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I would like my human colonists to settle on the high plateaus (2500-3000m above sea level) of my planet thus never meeting the civilization living in the lowlands (in a huge forest so they aren't visible from above), until settlers find evidence of them and decide to see what's going on down there. The thing is that I need a reason why they wouldn't go to those lowlands earlier, so something that makes the descent difficult but not impossible, and also why my civilization wouldn't develop on the plateau. Here are the main ideas I had:

  • Hostile environnement at the edge of the plateau. I don't think it could stop my civilization, humans lives in deserts and very dense rainforests with plenty of deadly animals, nor why wouldn't my colonists just go through it with their technology but if you have any idea how it could work it's ok

  • Oxygen levels (or any other gas). This my favourite idea but I'm not sure it would work. It's easy to make my civilized species highly oxygen-needing so they can't live on the platea. For my colonists I know that high pressure of most gases are dangerous but is there any effect that is just very uncomfortable, like the light hypoxia you feel when above 3000m or so?

If you have something that could make the second idea work it's perfect, otherwise just find something that could fix the first or a brand new one.

Background:

My story takes place in the 22nd century. The colonists are mainly scientists who came here to explore and study the planet. There are 50 and they have buggies, guns and an helicopter. A few months before the evidence of alien civilization, all the AI in these are destroyed by a computer virus which came in a message from earth (but it might be an e-mail they didn't open before). The purpose of the virus was to destroy all the AI used on earth and it was send in basic telecommunications from NASA. Now they just have some basic technology like solar panels and everything that didn't have any AI in it. I'm not sure why wouldn't they have pressurized air tanks. Basically they had advanced technology but no incentive to go to the lowlands, then later they have only basic technology but must be able to go in those lowlands, and I'm wondering why they didn't have incentives to do it before.

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You have already solved the problem via your backstory.

50 people, alone on a planet, with less than the equipment they planned to have, would have to take on a defensive posture. With so few people, they must have been planning to depend on robotic workers which would have been controlled by the AI. Now that that is not an option, they have to learn how to do all of the manual tasks which the now-useless robots won't be doing.

  • They need to get the fields planted before their food stocks run out.
  • They need to build winter-proof shelters while the weather is warm.
  • They need to repurpose all of the formerly AI controlled equipment to work under human control.

Nobody has time to do any exploring of the lowlands or anywhere else.

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    $\begingroup$ "Get the fields planted?" Surely they would use hydroponics or aeroponics to grow food, or food synthesizers. "Build winter-proof shelters?" You mean assemble the prefabricated shelters they brought with them. $\endgroup$ – M. A. Golding Sep 15 '18 at 16:08
  • $\begingroup$ These are scientists not permanent colonists; anything by way of supplies or shelter they didn't bring with them but find they need is going to be extremely problematic (and possibly fatal) for them. I agree that the lose of their AIs is probably going to cripple them though. $\endgroup$ – Ash Sep 15 '18 at 17:18
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    $\begingroup$ @MAGolding, I assumed by the 182 year deadline imposed by the 22nd Century timeframe, and by the fact that only 50 living souls were brought along, that we are still dealing with weight restrictions for interstellar transport. ( In my opinion, the idea that we will be interstellar by then seems optomistic, so weight restrictions seems like a reasonable assumption. ) Prefab Shelters and Food Synthesizers seem like a luxury when you are heading to a planet that already has trees. $\endgroup$ – Henry Taylor Sep 15 '18 at 19:29
  • $\begingroup$ But why didn't they explore those lowlands before the virus ? $\endgroup$ – Jean-Abdel Sep 15 '18 at 19:52
  • $\begingroup$ @Jean-Abdel, computer viruses are very different from biological viruses. They are deliberately created and target specific types of computers. Since we are talking a freshly colonized planet, I would assert that the only computers on the planet are going to be the ones that the scientists brought with them. As such, the virus must have come along with the colonists. It must have been created on the scientists' home world and been mistakenly included aboard the ship. If that is the case, there was no "before the virus" on the planet. The AI was probably dead before the ship landed. $\endgroup$ – Henry Taylor Sep 16 '18 at 6:27
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Nitrogen narcosis.

Poul Anderson had a setup like this in New America.

https://openroadmedia.com/ebook/New-America/9781497694316

Civilization on Rustum has come a long way since its early days, when a few brave colonists traveled twenty light-years from Earth to found a society, New America, on the principle of personal liberty. Some call themselves Constitutionalists, others Jeffersonians, but whatever the title everyone can agree: Rustum has a problem. With one-and-a-quarter times the gravitational force of Earth and a host of inedible flora, Rustum is most habitable on its highlands, leaving the lowlands sparsely populated and creating a great imbalance on the planet.

Dan Coffin, an original settler of Rustum, agrees to join an expedition back to the lowlands, where he is one of the rare individuals who can survive in the dense air without a helmet. New America follows Coffin’s endeavors to build a new life with a wife, children, and an effective governing body that can help give the lowlanders not only survive, but thrive.

But why, specifically, is the dense air problematic? The easiest way is to have unadapted persons suffer from nitrogen narcosis.

Nitrogen gas under pressure can make you feel really drunk or really high.

The most dangerous aspects of narcosis are the impairment of judgement, multi-tasking and coordination, and the loss of decision-making ability and focus. Other effects include vertigo and visual or auditory disturbances. The syndrome may cause exhilaration, giddiness, extreme anxiety, depression, or paranoia, depending on the individual diver and the diver's medical or personal history.

This is why people doing deep dives replace some nitrogen with helium in the mix they breathe. Nitrogen narcosis is good for a narrative because if you have characters which have this happen, they can act weird in different ways that help the story. More fun than having them puke or itch.

Nitrogen narcosis starts to happen at 2-3 atmospheres pressure which you can achieve in your lowlands by having more gas in the atmosphere total, or having higher gravity.

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  • $\begingroup$ They said at least 4 atm for really bothering effects, 2-3 atm is only mildly annoying and it looks really huge, I would need a very high gravity to make a real difference between plateau and sea level pressure. Is there any other gas that have this narcotic effect at lower pressures? $\endgroup$ – Jean-Abdel Sep 15 '18 at 20:11
  • $\begingroup$ You do not need high gravity. Venus has gravity 80% of earth but surface atmospheric pressure is 90 times that of earth. If you have more gas in the atmosphere you have more atmospheric pressure. Just add gas to your world (nitrogen would be fine) until atmospheric pressure is what you need. $\endgroup$ – Willk Sep 15 '18 at 22:41
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    $\begingroup$ High gravity is needed to make a difference so plateaus will be pretty comfortable and lowlands absolutely not $\endgroup$ – Jean-Abdel Sep 16 '18 at 9:13
  • $\begingroup$ @Jean-Abdel High gravity will also tend to make the plateaus lower so it doesn't help as much as you think. You probably just need less water so you can get down further before you hit ocean. $\endgroup$ – Tim B Sep 17 '18 at 12:29
  • $\begingroup$ Actually it's the base of my setting, sea level is already 3000m lower than on earth and colonists settled on the continental shelf. $\endgroup$ – Jean-Abdel Sep 17 '18 at 18:53
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You say the explorers or colonists

settle on the high plateaus (2500-3000m)

of your planet.

2500 meters is 8,202.1 feet, while 3000 meters is 9,842.52 feet. You didn't say if 2,500 to 3,000 meters is the height of the plateaus above sea level or above surrounding terrain, which could have a considerable elevation itself.

It is possible that the plateaus are surrounded by high mountains that it is difficult to cross.

the barometric formula, sometimes called the exponential atmosphere or isothermal atmosphere, is a formula used to model how the pressure (or density) of the air changes with altitude. The pressure drops approximately by 11.3 Pa per meter in first 1000 meters above sea level.

https://en.wikipedia.org/wiki/Barometric_formula1

Wikipedia lists 67 settlements between 3,700 meters (12,100 feet) and 4,700 meters (15,400 feet) and 7 settlements between 4,710 meters (15,450 feet) and 5,130 meters (6,830 feet).

https://en.wikipedia.org/wiki/List_of_highest_cities_in_the_world2

Altitude sickness typically only occurs above 2,500 metres (8,000 ft), though some are affected at lower altitudes.2 Risk factors include a prior episode of altitude sickness, a high degree of activity, and a rapid increase in elevation.3 Diagnosis is based on symptoms and is supported in those who have more than a minor reduction in activities.2[4]

People have different susceptibilities to altitude sickness; for some otherwise healthy people, acute altitude sickness can begin to appear at around 2,000 metres (6,600 ft) above sea level, such as at many mountain ski resorts, equivalent to a pressure of 80 kilopascals (0.79 atm).

High-altitude adaptation in humans is an instance of evolutionary modification in certain human populations, including those of Tibet in Asia, the Andes of the Americas, and Ethiopia in Africa, who have acquired the ability to survive at extremely high altitudes. This adaptation means irreversible, long-term physiological responses to high-altitude environments, associated with heritable behavioural and genetic changes.

Nevertheless, around 140 million people, just under 2% of the world's human population, live permanently at high altitudes, that is, at heights above 2,500 metres (8,200 ft) in South America, East Africa, and South Asia. These populations have done so for millennia without apparent complications.[9] The overwhelming majority, over 98% of humans from other parts of the world, normally suffer symptoms of altitude sickness in these regions, often resulting in life-threatening trauma and even death.

Studies on the detail biological mechanism have revealed that adaptation of the Tibetans, Andeans and Ethiopians is indeed an observable instance of the process of natural selection in acting on favourable characters such as enhanced respiratory mechanisms in humans.[10][11]

https://en.wikipedia.org/wiki/High-altitude_adaptation_in_humans 3

Humans can get reverse altitude sickness when travelling from high altitudes to low altitudes.

If about 2,500 to 3,000 meters altitude on your planet has air pressure close to sea level that is comfortable for humans, then altitudes close to sea level on your planet should have uncomfortably high pressure.

If your alien planet has a slightly higher gravity than Earth, perhaps about 1.05 or 1.10 that of Earth, it might not be high enough to affect the health of the explorers too much, but it will certainly make them a little uncomfortable. And the higher gravity will cause the planet's atmosphere to squashed down a bit more than Earth's, so the air at sea level will be denser relative to 2,500-3,000 meters than it would be on Earth.

And it is possible that the natives live in a dense forest surrounding a large lake in some depression which is hundreds of meters below sea level on this planet and so has an even higher atmospheric pressure.

Thinner air at higher altitudes tends to be cooler, so it is possible that the high plateaus seen rather hot for humans and the lowlands where the natives live seem even hotter and more uncomfortable.

All gases in Earth's atmosphere or any atmosphere similar to Earth's will become toxic at high enough concentrations.

78 % nitrogen? It can be toxic at higher concentration. 0.93% argon? It can be toxic at high enough concentration. 0.04 % carbon dioxide? It can be toxic at high enough concentrations. 1 % water vapor? It can be toxic at high enough concentrations.

Even the 20.95 % of oxygen in the atmosphere, vital for human survival, can become toxic at high enough concentrations.

So possibly the atmosphere has higher concentrations of certain gases than Earth's atmosphere does, and the concentrations of those gases are survivable in the thin air on the plateaus but eventually lethal in the denser air at the low levels the natives live in.

If intelligent aliens were discovered who lived deep underwater, going deep underwater to meet them could be a problem. If the colonists don't have submersible vehicles they may have to scuba dive to the depths that the aliens live in. Because water pressure increases very rapidly with depth, scuba divers have to increase the pressure of their breathing gas to compensate, or they won't be able to expand their lungs against the pressure.

Air is used down to 40 meters or 130 feet. Various gas mixes are used to dive to greater depths. Below the depth where any air mix is safe hard suits or submersibles have to be used, which explorers and colonists might not have.

If the natives live on land, the problem is how to make the altitude difference great enough that their air is so thick that breathing it would be lethal for humans, or at least very uncomfortable. It is possible, depending on the exact atmospheric composition of your planet, that a difference of 2,500 to 3,000 meters will be enough.

09-17-2018 When I was a child I once read a story by Ernst Thompson Seton where a depressed grizzly bear committed suicide by going to the "valley of death". It might have been based on the "Valley of Ten Thousand Smokes" in Alaska. But the volcanic fumes in the fictional valley were deadly.

Obviously there could be volcanoes in or near the high plateaus in your story that could release poisonous gases. Poisonous volcanic gases that are heavier than other atmospheric gases might collect in lower areas and be denser there than in higher areas.

Possibly the natives live in a forest almost surrounded by lower forests with lethal concentrations of volcanic carbon dioxide which helps the plants grow very lush.

Radon is a dense gas produced by radioactive decay of uranium and thorium. It is produced by natural radioactive decay of those elements in rocks and soil and often concentrates in low spaces. Radon is more common in some areas than others due to differing geology. And breathing radon gas is the second most common cause of lung cancer.

So possibly Radon gas is more common on your planet and more common at lower altitudes, and the colonists would want to avoid going into lower altitudes without breathing equipment as much as possible.

Possibly your world could have a denser atmosphere than Earth's, even at a height of 2,500 meters, and even denser at lower altitudes. And it also has higher average proportions of various gases like argon, carbon dioxide, and radon, so that the denser atmosphere at lower levels is too toxic for humans to breath for long.

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  • $\begingroup$ It's 2500m above sea level but I think it's a cool idea $\endgroup$ – Jean-Abdel Sep 15 '18 at 18:57
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    $\begingroup$ Perhaps the first series of air quality drone probes sent into the lowlands all reported back unbreatheable conditions and no animal life forms. Unbeknownst to the scientists, the civilization below is leery of the newcomers and purposely tinkered with the probes to send back erroneous data. Then one day a young rebellious lowlander is bored and sends back a virus too. Now the scientists have lost their AI, but not before one genius figures out they were hacked and the data had been altered. He managed to get a snippet of the correct video footage JUST as all the AI crash completely... $\endgroup$ – N2ition Sep 16 '18 at 3:15
  • $\begingroup$ My civilization is somewhere between late middle age and pre industrial, and the virus came from earth. $\endgroup$ – Jean-Abdel Sep 16 '18 at 9:11
  • $\begingroup$ @Jean-Abdel I missed that, sorry. $\endgroup$ – N2ition Sep 17 '18 at 21:44
  • $\begingroup$ No I added it later $\endgroup$ – Jean-Abdel Sep 18 '18 at 15:53
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I'd suggest that the lowlands be an entirely hostile environment, if the forest is made up of something similar to, but not as nasty as, the Manchineel Tree then the colonists will stay on the high plateaus of the world and avoid the lowland forests. Until that is something worth the investment, in both time and resources, to break out, or worse yet devise, protective equipment crops up. Like the opportunity to make first contact with sentient natives. The native lifeforms would have a different body chemistry such that they rely on the human-toxic environment for their very survival so they rarely venture far enough up onto the plateaus to leave any evidence of their presence.

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Raised elevations are cooler. Assume your planet is warmer than Earth. Even on the elevated plateaus the temperatures are barely tolerable. The lowlands are too damm hot and humid. Basic comfort would induce the colonists to cooler locations.

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They just haven't gotten around to it yet.

They've been carrying out satellite and/or air surveillance, and probably brief physical visits to collect samples from as many places as possible, but there's an entire world to be mapped and sampled, as well as a base to establish, and there's only so much fifty people can do. Even if they had visited the forested area once or twice, they wouldn't necessarily have noticed anything unless they just happened to stumble across a populated area or thoroughfare.

As far as more detailed surveys of particular areas go, the forested area wasn't near the top of their list. They would have gotten to it eventually, of course, but that could easily take several years.

If it suits your story, perhaps some of the scientists have been agitating for a more thorough survey of either the forest in particular or of all the area surrounding the plateau, but the commander is a by-the-book sort of person, and by the book, areas that can't be reached by air either aren't a priority, must not be surveyed at all during this phase of colonization (because of the higher risk involved) or must not be surveyed without special equipment that isn't available yet, e.g., fully enclosed vehicles of some kind.

(They might have ordered said equipment and be waiting for it to arrive, or perhaps it's always been booked in for the 3rd provisioning drop, or perhaps they're supposed to build that sort of stuff themselves but the auto-fabrication machinery is booked solid for the next two years. Or they haven't mined enough of the necessary raw material yet, or perhaps the ores they need are rare on this planet and they haven't found enough yet. The details depend on what sort of technology you envisage them having, but there are endless possible variations on the same basic theme.)

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This is actually a difficult question to answer, since human beings are both very curious and extremely adaptable. Consider the Ancestors, with Paleolithic technology walked around the world, and didn't let small things like oceans, glaciers, other hominid species or predatory megafauna deter them in any way.

enter image description here

Guys like these walked around the world, and settled every place it was possible to support life. He would be very interested to know what's down below the plateau

We (all living humans) are their descendants, and have inherited all the qualities which made them successful, so whatever is stoping the team on the plateau from exploring will have to be very extreme. This of course complicates the story telling, since whatever is so extreme that it would prevent human exploration in the lowlands is likely to make survival in the plateau extremely difficult as well.

So in essence, the setting will have to be ramped up to the point the team on the plateau is doing a large scale retelling of "The Martian". This isn't a bad thing, incidentally. An alien civilization living in an extreme and unearthly environment is much more believable in a "hard" SF setting, and if our heroes are busy trying to stay alive, this can make an interesting variation of "First Contact", the aliens creep up the mountains to see what is causing these strange lights, sounds, electromagnetic signals. How they react when they discover the team, and how the team reacts to being contacted by the aliens could make for a fascinating story.

Good luck!

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This is a tough one: given that your colonists have come to this world specifically to scout out the possibilities for sustaining civilisation, and that they've apparently been here for several years with full space-age tech before their AI went kaput a few months ago, it's hard to see why they wouldn't explore the lowlands. Even if the atmosphere down there is toxic (I don't know enough about gases to comment on this), surely they would at least send a few scouts in biosuits, or drone missions.

However I think there is a plausible answer, based on an adaptation of what Henry Taylor said which allows you to keep your current timeframe. If the AI was indeed flawed from some time before the crash, then maybe it took a while for the corruption in the computer systems to become noticeable. Shortly after arriving, the colonists noted that conditions in the lowlands were inhospitable and decided to send unmanned robots to make a preliminary exploration of this area. These robots returned data which suggested that the lowlands were totally devoid of advanced life, and thus not worth further investigation; however, unbeknownst to the settlers, the virus was already corrupting the bots' AI and causing them to return these wildly inaccurate results. No-one realised the mistake at the time, and when the virus later got out of hand and crashed the computers outright, the settlers were too busy trying to survive the loss of all their tech to think about the implications for the earlier mission. Until now, that it...

To flesh this scenario out in more detail, you would need more info about the cause of the problem with the computers (you presumably already have an idea about this). It becomes more plausible if someone deliberately planted the bug (perhaps with the express intent of sabotaging the colonists' ability to detect life) than if it was just a random programming accident, but it could still just about work in the latter case.

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Don't forget a simple reason: "you can't get there from here". If your 2500m elevation includes 1000m of vertical (or even overhanging) cliff face, that would be quite a big deterrent for exploration.

Such a cliff isn't too implausible, in terms of geology. A gradual uplifting of the land, plus rock soft enough to form a raised beach structure, would do the job. On earth, sea levels have changed by several hundred meters over the last 500 million years.

Sure, they could use their helicopter. But reading your question literally ("helicopter", singular, not plural) would they want to risk that asset on a mission if there was no way to repair the machine or recover the crew after a breakdown?

Of course your colonists might eventually find a way down, but how many months or years are they willing to spend searching for it?

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I think temperature would be the best option for making it very difficult to explore the lowlands. Have this world be much like this one. http://www.worlddreambank.org/C/CAP.HTM The expedition sets down on a plateau at fairly low latitude where the plateau is pleasant for humans but the lowlands are lethally hot. When the computer bug strikes they have lost much of their high technology including the air conditioned vehicles that would make exploring the lowlands feasible. The intelligent natives find the highlands unpleasantly cool so they seldom go there. The natives probably fly in the high pressure lowlands so the difficulty of flying in the highlands is another disincentive for the natives visiting the highlands, thus delaying first contact. I see 2 others mentioned temperature, but I thought I would put in a more expanded version of the idea.

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The AI was overbearing. Networked tools (everything above a hammer) would actively resist being carried into dangerous terrain - the definition of dangerous being done by AI (and a small superuser-key-bearing elite). Humans felt swaddled, overprotected and manipulated (a feeling that fostered the virus attack), but could not refuse the AI, it being everywhere.

The AI may have known of the population below, but because of incomprehensible reasons felt it too dangerous to tell the humans. So they lived blissfully unaware of the valley dwellers, who in turn, were kept from the mesas by more robust AI intervention.

Missions to new planets may seem dangerous too, but a) the definition of dangerous may be rather complex and b) this form of intelligence gathering mission may be cleared by the elusive superusers.

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Simplest answer is the one that has happened numerous times.

People don't explore distant hostile environments until they have exhausted their own environs.

Humans settled the whole Earth but it wasn't a constant move of exploration, normally they would consolidate in an area, then population or other pressure would make them move further. Unless there was an overriding reason such as warfare the moves weren't very far each time, just far over time.

Your colonists would be in the early consolidation phase.

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  • $\begingroup$ They are scientists not hunter-gatherer, their job is to explore, and I don't think scientists would decide to avoid an area a few hundreds of kilometers far while they have modern vehicles unless there's a good reason. $\endgroup$ – Jean-Abdel Sep 15 '18 at 20:01
  • $\begingroup$ @Jean-Abdel Quoting the OP 'They have no incentive' so why waste fuel and go into potential danger, also hunter gatherers know how to live off the land, scientists less so. $\endgroup$ – Kilisi Sep 16 '18 at 3:45
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Put some extra oxygen in the atmosphere. (Perhaps put some other gases also so as to keep the oxygen percentage from getting too high as it's a fire risk.)

At this point the lowlands are toxic for long term exposure. It's possible to venture down there with special breathing apparatus but no unprotected human will go poking around down there for very long--and without vehicles the trip will take longer than the safe exposure limit. Hence it's a realm for the scientists only--and your survivors won't be wasting time on such science.

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The colonists are on a plateau that would be similar in environment to a Savannah for example. This provides a path of least resistance for camp setup because of stable climate , ability to scan up to horizons for incoming predators and the like , better navigability and east to erect infrastructure.

However once the colonists setup camp. They were infected with a symbiotic pathogen that disrupts the dopaminergic system. Essentially this causes a kind of laziness to set in. Although they would do enough to get over the day . Their will to explore and see out what is below has essentially been zapped. They have no intention to go beyond what they are now used to.

Similar kind of laziness has been hypothesised to have caused the death of Homo Erectus

https://www.iflscience.com/editors-blog/homo-erectus-died-out-because-they-were-too-lazy-to-adapt-to-changing-climate-study-suggests/

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