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?