutch - Reinstate Monica Oct 4 '20 at 5:45

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