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If / when humans finally reach another planet that has life, what are the main challenges facing humans living in the open trying to colonise a planet with an alien biology?

Assume that the planet closely resembles the earth in all respects except that its evolution has run a completely different course due to random variation. Plants and animals exist and oxygen and carbon dioxide are consumed and released as they are on earth, but all metabolic processes are carried out by an entirely different set of organic chemicals. No DNA and no proteins exist. This different set of organic chemicals range from the harmless to the toxic and everything in-between. All life forms are inedible and most are poisonous to varying degrees. There are no sentient inhabitants.

edit Assume that the environment (plants animals and soils) are mildly toxic to all earth based life. There are some non-toxic (but inedible) species and a few very toxic species. Think of the environment containing many of the less toxic reagents from an organic chemistry lab.

Assume that most fine particulate matter such as dust and the equivalent of pollen are either non-toxic or easily filtered out by a simple face mask.

Slarty
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    This feels too broad. What if the pollen analogue was toxic and absorbable through the lungs? Then the answer would be "no." If people have to consume the alien life typically in order to be poisoned then they'd probably be fine once they identified the contact poisons like our poison oak/ivy. Also do the toxic organic compounds leach into the Earth plants like food coloring in white flowers? That might make everything grown locally inedible... In general though it could be as toxic or not as you choose. – Erik Oct 05 '17 at 21:55
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    @Erik, it probably won't be complex things like pollen analogues that kill you. It'll be the plant that gives off hydrogen cyanide as a signalling chemical, or the animal that excretes arsenic-rich waste, or... – Mark Oct 05 '17 at 22:17
  • @Erik I have added an edit to clarify the particulates issue. None of the alien life can be consumed. As a side note I suspect that the situation I describe might be a better approximation to what we might actually encounter than many science fiction settings that assume evolution has followed roughly the same lines as it has on earth. – Slarty Oct 05 '17 at 22:45
  • @Mark I agree. I was reaching for some particulate that would be common in the air. The point I was trying to make is the same as yours. There are untold number of things and vectors for those things that you could make it as toxic or non-toxic if as you want. Even the latest edit "environment containing many of the less toxic reagents from an organic chemistry lab" has problems. I'm no chemist but I know there are mildly toxic chemicals that can be mixed and become toxic. Also I have bathroom cleaning agents that are fine to breathe while cleaning but I couldn't breathe an atmosphere of them. – Erik Oct 05 '17 at 23:09
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    This is still too broad. How long is our test? What resources have our heros? If left open-ended and without resources, our heros are dead a couple of days after the food they packed in runs out. Resources give them days to forever. Do they have the tools to filter the water? If not, they're dead in hours depending on the exact nature of the flora and fauna. What are our heros doing here? Why did they come? How are they prepared? – JBH Oct 05 '17 at 23:59

5 Answers5

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Earthify it.

Earth humans have a very powerful method to make such a planet more liveable: earth dirt. The minute a spoonful of dirt is dropped onto this planet, Earth micro-organisms will begin vigorously competing for space and resources with the natives. Humans can help their kin by doing things like sterilizing large swaths of soil before introducing the earth microbes.

Microbes are formidable competitors, and in an ecosystem not evolved with these creatures, they might run roughshod over the natives. By natives I mean native soil micro-organisms. And the converse might be true. I suspect that either way, within a few months, microbally "terraformed" soil could grow crops outside. Within a few years large swaths of the planet soil will be unstable mixes of earth and non-earth organisms.

As regards macro-organisms this could cut both ways. Human immune systems are remarkably flexible in their ability to defend us against weird pathogens. The immune systems of this world's natives might be equally flexible. If not, these organisms become substrates for growth of micro-organisms that want their raw materials: organic nitrogen, reduced carbon, water and sun-exposed surface area.

I would not bet against the earth creatures. I bet that this planet is a 75% / 25% earth alien mix within 20 years.

Willk
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Macro-scale effects won't be a problem. Humans have dealt with everything from fire ants to saber-toothed tigers. A spacefaring civilization with the willingness to engage in scorched-earth tactics can easily deal with attacks by any non-sentient alien life-form.

The problems come from indirect effects. If your plants use hydrogen cyanide as a chemical signal to attract pollinators, humans are going to have a hard time surviving their first spring on your planet. If your animals use organomercury compounds in their biochemistry, every carcass needs to be treated as hazardous waste. If you've got a bacterium that excretes purified arsenic as a waste product, any dust storm is potentially lethal.

A wildly different biochemistry such as you describe won't harm humans the way Earth biochemistry does. There will be no alien diseases, no allergies, no venoms. It's not the hostile animals or the big, complicated proteins that will kill people. It's the small, simple molecules that are the threat.

Mark
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If there's oxygen and carbon dioxide in the air then humans could likely stay out in the open. If there is no way to make the local plants edible through cooking, colonists could always bring their own crops. If the chemistry of the soil is radically different then food may need to be grown in a raised garden bed, or maybe in beds suspended in the air inside greenhouses.

You didn't mention if this planet had water or not. If they can't get it from their surroundings then lots of water would have to be brought in, for the settlers and to grow their food. Not to mention if herd animals are brought, you need to import even more resources to maintain them as well.

All in all, a small outpost could probably maintain itself on these imported goods, but a huge scale colony may not be worth the work if nothing can be done to manipulate the resources already there.

Lot-Of-Malarkey
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Maybe.

Assume that the planet closely resembles the earth in all respects except that its evolution has run a completely different course

This means that gravity, atmosphere pressure and contents as well as humidity are Earth standard.

It still isn't enough. The main dangers I see are insects - while biologically incompatible, they could still give someone anaphylactic shock, or be supplied with a poison that works on humans and feel humans look or smell like enemy (there might be workarounds, like dressing in Cadzie blue) - and dust (mainly pollens and vegetable matter, but plain dust too, Earth similarity notwithstanding).

If the air contains enough allergens, living outside might require breathing apparatuses or even pressure suits. That is, it would be impossible. Allergy could go all the way to toxic effects like poison ivy; one breath and the trachea's lining inflames and swells, leading to death by asphyxiation.

All kinds of critters and bug could be present that could kill humans straightaway (think legionary ants).

LSerni
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Look at the concept of chirality. Even if the alien ecosphere uses the same elements as Earth, it may well be that simple organic molecules like sugars are built the "wrong" way. For instance, L-Glucose cannot be metabolized.

People might starve with full bellies if their food supply is contaminated with these "useless" molecules.

o.m.
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