# What would happen if the oxygen and nitrogen levels were slightly different?

I was wondering if it were possible for human life to survive with slightly more oxygen and slightly less nitrogen. I know a user called @Lars asked a similar question, but it didn't give a clear answer to mine.

So, on Earth, the atmosphere is about 78% nitrogen, 21% oxygen and 1% other stuff. But what would happen if there was a planet where oxygen was around 30% of the atmosphere, and nitrogen was around 69%?

Would humans, animals and plants still be able to survive with the same techniques and adaptations, or would we have to develop new ones? Would a relatively small change (compared to @Lars's) affect life as we know it?

• "Would humans, animals and plants still be able to survive?" since earth has been in a similar arrangement in the past and life flourished i would say yes – Topcode Mar 11 at 21:11
• Hi @Delta Diamante, welcome to Worldbuilding! Let me mention the common practice here is to wait at least 24 hours before accepting an answer. People all over the world should be given a chance to read your question and answer it. – Alexander Mar 11 at 21:31
• @Alexander I am new to worldbuilding and didn't know that, thank you. – Delta Diamante Mar 11 at 21:48
• Bigger insects, bigger fires, bigger stinks, shorter lives.Nothing dear old Earth hasn't done before. – PcMan Mar 11 at 22:29
• How about the total pressure? The oxygen may be still 30% but the total pressure may vary a lot. For humans, it is the partial pressure of the oxygen that matters. – fraxinus Mar 12 at 7:27

Humans will be just fine in 30% oxygen atmosphere. The first negative health effects are believed to be happening when the concentration goes over 30% (or more precisely, oxygen partial pressure goes over 0.3 bar): Oxygen toxicity

Most animal and plant life would also be Ok - however, I can't speak for every specie.

However, higher oxygen level would have distinct effect on the environment.

1. Everything will be oxidizing (and spoiling) faster;
2. Wildfires (and human-related fires) would start more easily and will be harder to stop;
3. Insects (and arthropods in general) would benefit from higher oxygen levels disproportionately. Prepare to see some 40 cm long cockroaches crawling around.

For the nitrogen, its decreased levels would cause a small reduction in plants' ability to capture it - but this will be only a small decrease which should not have strong effect on the environment.

• On the plus side, 40 cm long cockroaches will not be able to hide under the carpet in the bathroom or in the kitchen – L.Dutch Mar 12 at 5:37
• An increased number of wildfires due to elevated oxygen levels will increase the rate of eg. $NO_2$ formation, which is a much more readily bioavailable form of nitrogen than plain old $N_2$. – Starfish Prime Mar 12 at 10:29
• It is the humans who will hide under the cockroaches carpet/bathroom – Alex bries Mar 12 at 16:27

A 30% oxygen atmosphere is a hellish place to live. That's because the only thing keeping insects and arachnics from growing bigger is the law of square cubes, their respiratory tracts can't handle the growth... Unless there is more oxygen available in the air, which is exactly what happened 300 million years ago.

Insects don't have bones, but sometimes they leave impressions on soil, and those impressions become fossils. One such insect from 300 million years ago was the Meganeura dragonfly. Its wingspan could reach up to 70cm, or 28".

Imagine living in a world where roaches are two feet long. That is nightmare fuel. Human life would never develop because our ancestors would all die of heart attack (just kidding).

That same oxygen rich atmosphere lasted during ages. If I recall correctly the dinosaurs evolved in such an atmosphere. So I don't see why current fauna and flora wouldn't be able to cope with it. One interesting thing we might see is smaller species evolving into larger forms in a very quick span of time in some places.

Oh, and forest fires. Lots of them. Such increases in the amount of oxygen in the air would cause any fire to be much more impressive. Everything burning in this atmosphere will burn faster and more intensely.

• Hellish? Are you kidding? Think about the new kinds of food available! Beetle larva steaks! Who needs to mess about fishing for lobsters when huge tasty arthropods are just running and flying around your neighbourhood, all uncooked and nutritious? Also, three words to strike fear into the heart of any burglar: Giant Guard Centipede. – Starfish Prime Mar 12 at 10:33