Milestones in the development of an exotic biosphere

My present grand exercise in yak-shaving is to develop a pseudo-random procedure for a computer to eat a star catalogue and spit out a collection of sheets of stats for inhabited planets that will be plausible enough for gaming, and that won’t compel my players to point out “obvious” impossibilities. I’m up to the point now where I have to generate a biosphere that is compatible with the planet’s surface conditions and age, so that I can tell whether it has such conveniences and features as an oxygen atmosphere, soil, forests, animals with feelings, sophonts with tools, sapients with language and culture, farms, herds, cities, motorised vehicles, space-flight, post-holocaust wastelands.

I’ve skimmed some palaeontology, but it strikes me that some of the things that were crucial milestones in Earth’s evolution and of paramount importance to palaeontologists — e.g. the development of the eukaryotic cell by endosymbiosis — (a) won’t work out that way on an exotic planet, or (b) won’t effect a gross feature of the planetology and ( c) won’t affect human colonisation.

I would value your thoughts. What are the key steps in the development of a biosphere, for an exotic planet?

From a hard-SF narrative point of view, a planet should have one distinctive feature that drives the rest of the weirdness – like the principle of economy of miracles. Mesklin runs from 3g at the equator to several hundred at the poles, and the rest flows from that. But this might be implemented as an “is this interesting” rule at the end of generation rather than as a process during it.

I guess you can make more generic milestones which are more “achieving a specific effect” rather than “stick a label like eukaryotic on it”.

For instance…

  • Whatever you breathe (oxygen, methane or whatever) accumulates in sufficient quantities for multicellular life to be possible. Or for slime moulds to aggregate permanently (Oxygen is the most likely candidate for respiration, because of the redox tower and the amount of bang it gives for its buck, compared to other Earthly options. But if you have a chemistry where creatures are breathing molten tin, the same principles apply). The organisms are still small (or thin), because oxygen (or whatever) has to diffuse into the middle of the bundle of cells.

  • Once you have an organism which is a collection of cells, those cells can take on specialist roles. One of those is shunting nutrients and/or oxygen around the body… which means you have busted the “only by diffusion” limit and can get big. By big, of course that still includes things that we think of as tiny, like greenfly and ants! :slight_smile:

  • Evolution of eyes/vision (or echolocation or whatever) - once you have a system that can see the world around it, you can become fast. Reaction speeds and sophistication of vision get into an arms race, especially if mating or predator-prey interactions are on the cards.

  • Life moves onto land from water. You can use Earth as a baseline for how long that takes. Gravity will influence the amount of time the transition from water to land takes (and later how long it takes to evolve flight). C.J. Pennycruik in Newton Rules Biology looks at the influence of gravity on the cost of lugging your body around:

On a planet with gravity much lower than Earth’s, the ‘cost of transport’ for swimming would be higher than for walking or flying, whereas on a big, high-gravity planet the reverse would be the case. Creatures evolving on a low-gravity planet would more readily take to the air, whereas those evolving in high gravity would be quick to take to the water, or reluctant to leave it in the first place.

  • Land animals figure out how to eat land-plants. A side effect of plants taking to the land is that they have to strengthen their tissues with tough compounds like cellulose and lignin. This is to enable them to grow upwards to reach the sun, support themselves when not buoyed up by water, etc. Any molecule which is physically tough is also difficult to digest. The first land animals did not eat plants - they ate decaying plants and each other. That includes all those giant amphibians of the Devonian. The arthropods cracked eating plants long before the vertebrates. Because the vertebrates first had to sort out getting their nose involved in breathing, enabling them to breathe and chew (gum) at the same time. They didn’t work out how to do that until the early amniotes came on the scene. Alien creatures will have different anatomy and different obstacles/advantages to becoming herbivores.

  • Land animals cut their ties to water for breeding. You invent a hard shelled egg (cleidoic egg) or live birth of offspring which are not “tadpoles/midge larvae”. Once that is done you can head inland to colonise all those continental interiors, rather than hugging riverbanks/seashore and lurking round lakes.

  • Land animals invent warm-bloodedness (endothermy). Hurrah! You can now colonise cold latitudes and can live there all year round - no more compulsory migration in winter. (Though migration or hibernation remain good strategies for many creatures).


I want to say that planetologically, perhaps the most important effect of life is the creation of an atmosphere far from chemical equilibrium. On earth, that means lots of free oxygen (if photosynthesis stopped it would be gone in less than a million years, according to estimates I’ve seen); but it could be other reactive gases such as chlorine or perhaps ammonia. Science fiction in the old days used to assume that planets just had one atmosphere or another, and that whatever life they had would breathe what was available; but now it appears that one category of organisms excrete toxic waste gases and another category evolve to use those wastes as metabolic superchargers (while taking biochemical safety precautions in their use)—and in the process change the geochemistry of the surface.

Oh, and I think you can say “I created new life—shit, I’m a god now!”

Yeah, followed in importance by soil, forests, farms, and spaceports.

The shorter I make my list of key developments, the more intermediate steps get chunked together into each key development, the closer the Erlang-k distribution of the time taken to reach the milestone converges to Gaussian normal and the easier the modelling becomes. But I don’t want to overlook anything important that would make a difference to the prospects for human settlement or the experience of visiting PCs.

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Why forests? Do bamboo forests or Devonian lycopsid (giant club moss ‘trees’) in swamp forests count? I’m wondering if you’re wanting timber/bamboo as human building material, or fossil forests for prehistoric carbon-capture and thus modern coal reserves…

If there is a minimum percentage of forest cover you need in your model, you’ll have to tweak if for portions of planetary history: “Oh dear we’re at the height of an Ice Age and all the forests have massively died back”. I guess unless your minimum forest cover is Earth at glacial maximum.

Pleistocene glacial maximum! Not Snowball Earth glacial maximum. :slight_smile:

Possibly useful paper on the interaction between tree roots and soil formation in the Devonian:

Native forests aren’t terribly important for my purposes, because I don’t run exploration or pioneering campaigns or adventures, and have only twice ever had player characters castaway on or kidnapped to an un-terraformed planet. The worlds that player characters go to in my Flat Black adventures have all been terraformed, and all have forests (of Terran tree species, sometimes modified). But I’d like to make this conversation a bit more general, so I supposed that other readers might have wider interests than I.

Forests, and especially a history of having had forests for hundreds of millions of years, is of some definite planetological importance. Large plants have extensive roots; extensive roots are likely to be deep, and that makes a local difference to water tables and the mechanical and even chemical weathering of bedrock, and I think that perhaps large plants in the informal category of trees are a bit more apt to form such large accumulations of raw material for making coal measures of than, say, the exotic equivalents of peat mosses and turf. And then you have forests as a biological reservoir of carbon to complicate the carbon cycle — though the biological carbon reservoir is a bit prone to be unstable on a shorter time-scale than we that which we generally ignore in planet generation. You’re right to question whether all that is finer detail than we generally gloss over in this sort of work.

I was thinking of three other things.

  1. Like cleared and cultivated fields, forests are a conspicuous visible feature of a planet that I want to know about when I describe what player-characters see when they stand at the top of the landing stairs on arrival on a new world. Expanses of dark green across the humid latitudes of a planet seen from orbit could be verdant tangles of low-growing vegetation, made up of non-vascular plants like bryophytes that do not grow tall trunks. But when the character reaches the surface the GM will want to know whether to describe towering forests or a green steppe.

  2. Forests provide concealment from aerial and orbital search and surveillance for larger things than a heavy cover of non-vascular plants can. It’s easy to get lost in a forest or swamp around here, and you have to know what to do if you are—but a friend of mine from Iceland tells me that if you get lost in a forest there all you have to do is stand up. People on foot lost in a forest are hard to find by an aerial search — so are fugitives. Where there are extensive forests it is possible for searches and surveys to overlook villages, city ruins, migrations, military musters and movements, and even guerrilla camps that would be difficult to hide if there were no vegetation higher than a couple of metres.

  3. A forest is a distinctive environment to be in on a typical RPG adventure. My favourite SF RPG ForeSight provides rules for forest vegetation to inhibit travel (especially in vehicles), provide concealment, provide cover in firefights, and drastically reduced the range of encounters. PCs in Heavy Vegetation can be ambushed at “contact” range by enemies and dangerous game that they could blow away at 1200 metres with their target target target-designating laser rifles, were they on a grassland or low heath.

What do you make of that? Does it seem worth noting to you?

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It would be interesting to have a planet generation system that then spits out a terraforming difficulty level (which could be combined with tech to get a cost and time). That then lets the GM decide “was this planet worth terraforming, or do they just put people in sealed habitats and vehicles, or do they completely ignore it”.

(But I’m the GM who made several hundred GURPS aging rolls – on computer, of course – to get the future dates of the British monarchy. Which never came up in game.)

Anything the system can tell me about “what the planet is like” is useful, both for the general feel of the place and because it gives me some idea of what planet-specific local economy might be like. I’m rather guessing that in FB there isn’t a lot of planet-specific local economy because of the cost of interstellar shipping; so everywhere does a bit of mining, everywhere does a bit of agriculture, etc.

It was worthwhile. It tied that future to the present day in a way that many fictional futures don’t.

I suspect that is very much dependent on tech level; the effort you put in to the search vs size of the search area*; and processing power. Professor Challenger is on a budget, so his archaeology team can only survey a tiny portion of the Amazon rainforest looking for El Dorado. UNIT is using cutting edge orbital and aerial remote sensing and the world will end if they don’t find the ruins of El Dorado, so they dedicate the computing power of a several governments to the task. :slight_smile:

For plot reasons, of course, UNIT can be dedicating its resources to hunting for El Dorado rather than for the PCs after their latest skulduggery. :slight_smile:

*Like finding missing people in a completely barren, treeless desert is difficult if it is huge and your search systems comprise of a couple of aircraft and some eyeballs. That why they tell you to stay with the plane wreckage if you crash.

Oh, absolutely. But sometimes your PCs are James T Kirk and can scan a whole planet for “life-signs” in an instant, while other times they are Adam Reith evading Chasch or Dirdir search-parties in air-boats.