What would changing these qualities do to an earth-like world?
Would humans and other earth-like life be able to survive, and what effects would this have on them?
And what modifications would need to be made to support Earth-like life?

Mass: 1.5 (Earth = 1)
Radius: 1.25 (Earth = 1)
(gravity: 0.96)

Atmospheric Percentages
Nitrogen: 55.5%
Oxygen: 25.5%
Argon: 15%
(The rest would be more or less the same)

[IMPORTANT EDIT]: There should probably be either more nitrogen stored somewhere else in the nitrogen cycle or more phosphorus in the soil (which is more likely? and what effects would either of these have on the planet or its inhabitants?)

Atmospheric Pressure at Sea Level: 1.7atm

Atmospheric Pressure at Altitude
Pressure 0.005474674atm at Altitude 50,000m

I read another post, here, about glowing thunderstorms or lasers with more argon/neon in the atmosphere. (I could also have krypton instead of argon? I have no clue what that would do)

Answer any or all if you can! :) (Not against using magic)

  • $\begingroup$ Your first two questions are way too broad. $\endgroup$ Commented Aug 5, 2019 at 0:40
  • $\begingroup$ Hi Dave, and welcome to Worldbuilding! Here we focus on specific and reasonably-scoped questions rather than acting as a discussion forum. I'd recommend taking our tour and visiting the help center to get a better sense of what questions are answerable here. I'd also advise our Sandbox for further advice on getting good answers. I've voted to place your question on hold until you get a chance to narrow it down a little. $\endgroup$
    – Dubukay
    Commented Aug 5, 2019 at 3:27
  • $\begingroup$ Okay, I tried narrowing things down a bit. How’s that look? $\endgroup$ Commented Aug 5, 2019 at 5:12
  • $\begingroup$ It's a good edit, but we'll only be able to coherently answer a single question at a time. You've got six or so questions built into this one question that are loosely related, but might be better asked as separate questions entirely. It's not uncommon to have "threads" of questions where a particular focus is dissected one aspect at a time, and that setup may work well for you here. For example, your second question about earth-like life's viability might render your third unnecessary if the answer is "humans would do just fine on this planet". Your question about soils and thunderstorms... $\endgroup$
    – Dubukay
    Commented Aug 5, 2019 at 5:33
  • 1
    $\begingroup$ A few other Worldbuilding helpful hints: it's usually a good idea to wait at least 24 hours to accept an answer, in case an expert or particularly ingenious user is currently asleep. It looks like your question will indeed soon go on hold - don't panic! Once you edit it, it'll be automatically nominated for review for reopening. Finally, feel free to ping people with the @ symbol in comments to send them a notification when you respond; I almost missed your response! $\endgroup$
    – Dubukay
    Commented Aug 5, 2019 at 5:36

1 Answer 1


The single biggest inhibitor to life you'll find on this planet is the high oxygen count. It's a common mistake that many people make first time out of the gate to try to set the oxygen percentage the same as or close to Earth, and then dial up the pressure. But, it's not the percentage of oxygen that supports life on Earth, it's the volume. We often talk about this in terms of partial pressure.

So; the way to go about setting up your atmosphere for an alien planet is thus;

1) Add 0.16 to 0.25 ATM of Oxygen
2) Add from 0 up to 1.5 ATM of Nitrogen to taste
3) Add as much inert gases as you want, but try to keep it below around 3 or 4 ATM
4) Keep CO2, fluorine and other toxic gases to trace amounts, preferably no more than around 0.005 ATM max.

When you add up these partial pressures, you get your atmospheric pressure.

In your current configuration, you have around double the oxygen you need in your atmosphere, meaning that you could end up with long term oxygen toxicity problems for earth creatures, especially humans, which could lead to both lung and eye problems before too long.

Your planet will also be at risk of terrible firestorms as the extra oxygen will react to fire so much more effectively, making small bushfires or lightning strikes turn into conflagrations without too much trouble at all. You may on the other hand end up with large animals that don't need lungs (like insects) on your planet as a larger body could still achieve oxygen saturation through osmosis.

In reality, the single best change you could make to the planetary atmosphere, as big an irony as this sounds, to make it more habitable by humans is to dial down the atmosphere from around 0.43 ATM in your current configuration back down to around 0.2 ATM, which is around 12% of your 1.7 atmospheres of pressure.

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    $\begingroup$ Please don't answer questions that are clearly too broad or need some additional work. This makes it easier for the asker to clarify what they're looking for. Once answers are added, the question becomes much more difficult to edit without invalidating existing answers. $\endgroup$
    – Dubukay
    Commented Aug 5, 2019 at 5:37
  • $\begingroup$ Just out of curiosity, where do you get your values from? I use less then 3 atm N2, and up to 0.35 atm O2 (limit imposed by runaway wildfires which won't stop burning, thus will lower the O2 content again) for natural planets and up to 0.5 atm O2 for habitats. $\endgroup$ Commented Aug 5, 2019 at 10:32
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    $\begingroup$ @TheDyingOfLight 3 ATM of N2 is the starting point for the onset of nitrogen narcosis, and as there are no studies of the long term effects of this on people I generally halve the figure to be sure. You're right about the 0.35 ATM being the start of runaway fires, but from my diving days I also know that's getting close to the figure where oxygen toxicity could become an issue in the long term; generally 0.5 ATM is considered potentially dangerous so again I halve it as no long term studies exist. You're not wrong in your figures, mine are just designed to be conservative for long term use. $\endgroup$
    – Tim B II
    Commented Aug 5, 2019 at 23:35

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