The trope here is a world with 3-4 X earth atmosphere with high oxygen content (30%). Nice things about this are it enables heavy beasts to fly, and the high pressure smoothes out the negative effects of long nights and inconsistent illumination.

Downsides are low bio diversity since the atmosphere ensures that most biomes are at similar temperature and humidity, and regular flash fires caused by lightning combined with high 02 causing the burning down of large swathes of biomass.

Mountain ranges may offer lower pressure biomes but they are not the rule. The local non sentient fauna, and flora has presumably adapted to these conditions.

How might a species which is on the verge of sapience progress to establish a robust tool-using society and later, urban civilisation, on this undifferentiated, fire-prone jungle world?

  • $\begingroup$ What do you mean by "3-4 X earth atmosphere"? $\endgroup$
    – HDE 226868
    Commented Aug 27, 2015 at 21:15
  • 2
    $\begingroup$ What parts of this do you have reason to believe will force a development materially different from how we evolved? Is it just the tendencies of fire due to the oxygen, or do you feel the other details should have an effect on the progression of sapience? $\endgroup$
    – Cort Ammon
    Commented Aug 27, 2015 at 21:30
  • 1
    $\begingroup$ The atmospheric pressure at sea level is 3 or 4 times what we experience on earth. $\endgroup$
    – rumguff
    Commented Aug 27, 2015 at 21:34
  • $\begingroup$ Wildfires are part of the ecological cycle. In Colorado the fires clear space needed for grazing for the elk and sheep. Deer will eat bushes and tree buds, but elk eat only ground growth. Wildfres are spread by winds, but can be blocked by a change of wind direction, a granite canyon, etc. Even in a high oxygen atmosphere, a wet year will mean the vegetation can resist fire easily. $\endgroup$ Commented Aug 27, 2015 at 21:37
  • $\begingroup$ The main differences with earth are that our relatively low pressure atmosphere means relatively inefficient heat transport so we have cold poles and warm equator, and more chaotic weather, so many more different biomes. So we have enjoyed greater bio-diversity as a result, versus what I imagine to be a globe spanning undifferentiated rainforest. Given that large swathes of that forest regularly burn down, how could a sedentary civilisation develop which can learn farming and tool use etc if their investments are difficult to protect from natural disaster? $\endgroup$
    – rumguff
    Commented Aug 27, 2015 at 21:37

4 Answers 4


While it seems unlikely to me that a world so different from our own would support life, let alone multicellular sentience, let alone advanced technology, we can assume it does.


First of all, it looks to me like they solved the biodiversity problem. If there is constantly fire, then this world could have biomes based solely on ecological succession. Perennial plants, carried by the winds, could be brought to a fire's aftermath and bring new life. They in turn could support larger plants, which support different animal life.

It would be difficult to farm regardless of fire sheerly because of the forest itself. While it is easy for even primitive peoples to construct fireproof barriers given the right natural material, it would be near-impossible to remove the jungle to plant a field. Rather, I picture advanced societies that focus on livestock rather than crops. Carnivores can easily become sapient; in fact, if you totally refuse empiricism, carnivores are more likely to than omnivores. Carnivores MUST outwit their prey, while omnivores get more plant matter than meat because hunts are rarely successful. That itself means carnivores have even more calories to fuel a big brain. Who cares about evidence?


First of all, biodiversity is not a problem. Remember that most of Earth's ecosystems are aquatic, and oceans must also exist on this world. Also, this world creates the possibility of air ecosystems. It is possible for nutrients to be carried by airflow or produced in the sky, allowing many and diverse lifeforms to inhabit it. This would of course be based on autotrophic aeroplankton. Now to the implication. While heavy fliers seems like a great concept, remember that weight is not the sole issue facing a larger beast. Bigger animals need more food, which means that there must be an extensive air ecosystem would probably be necessary. Even so, large animals are less active, which means these animals would probably be more like balloons than birds. They would likely at some point be exploited by said civilization as a form of transport or food and other resources (whalers would need to strike the non-buoyant portions to avoid the whole thing exploding). They would influence technology and culture; indeed, whaling may not happen simply because the animals are worshiped as gods or thought to be sacred in some way or other. Better yet, it is illegal but still done, a source of conflict in the story.

Long Nights And Inconsistent Illumination

How is this solved in a denser atmosphere planet? How is it even bad? This makes no sense to me, but I cannot comment and thus cannot ask some other way.


How might a species which is on the verge of sapience progress to establish a robust tool-using society and later, urban civilisation, on this undifferentiated, fire-prone jungle world?

Stage 1. Cave Dwellers.

The intelligent creatures learn to stay away from jungles and start residing in caves. The basic reason for this is to avoid the deadly flying predators which come out of nowhere and make a swift kill of them. The second reason is to avoid forest fires which spread to vast areas very quickly.

Stage 2. Social People

Living in caves necessitates depending on one another for safety against predators. It also necessitates that the creatures learn to trust each other. Back in the jungle life, it was everybody to himself. Now it's a teamwork.

Stage 3. Stone Craftsmen

The intelligent creatures undergo a rapid evolution focussing on the shape of their arms and hands. Living in caves for a long time, now these creatures learn to throw rocks at predators! A prolonged repetition of this activity gradually initiates an evolutionary change that transforms their hands and arms suitable for throwing rocks.

Stage 4. Communication And Mental Evolution

With teamwork and complex activities as using rocks to chase away predators from cave mouths, it is no surprise that the creatures are learning to communicate more complex messages! "I want a stone". "Go away". "Warning predator at the cave door"! "We go for hunting tomorrow". The influx of such vast array of information also necessitates a quick growth of brain. These are smart beings now! During these times somewhere sometime they invent writing. Caves start getting their share of paintings now onwards.

Stage 5. Fireworks!

Now the creatures learn the use of fire to cook food, to stay warm in winter nights and to protect themselves from predators using fire torches. This also invariably necessitates the use of simple stone tools to cut dry wooden branches for torch building.

Stage 6. Wood People

The creatures learn woodcratfing. Using wood to form not only torches, but weapons including maces, spears (tipped with stones), staffs and even atlatls. Now the creatures start venturing out of the caves for extensive periods.

Stage 7. First Cities

Being able to protect themselves from the flying predators now, the creature build first cities. During this time, they also get to invent the bow and arrow. By this time, they have learnt more than just drawing images. The first formal written language begins!

The rest of social evolution you can design yourself, depending on plot requirements and the planet's environment.

  • $\begingroup$ I wonder how the first cities can be protected from burning down? This is part of my major concern with this high oxygen world... $\endgroup$
    – rumguff
    Commented Sep 10, 2015 at 17:28
  • $\begingroup$ These intelligent creatures focus more of their building on cut-stone and/or have a highly organized fire fighting corps. $\endgroup$ Commented Sep 10, 2015 at 18:30
  • $\begingroup$ The buildings are made not of wood (as in the west :p) but of stone pieces, stuck together by clay (as you see in some eastern countries). Adobe structures, as they call them. They have zero tendency for catching fire. What you do need is => a) all the woodwork used in the buildings is coated with a thick layer of clay. b) the cities are made OUTSIDE the forests (close to mountainous regions) where they cannot be affected by forest fires. c) for firefighting, these creatures use asbestos (a chemical) which is abundant on some places near the mountain ranges. asbestos is very effective! $\endgroup$ Commented Sep 11, 2015 at 2:22

I would like to point out that the intelligent species on this world may well be derived from an arthropod like creature. This world as you describe it is very similar to earth in the Carboniferous time period. The high oxygen, temperature stability, and generally higher humidity lead to creatures like:

Arthropleura - A millipede that reached lengths of 2+ meters
Pulmonoscorpius - 28 inch long scorpions

Arthropods of course have tough out shells and if adapted to your world may have a reasonable fire and heat tolerance.


No humans, and no vegetation. Burning of everything in reach anytime rocks fall, lightning strikes, static electricity builds up, etc.

At 30% oxygen concentration, wet vegetation is flammable, and humans are equivalent to paraffin.

If you survive that: Hyperoxia. Inflammation of the lungs. Aseptic bone necrosis. Respiratory acidosis (and ultimately toxicity). Inert gas narcosis. Oxidative stress.

Making a planet habitable for humanoids: The planet

  • $\begingroup$ Hi user3082. It seems to me that having evolved in such an environment, any creature would have evolved to not be readily flammable in that environment (or they wouldn't have got so far through evolution as they have). This answers appears to just assume the same biochemistry that we have, dropped into a very different environment, which obviously has many problems; everything becomes quite different when a creature has evolved in that environment. $\endgroup$
    – user
    Commented Sep 23, 2015 at 13:32
  • $\begingroup$ No, mostly it assumes chemistry. Question says: "burning down of large swathes of biomass." Please show me a biomass that's both flammable and that doesn't burn readily in a high oxygen environment. You can evolve all you want, but you can't be both flammable and inflammable. Granted, should take out references to humans. $\endgroup$
    – user3082
    Commented Sep 27, 2015 at 9:27
  • $\begingroup$ I knew I had seen it somewhere. According to this answer, estimates of oxygen content in Earth's atmosphere some 300-400 million years ago are as high as possibly over 35%, and certainly possibly over 30%, with the low estimate around today's level (approximate figures all, going by eyeball measure; see the linked answer). Since life on Earth didn't completely die out around that time, obviously such levels of oxygen content in the atmosphere are survivable. (But, obviously, perhaps not for creatures more comfortable at 20% O2 content.) $\endgroup$
    – user
    Commented Sep 30, 2015 at 20:55

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