Spicing Up Your World’s Chemical Makeup

One of many great landscapes by FPesantez (Deviant Art member)

Strange skies and spires Fantasy v03 by FPesantez (formerly doppingqnk) used under CC BY-ND 3.0

This post is 2 in the series: Setting Your World Apart From Earth

Are you cooking up a world for your story or game, and Earth-standard is just a little too bland? Want to give your setting a subtly different flavor without overwhelming your story, or adding a bad fridge-logic aftertaste? Well then, we have the perfect blog series for you!  (Hint: it’s this one. The one you’re reading right now.)

We’ve already discussed how to give your sky a science-informed makeover. If you just plop suns and moons into your sky at random, your world and your characters are likely to experience curious radiation, strange tides, and other decidedly non-Earthlike consequences. As we focus our attention downward to the air, water, and soil, the same theme applies: add the wrong spice, and your dish won’t have the taste you’re hoping for. But don’t worry, here are some basic recipes to prevent a kitchen disaster.

The Aerial Soup

This cloud could consist primarily of water droplets... or maybe toxic phosgene?  You won't know until you try breathing it!  Mwahahaha! This cloud could consist primarily of water droplets… or maybe toxic phosgene? You won’t know until you try breathing it! Mwahahaha! Alien Cloud (Stock 002) by AlzirrSwanheartStock (Deviant Art member name) used under CC BY-ND 3.0

The soup of gases your characters will be breathing – their planet’s atmosphere – represents a huge source of potential variation. Worlds can become curiously alien (and deadly for humans) with a few invisible adjustments to gas ratios. But you don’t even need to think about your atmosphere’s specific mix of chemicals to whip up something strange. Just take Earth’s ready-made soup-blend, and only add half the packet.

As any hardcore mountain climber can tell you, thin air does more than make breathing difficult. On a world (or mountaintop) with a low-pressure atmosphere, expect less flight, quieter sounds, weaker wind, and skies that stay dark and starry, even after dawn.* Extreme temperatures will be more common, but also less dangerous. Atmospheres help insulate against large swings between day-side and night-side temperatures, so a world with thinner air will have more dramatic temperature swings.* However, the same temperatures are not nearly as dangerous with thin air.*

Curiously, cooking becomes more difficult, because water can boil at surprisingly low temperatures if the air is thin enough. If the boiling point drops too low, liquid water can never get hot enough to properly cook a meal; pressure cookers and steam cookers would be essential chef tools.

If the thin air is oxygen with just a dash of other gases, your characters could still breathe easily (and fires would be just as powerful) despite the other low-pressure curiosities.*

Add two or more packets of pre-mixed Earth air to achieve roughly the opposite effects. Heat and cold are more dangerous, wind (even slow wind) is knock-you-on-your-butt powerful, and flight is a breeze. Combined with lower gravity, humans could fly (awkwardly) by strapping cardboard to their limbs and flailing. Your characters will feel invigorated, assuming there’s proportionally the same amount of oxygen in the air. But extra oxygen is a mixed blessing: too much can have long-term toxic effects, and fires turn manic.

Need more flavor? For simple tweaks to the atmospheric recipe, keep the oxygen roughly constant* and swap out the “filler” gas (nitrogen, in Earth’s case) for something more exotic. Most organisms don’t use the nitrogen in the air for anything; the exception is nitrogen-fixing plants and bacteria, which are essential parts of the food chain and nitrogen cycle. Life could still flourish, but bioavailable nitrogen sources would be a major limiting factor, and any locally-evolved life would likely have different, nitrogen-efficient biochemistry.*

If your characters are on a low-nitrogen diet, you can try these alternatives – each with their own funny aftertaste:

  • If your inert gas is sulfur hexafluoride or some other highly potent greenhouse gas, your world could stay steamy-warm despite a dim, distant sun.
  • If the inert gas is a liquid at low temperatures, your soup might have multiple creamy layers. That is, your world’s sky would have both water clouds and, say, propane clouds. Well, except they would burn.  Dichloromethane or freon would be good non-flammable choices, if it weren’t for all the ozone depletion, cancer, and other forms of toxicity your characters would have. Finding non-toxic, non-flammable gases with the right range of properties is hard; in a pinch, you can always make your locally-evolved life immune to the local spices.
  • If you want to keep the world cool despite a looming fireball of a sun, try gases which can form high-altitude hazes that reverse the greenhouse effect. All sorts of ingredients can be used here, since these gases are effectively garnish; few characters are going to be eating (er, breathing) the gases you use to decorate the stratosphere. A great Earth example is ozone: when it’s found at ground level it’s a noxious, toxic pollutant. But hanging 15 miles above our heads, it’s a convenient little umbrella for those of us who don’t want to live like vampires.
  • If the inert gas is heavy xenon, it could become super-concentrated in low crevices, mines, and seas – displacing oxygen and causing all sorts of curious problems to those exploring the deep places of your world.*  Low winds make this even worse. Dense, murky layers tend to form when you don’t stir your soup and it’s full of heavy stuff.
  • Perhaps your inert gas isn’t so inert when applied to human biology.  Dumping in the whole bottle of carbon dioxide (an essential spice, in small amounts) would yield a rich, green world that’s hostile to non-adapted outworlders.*

Atmospheres have an important effect besides keeping temperatures mild and giving us something to breathe: liquids of any sort cannot exist without a layer of gas pressing down on them. It has to be reasonably thick – though just a few percent of Earth’s will do, so long as the planet is fairly cold. Mars, for example, can support (just barely) a bit of liquid water in its deep Hellas Basin, where the air pressure is ~1% that of Earth’s at sea level. For purposes of keeping water liquid, it doesn’t matter what the gas is, just so long as there’s enough of it. So if your world doesn’t have much air, it probably doesn’t have much water either.

The Deep Blue Soup

It's weird!  It's alien!  It's... okay actually this is just off the coast of Belize, in the Caribbean.  It's called the Great Blue Hole. It’s weird! It’s alien! It’s… okay actually this is just off the coast of Belize, in the Caribbean. It’s called the Great Blue Hole. Image by USGS

Speaking of water, if your planet’s going to be remotely Earth-like, or human-habitable at least, it should have an ocean or two.* Even desert planets need SOME permanent sources of water, somewhere: a few large lakes, an underground sea, or a canal fed by an icecap. However, these H2O reservoirs don’t have to be very big. We could easily get by with one percent or less of the total water on Earth so long as it remained spread out over a large area. The surface area of the oceans is what really matters.* A desert world with some water would still have greater temperature variation, less rain overall (except downwind from the coast, depending on latitude), fewer hurricanes and thunderstorms (hurricanes require open water; thunderstorms require high humidity), more sandstorms, and other common-sense implications of a drier locale.

The impact of terrain means that an ocean world isn’t quite the polar opposite of a desert world – especially a mountainous desert world. On a planet where the only landmasses are scattered archipelagos or isolated subcontinents, ocean currents and air masses zoom around unhindered. The weather behaves like the southern hemisphere of Earth: moist, mild maritime climates predominate, and hurricanes have free reign.

A Closer Look: Hurricanes

These powerful heat engines depend on three things: how much water is around, how hot it gets, and how fast the planet is rotating. A hot, rapidly rotating waterworld is going to be hurricane central. Perhaps not as ridiculous as a tidally-locked world with its permanent sun-side hurricanes, but dangerously hurricane-infested nonetheless. Crank up the surface water temperature to 50°C or above, and your world is ready to spawn some civilization-erasing hypercanes.*

Alien ocean chemistry will make your world seem more exotic, but there are limitations to what you can brew up while retaining human habitability. As human-friendly atmospheres need oxygen, human-friendly oceans need water. Oceans on habitable planets can be acidic, basic, alkaline, heavily salted, fresh, anoxic,* or toxic. Heck, juice, blood, or stew are fine,* but oil, hydrocarbons,* and mercury are not. There are worlds that contain exotic non-water seas (for example, the great hydrocarbon lakes of Titan) but humans will almost certainly be limited to dome cities on these worlds.*


As a case study, let’s look at the hypothetical world of Vampyria, a planet terraformed by vampires to have oceans of blood.* Could the vampires settle human colonies here, in case they feel like hunting something? No problem. Humans and animals couldn’t drink the blood of the oceans – but neither can they drink the salty water in Earth’s oceans without dehydrating. Humans and their agriculture would be supported by rainfall, rivers, and lakes – all of which would be fresh, non-bloody water. Water evaporating out of the blood oceans would be just that: water. The oceans might be a bit ridiculous, but the rest of the world doesn’t have to be.

The Soup Crackers

Spiky land-crackers Spiky land-crackers! Fantasy Landscape: Mountains by FPesantez used under CC BY-ND 3.0

Is your world porous? Do the tallest mountains stretch into space? Are there miles-deep gashes and rifts? Exotic terrain can be more than planetary window-dressing. It can alter how the atmosphere and biosphere function, and provide exotic niches for strange life forms to adapt to.

Deep airspaces will be the most interesting of these exotic places, as they’re guaranteed to be unlike anything on Earth: pressure-cooked jungles where UV is negligible* and damn near everything can fly. Or, if the world is a Mars-like wasteland of dry, airless plateaus, these deep places will serve as vital oases of life, perhaps the only places on the surface where humans could live. However, if winds are slight, an atmosphere’s heavier gases may settle semi-permanently in deep spaces (such as in vast caverns of a porous world). Oxygen isn’t typically included on the “heavy” list, so this is a problem for humans – and that’s before considering how toxic these gases can be.*

Spacescraping mountains are a little less interesting (cold, barren, deadly), but things get better when the planet’s air is so thick* that the mountains are the only human-habitable areas. They would become like islands separated by seas of air; your inhabitants had better be able to fly!

In addition to the obvious air-pressure changes, high-relief terrain such as very tall mountains, ridges, spires, and criss-crossed canyons will wreak havoc on your weather patterns and climate zones. This isn’t un-Earth-like per se; our planet has plenty of rain shadows, cold “tropical” highlands (e.g., the Altiplano), and peaks so massive they generate their own weather. But this can all be scaled waaaay up, especially if your gravity is low. Your world’s jet streams and other regular patterns of air circulation could be driven completely batty with enough vertical relief. This is arbitrary enough that hand-waving (the lazy worldbuilder’s best friend) works surprisingly well here. Why is the weather in this kingdom so strange? Probably all those impassable mountains.

Cracker Chemistry

What happens when we bake the crust of our world with different ingredients? Well, unlike the sky and sea, we have a near-infinite variety of non-lethal options. Indeed, our own planet’s crust boasts remarkable chemical diversity. That’s not to say that we can be sloppy; there are still some guidelines to consider.

First, if it’s in your terrain, that means it’s resistant to water and oxygen:

  • Anything that can dissolve in water (salts, and the like) will have ran away to your oceans long ago – unless they’re trapped in a high desert or an endorheic basin.
  • Anything flammable* will have burned already – with the notable exception of stuff that was or is alive. If it weren’t for ancient dinosaurs and ferns, us Earth-dwellers would have very little to burn.
  • Anything else that can oxidize will probably have oxidized already.  For example, there’s a lot of iron ore (essentially rust) on the surface of our planet, but not a lot of raw, metallic iron. This applies to most metals – with the notable exceptions of lead, coinage metals (copper, silver, gold) and platinum-group metals.

However, if you can keep parts of your world away from water and oxygen, those regions (likely caves) could boast some very interesting, beautiful, flammable rocks and crystals.

But remember that any Earth-like, non-desert region will have a large water table. That is, there’s always a lot of water underground. This is true even for many deserts. There’s still more water if you count the H2O molecules that are chemically bound to rocks: molecules which are released at high temperatures. There’s technically more water in our planet’s rocks than in all of its lakes.*

If you want to alter the amount of liquid or rock on your world, you can do more than just add or remove H2O. Instead, consider your planet’s temperature. Water starts behaving a bit like rock at antarctic temperatures. At very high temperatures, some rocks start behaving a bit like water.*

Last, remember that the layer of Earth that non-desert-dwellers are most accustomed to interacting with, soil, is thoroughly organic and a product of millions of years of life. That means poisonous chemicals shouldn’t be in the soil, or the soil wouldn’t have formed in the first place. And yet, this happens occasionally on Earth when soils become poisoned, or life-spurning minerals become exposed on the surface, and remain barren for ages. Gros Morne National Park in Newfoundland is an interesting example of the latter case.

There are more detailed considerations of course; geology is exceptionally tricky. Skies and oceans are always mixing, and their ingredients are fairly simple. But the rocks you might find in a single square mile all have bizarre and complex recipes with directions like “let sit on ocean bottom for two million years,” or “etch with alkali then tumble in a river for seven centuries,” or “freeze and reheat in planetary mantle twelve times,” or – my favorite – “this product is not available in your region and must be ordered from space.”


Speaking of space, we’ll be heading back there one lunar cycle from now, for the third and final post of this series. We’re going to need a zoomed-out view of our planet as we watch it wobble, spin, and gyrate in curious, civilization-altering ways.

P.S. Our bills are paid by our wonderful patrons. Could you chip in?



  1. Giana

    Thank you for this, there are things I never thought I would need for worldbuilding!

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