I just rolled up the most horrendous "habitable" planet ever.

[Varyon]

Originally Posted by David Johnston2

I'm thinking migratory animal species predominate, while the plants have very durable seeds. The microflora and fauna would be able to cyclically produce extremophile offspring

There's the question of how life got started in the first place with the primordial soup getting boiled each season. Might it have originated underground, where it would be a bit shielded from the extremes? If so, you might have most life still being underground, but migratory plants and later animals might be able to survive on the surface.

[J. Edward Tremlett]

Originally Posted by Varyon

There's the question of how life got started in the first place with the primordial soup getting boiled each season. Might it have originated underground, where it would be a bit shielded from the extremes? If so, you might have most life still being underground, but migratory plants and later animals might be able to survive on the surface.

Maybe it started out "normal" and then something happened to the planet to set it on its current orbit. If the effect wasn't cataclysmic, but gradual, life could have evolved to this point.

[David Johnston2]

Originally Posted by Varyon

There's the question of how life got started in the first place with the primordial soup getting boiled each season. Might it have originated underground, where it would be a bit shielded from the extremes? If so, you might have most life still being underground, but migratory plants and later animals might be able to survive on the surface.

It's an old system. The planet used to rotate faster and the atmosphere used to be thicker.

[Johnny1A.2]

Originally Posted by Lancewholelot

That is speculative and still the stuff of science fiction. No human has ever been born off the Earth's surface. The long term effects of low to no gravity on viable human development are unknown.

Fair point. But even that is correctible by an advanced/large enough techbase/economy. Centrifuges can be built, for ex. It might never be practical, but it's possible in principle.

Which is my point, the boundary of 'habitability' depends on the technology and economy available.