<p>The (dry) air in Earth's atmosphere is about 78.08 percent nitrogen, 20.95 percent oxygen, and 0.93 percent Ar. Roughly, 78% N2, 21% O2 and 1% Ar.
CO2 is a mere 0.04%.
If the oxygen content were 1.1-1.2%, we couldn't survive!</p>

CC BY-SA 4.0
2024-05-16T13:58:19.630Z
2024-05-16T13:58:19.630Z
Riccardo
<p>As a follow on to Riccardo's answer, dry-air oxygen levels are fairly stable at 20.95% outdoors. The info below is based on OSHA <a href="https://www.osha.gov/laws-regs/standardinterpretations/2007-04-02-0" rel="nofollow noreferrer">here</a> and <a href="https://www.osha.gov/sites/default/files/2018-12/fy15_sh-27664-sh5_Confined_Space_Handout_Effects_of_Oxygen.pdf" rel="nofollow noreferrer">here</a>:</p>
<ul>
<li><p>Below 19.5% - air is oxygen deficient and one should leave the area</p>
</li>
<li><p>16%–19.5% - decreased ability to work and for tissues to receive oxygen they need, impaired thinking while not at rest</p>
</li>
<li><p>12%–16% - increased breathing rates, increased heartbeat, impaired thinking at rest</p>
</li>
<li><p>10%–14% - faulty judgement, intermittent respiration</p>
</li>
<li><p>6%–10% - nausea, vomiting, lethargy, loss of consciousness. Fatal in about 8 minutes</p>
</li>
<li><p>0%-6% - convulsions, cardiac standstill, fatal in about 40 seconds</p>
</li>
</ul>
<p>When you are exposed to oxygen poor air a body can rapidly release oxygen it has based on  Le Chatelier's principle. Which is why death can occur much quicker than humans can hold their breath.</p>

CC BY-SA 4.0
2024-05-17T22:03:22.777Z
2024-05-17T22:03:22.777Z
unstar782
<p>I recall (although, perhaps wrongly), from my PADI scuba diving books, that air is made up of 78% nitrogen, 0.8% CO2 and 1.2% O2.</p>
<p>I was wondering, what would happen to our lungs (or to that of any other living creature on Earth), if, that proportion changed.</p>
<p>For instance,</p>
<p>consider</p>
<p>78% nitrogen, 0.9% CO2 and 1.1% O2.</p>
<p>I was wondering, hopefully, my question is a good one (I don't know if it's good or bad), but thank you for your answers, I think this would be intuitive, and shed light, on the workings and life of many living organisms.</p>
<p>Thanks.</p>

CC BY-SA 4.0
2024-05-21T22:27:37.883Z
The quoted numbers are incorrect; 1.2% O2 is way too low, should be ~20% and CO2 is way too high, should be ~0.04%. Nitrogen is about right. Check the source, try some others. Usually gas proportions are for dry air and leave out water vapor, that varies widely.
Ken Fabian
<atmosphere><atmosphere-modelling><upper-atmosphere><air>
Effect of changes in the air's nitrogen-oxygen-carbondioxide proportions
Joselin Jocklingson
# Effect of changes in the air's nitrogen-oxygen-carbondioxide proportions

(Asked by: username_0 on 2024-05-16)

I recall (although, perhaps wrongly), from my PADI scuba diving books, that air is made up of 78% nitrogen, 0.8% CO2 and 1.2% O2.

I was wondering, what would happen to our lungs (or to that of any other living creature on Earth), if, that proportion changed.

For instance,

consider

78% nitrogen, 0.9% CO2 and 1.1% O2.

I was wondering, hopefully, my question is a good one (I don't know if it's good or bad), but thank you for your answers, I think this would be intuitive, and shed light, on the workings and life of many living organisms.

Thanks.

**Tags:** atmosphere, atmosphere-modelling, upper-atmosphere, air

> **Comments:**
> **username_1**: The quoted numbers are incorrect; 1.2% O2 is way too low, should be ~20% and CO2 is way too high, should be ~0.04%. Nitrogen is about right. Check the source, try some others. Usually gas proportions are for dry air and leave out water vapor, that varies widely.  

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## 2 answers

### Answer by username_2 on 2024-05-16. Score: 3

The (dry) air in Earth's atmosphere is about 78.08 percent nitrogen, 20.95 percent oxygen, and 0.93 percent Ar. Roughly, 78% N2, 21% O2 and 1% Ar.
CO2 is a mere 0.04%.
If the oxygen content were 1.1-1.2%, we couldn't survive!


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### Answer by username_3 on 2024-05-17. Score: 2

As a follow on to username_2's answer, dry-air oxygen levels are fairly stable at 20.95% outdoors. The info below is based on OSHA [here](https://www.osha.gov/laws-regs/standardinterpretations/2007-04-02-0) and [here](https://www.osha.gov/sites/default/files/2018-12/fy15_sh-27664-sh5_Confined_Space_Handout_Effects_of_Oxygen.pdf):

* Below 19.5% - air is oxygen deficient and one should leave the area
* 16%–19.5% - decreased ability to work and for tissues to receive oxygen they need, impaired thinking while not at rest
* 12%–16% - increased breathing rates, increased heartbeat, impaired thinking at rest
* 10%–14% - faulty judgement, intermittent respiration
* 6%–10% - nausea, vomiting, lethargy, loss of consciousness. Fatal in about 8 minutes
* 0%-6% - convulsions, cardiac standstill, fatal in about 40 seconds

When you are exposed to oxygen poor air a body can rapidly release oxygen it has based on  Le Chatelier's principle. Which is why death can occur much quicker than humans can hold their breath.


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