So me and my buddy are currently working on a story that takes place on a different earth-like planet similar to when carboniferous life like the Meganeura dragonfly inhabit the landscape. A few differences is that the 'Humans' that evolved on this planet to unaffected by the high oxygen in the atmosphere. (33% of atmosphere to be specific). The era we're worldbuilding takes place in there medieval era.

When I was doing some research on the different iron alloys. I've read that metals like iron would naturally degrade into rust over time due to binding of oxygen in the air. Natural elements like Water & especially salt water would degrade iron much more quickly. I did some research on things like Rust-resistant alloys & Galvanization. But The only problem with those 2 is these were modern methods that likely required the discovery of electricity to make these alloys.

Question: Would an atmosphere with 33% oxygen significantly alter our world's historical uses of iron for tools, structures, armor and weapons?

  • $\begingroup$ I've read that metals like iron would naturally degrade into rust over time due to binding of oxygen in the air that is true, even in our "low-oxygen" atmosphere. that's why metal-tools need to be maintained. a thin layer of oil, for example, is quite common for anything with a cutting edge. also: i doubt whether 33% of oxygen significantly increase rust compared with our 21%, so you probably can just apply exactly the same methods that mankind of earth used, without worrying too much. $\endgroup$ Commented Dec 20, 2021 at 9:20
  • $\begingroup$ The increased oxygen content would greatly increase the chance of fire. The US definition for oxygen enriched environment is 23% where there is increased risk of ignition and fire. Normal atmosphere is about 21%. So you might want more stone buildings and be more cautious in some ways. $\endgroup$
    – UVphoton
    Commented Dec 20, 2021 at 14:01
  • $\begingroup$ note oxygen levels were not higher during the time of brachiosaurus. If anything oxygen levels were similar to today, possibly even lower. so you may be doing this for nothing. $\endgroup$
    – John
    Commented Dec 20, 2021 at 22:46

2 Answers 2


Not much effect at all.

The effects would be negligible, if anything forging might be slightly easier since fuel will burn with more heat and speed. In a medieval setting low oxygen for steel making is achieve via sealed crucibles, which will work regardless of oxygen levels so the metal is not subjected to higher oxygen when it matters. Rust is not an issue solid iron does not rust noticeable faster in slightly higher oxygen, things like humidity, salt, and PH matter far more. Handling will matter, but it does for all iron tools, Oil, wax, resin, enamel, even paint will see lots of use. Consider iron tools were commonly used on ship, and salt water is a far stronger affect on corrosion than slight changes in oxygen levels.


I'm not sure my answer will be the most help, but I was curious so I looked into this somewhat.

This link is for a publication that seems to be behind a paywall, but the single page shown covers generally exactly this topic, but primarily in highly oxygenated water. The gist seems to be that rapid oxidation in water causes steel to turn into a sort of rusty gelatin, but it would be only on the outer layers of steel and corrode further in over time. Might be worth reading the whole paper if you want greater details though.

Another article I found goes a bit too over my head after a while, but seems to indicate that under high pressure iron-oxide (rust) keeps its ferrous state, although non-magnetically. I didn't see where it indicated at exactly what pressures other than deep in the Earth's crust, but the atmosphere could possibly have a high pressure as well. There is also quite a bit relating it to iron-sulfide (pyrite/fools gold). Like I said though, fifteen minutes of reading ended up going much further over my head than CHEM 201.

I would recommend trying to getting clarification from someone much more versed in metallurgy, geology, and/or chemistry. I would suggest considering the greater affects of higher oxygen on other aspects of the world such as water oxygenation and how that affects climate and other natural reactions. Fire would be a much bigger deal in this world as it would be much easier to start one and it would get much larger faster. Obviously we have archeological references for flora and fauna, and you seem to have hand-waved human biology too. You may want to just hand-wave a lot of the more tedious details as well.


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