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69

an atmosphere that is lethal if you get a breath or two but won't burn your skin off or poison you anyway when you walk out the door without your moon suit? take our atmosphere and remove all the oxygen, replacing it with an inert gas like nitrogen. Asphyxia will ensue after a couple of breathes. Asphyxia or asphyxiation is a condition of deficient ...


53

My suggestion: 60% Xenon 20% Oxygen 15% Nitrogen 5% Carbon dioxide Why Xenon? Xenon is a noble gas. It has very few common chemical reactions, and is frequently used in situations where air is too reactive to be safe. It's safe to touch and even safe to breathe. It's also a very effective anesthetic. Present-day doctors in Europe use it because it is ...


28

Pure nitrogen is harmless -- except that it won't support life. A breath or two will do no harm, but you won't even notice you're suffocating, because the carbon dioxide will clear from your blood as if you were breathing air -- but you won't be gaining any oxygen. You'll fall over unconscious after three or four breaths, and you'll die in four minutes (...


11

Carbon monoxide is a nice easy one. Colourless, odourless, non-corrosive, lethal at concentrations above 500 (or thereabouts) parts per million. It will oxidise over time to carbon dioxide in an oxygen atmosphere, so you’ll need some biological source to keep replenishing it.


10

The kidneys will deal with high CO2 The high CO2 levels you describe would produce chronic respiratory acidosis. https://www.ncbi.nlm.nih.gov/books/NBK482430/ The primary disturbance of elevated arterial PCO2 is the decreased ratio of arterial bicarbonate to arterial PCO2, which leads to a lowering of the pH. In the presence of alveolar ...


7

Any atmosphere that contains gases that are inert to a human metabolism, but no Oxygen or not enough Oxygen. One would be an atmosphere containing 5% oxygen instead of the usual 20%, with the 15% made up of Nitrogen and Argon as here. At one atmosphere, it's equivalent to a depressurized airliner at cruising altitude. You don't notice anything wrong, but ...


5

Helium. It is very inert, and used by deep divers to replace nitrogen due to it being safer at high pressures. It can enter all your tissues without causing harm. The only side effect to breathing it is a funny voice. In an atmosphere made of pure helium, a human would die of asphyxia. That would be the only damage caused by such an environment.


4

Wait, nodoby mentionned Avatar? Pandora is exactly what you describe: survivable but deadly if you breathe. Pandora's atmosphere is a mixture of nitrogen, oxygen, carbon dioxide (>18%), xenon (>5.5%), methane, and hydrogen sulfide (>1%) and is about 20% denser than the atmosphere on Earth primarily due to the high percentage of Xenon; a heavy, colourless, ...


4

First of all, your methodology is sound. Atmospheres are about partial pressure and setting up an in-ship atmosphere of around 0.2 to 0.3 ATM of pure oxygen is reasonable and actually practical; It means that your ship doesn't have as much differential pressure to deal with against the vacuum outside, meaning it an be lighter as the walls can be a little ...


4

TL;DR As most of the other answers say, the plants on this world would likely be purple-ish, using photosynthetic pigments that operate at the same wavelengths as bacteriochlorophylls. Chlorophyll a and chlorophyll b wouldn't receive as much light in the visible part of the spectrum as they do from the Sun, meaning that green plants would be inefficient and ...


2

If you're prepared to have a good fiddle with your own DNA, then there are some species out in the world that might serve as a useful template, or at least inspiration. Crocodiles have some interesting adaptations that cause oxyhaemoglobin in their blood to give up its oxygen more readily in the presence of higher levels of biocarbonate ions in the ...


2

Oxygen You cannot breath pure O2 for long, after a few hours it will start to destroy alveoli causing lungs permanent damage. It's also very toxic for your nervous system and can cause seizures and reach convulsions and unconsciousness. In fact, oxygen poisoning is a common cause of diving accidents due to the increased pressure in the diver body and from ...


1

A few effects off the top of my head: Sky Coloration A thicker atmosphere favors higher frequencies of the sky at midday and lower frequencies at sunset due to Rayleigh scattering. If your planet orbits a boring old G-type main-sequence star like our sun, its sky will likely be a dim violet, as the dominant frequency should be somewhere in the ultraviolet, ...


1

According to Wikipedia, increasing atmospheric density would increase the index of refraction for the atmosphere, causing astronomical objects, such as the sun and moon, to appear higher in the sky. This would cause the sun and moon to appear to rise earlier and set later than they actually do. One other effect is magnification of astronomical objects. ...


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