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Question

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. They are 50 and have buggies, guns and an helicopter but a few months before the evidence of alien civilization all the AI in these are destroyed by a computer virus so 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. Basically they have advanced technology but no incentive to go to the lowlands, then later they have only basic technology but strong incentives.

You just might be interested in my question What can I add to an oxygen/nitrogen atmosphere to make it unpalatable or poisonous to humans, yet stable and breathable to local creatures? — 3 hours ago

Henry Taylor 41.8k764150 · Answer 1 · 2018-09-15 15:09:09Z

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.

"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. — 2 hours ago
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. — 1 hour ago

score 1 · Answer 2 · 2018-09-15 17:16:22Z

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.

M. A. Golding 6,295421 · Answer 3 · 2018-09-15 17:49:30Z

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.

It's 2500m above sea level but I think it's a cool idea
â€“Â Jean-Abdel
9 mins ago — 9 mins ago

Willk 87k22171375 · Answer 4 · 2018-09-15 15:08:09Z

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 CoffinÃ¢Â€Â™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.

Kilisi 11.2k12055 · Answer 5 · 2018-09-15 15:20:37Z

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.

CWallach 892 · Answer 6 · 2018-09-15 17:27:24Z

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.

Henry Taylor 41.8k764150 · Answer 7 · 2018-09-15 15:09:09Z

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.

"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. — 2 hours ago
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. — 1 hour ago

score 1 · Answer 8 · 2018-09-15 17:16:22Z

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.

M. A. Golding 6,295421 · Answer 9 · 2018-09-15 17:49:30Z