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Is it possible for humans to live on a world with the following conditions?

Atmosphere:

  • 50% nitrogen;
  • 30% oxygen;
  • 20% carbon dioxide.

Climate:

  • The rain in some areas is acidic. (Is there some factor other than air currents that affects the creation of polluted clouds and its rainfall?)
  • Temperatures between -5 ° C and 30 ° C.

Flora:

  • Some more robust plants than Earth survive the acidic waters and produce oxygen, along with some seaweed caves with pure water.
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  • $\begingroup$ What kind of atmospheric pressure is present? $\endgroup$ – March Ho Dec 28 '14 at 9:07
  • $\begingroup$ similar to ours (if that is possible) $\endgroup$ – ballah Dec 28 '14 at 15:34
  • $\begingroup$ You need at least some H20, or the answer is invariably no. $\endgroup$ – Xandar The Zenon Jan 22 '16 at 23:42
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Assuming atmospheric pressure is similar to Earth sea level, the number that immediately jumps out is 20% carbon dioxide. This is far above levels in Earth's atmosphere.

According to the wikipedia page, symptoms of hypercapnia include diminished vision, shortness of breath, sweating and unconsciousness at 8% CO2 in the air. (Earlier symptoms include drowsiness, headache, confusion, increased heart rate, etc.)

Other than that, the percentage of oxygen is within the range of what existed in Earth's atmosphere during the Carboniferous period, so I doubt that would be a problem. Temperatures are within the range found on Earth. And you mention that pure water is available.

So if humans live on this world, I think their first concern (by far) would be scrubbing CO2 out of the air they breathe, and their next concern would be whether the "robust plants" that tolerate acidic conditions are edible.

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CO2 is way too high. Possible effects:

  • Change of PH (acidification) of blood. BAD for all of the body chemistry.

  • Replacing oxyhemoglobin with carbaminohemoglobin. Reduced transport of oxygen by the blood, even with the increase of the oxygen % in the atmosphera.

  • Levels of CO2 in blood is what causes the "reflex to breathe" (the urge that you have to breathe when you are suffering Apnea). Chainging the base level from 0.03% in Earth's atmosphera to 20% would be unworkable. http://en.wikipedia.org/wiki/Apnea#Complications

  • Apart from that, the rise in the level of oxygen is also not good (remember, pure oxygen is toxic), but pales in comparation with the issues due to CO2.

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Mmm, in a 30% oxygen environment, human hair and some fatty human tissues would burn like a paraffin torch at the smallest spark.

Not that you would much care at that point. The 20% CO2 (=200,000 ppm) would have you unconscious and dying in minutes.

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Funny thing, most of the rest of the universe is far, far more hostile to humans than the environment you describe. So, with gas masks glued to their faces (and absolutely no smoking) they might survive for a while, especially if they can build (fireproof) controlled environments where they can, for instance, safely take off the masks to eat, drink and complain about being sent there.

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Yes, absolutely.

In fact, assuming Earth-like atmospheric pressure, that is a relatively welcoming environment compared to most of the rest of the universe. We would be very lucky if Mars had such an atmosphere. Humans will, though, need some sort of breathing apparatus when outside as (has been pointed out) the amount of CO2 you describe would be toxic, and appropriate shelter depending on what you mean by 'some rain is acidic'. But otherwise the temperature range is quite pleasant, having O2 in the atmosphere is good (might actually be a bit high, but irrelevant since you can't breath the atmosphere directly anyways), and even the CO2 might be conducive to plant growth.

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Another problem (beyond already mentioned way too high CO2 - which would also cause greenhouse effect and baked the planet, a MAJOR problem) is low N2 (minor problem). Many plants use N2 from atmosphere, it would be harder to do that.

Ocean would be more acidic and food chain would be very different - most small animals would not be able to build shell in such acidic water. Ocean would be ruled by jellyfish and algae.

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