5 comments on “World-building Part 4 – Atmospheres and Natural Cycles

  1. Pingback: World-building Part 5 – Geomorphology (planetary features) « Reshaping Reality

  2. Hello. I’ve just started a world-building project and have come across this excellent site, so first up, thanks in advance – I can see there is a wealth of knowledge here that I can draw on for inspiration. I have a tech question as a non scientist, if you don’t mind helping out a little. I don’t mind doing some research but could do with a point in the right direction. I’m looking at two terrestrial planets in a system, one very earth like, the other of similar size, still within the habitable zone but more distant from the star (fourth rock, if you like) which I have imagined as something approaching an ice-age earth, supporting a biome but with an atmosphere toxic to humans. Would ozone be the ingredient to increase? Any clues would be much appreciated, thanks.


    • Glad to hear this site is helpful! As for your question, you certainly could use ozone, because it has extremely detrimental effects to human life. You can read more about it here: http://earthobservatory.nasa.gov/Features/OzoneWeBreathe/ozone_we_breathe2.php And here: http://www.epa.gov/spdpublc/science/effects/index.html

      Since your planet is on the far end of the habitable zone, it’s definitely going to be colder due to its orbit. Is the world tectonically active? That’d be a factor in the atmospheric composition. Carbon dioxide and methane are fairly toxic to us as well, and if it is tectonically active, those may appear in some abundance. Though they also may warm the planet more than you may wish. Point is, ozone doesn’t necessarily have to be the main toxic gas. (Take a look at Titan, one of Saturn’s moons. It’s fairly cold and has methane seas (methane will condense only at a fairly low temperature)). Your fourth planet may not be sufficiently far away to have methane oceans, but it could be far enough away for dry ice — like Mars — to form on the surface. How cold does it get on your planet?

      In regards to Ozone: for it to appear in significant quantities, especially at the ground level where humans would encounter it, it would need to encounter hydrocarbons and nitrogen oxides. Add those two with sunlight, and ozone will form close to the surface. But now you need an abundance of hydrocarbons and nitrogen oxides. What produces those? For Earth, it’s our cars, factories, and plants and soil. Nitrogen oxide is formed naturally from bacteria processes, biological growth and decay, lightning strikes, and forest and grassland fires. The biggest and fastest way to form it is through combustion, which also helps form hydrocarbons. Fires and lightning are natural ways to form this, but then to have fires you need the area to be dry enough to catch on fire (due to a lightning strike is the most natural way for it to happen).

      An area can be both dry and cold and still be able to burn. So it is possible to produce both hydrocarbons and nitrogen oxide through fires on a cold planet. The other possible route is through bacteria process and biological decay.

      Ozone is depleted through chemical interactions with chlorine molecules and especially through chemicals produced in volcanic eruptions. This gives insight into how this happens: http://www.epa.gov/ozone/science/process.html

      So if you want ozone to be dominant in your atmosphere, it may help to develop a cycle for its existence, so that it stays fairly plentiful. When I say plentiful, I’m really only talking a small percentage. You don’t need a lot at ground level to make it too toxic for humans. Anyway, the purpose here is to help generate ideas for you to have an ozone cycle on your planet — where ozone could become plentiful enough to create the toxicity you want for your atmosphere.

      I hoped this helped.


  3. Aibird thank you so much, that is a fantastic help. I think the ground-level ozone through biological decay sounds like it would be the right sort of fit for my idea and I will research & develop this further – thanks also for the great links. I really appreciate you sharing your time and knowledge with me.


  4. Pingback: To stand on an alien world | Reshaping Reality


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