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

[Varyon]

Originally Posted by Johnny1A.2

It isn't only ever false, though. Earth exists. It's the one definite True we know about, but it does exist.

Having the question "Is this planet habitable?" basically work out to be the same as the question "Is this planet Earth during the Holocene?" doesn't really accomplish much for you. Granted, a better question for the first one is "How habitable is this planet?" so that rather than a "Yes/No" answer you can have a range. A very habitable planet would be one where a person with minimal to no training could be dropped in naked and expected to thrive, this would progress into things being harder (needing more training and/or gear), eventually to the point of being largely indistinguishable from being a space habitat with more reliable gravity (and also progressing even further, with the habitat needing to be more resilient than a space habitat - like one in a gas giant or perhaps on a highly-volcanic planet).

[David Johnston2]

Originally Posted by J. Edward Tremlett

Trying to imagine how life could evolve there. It'd be constantly undergoing boom and burn cycles and have to find a way to cocoon.

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

[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.

[Varyon]

Originally Posted by J. Edward Tremlett

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.

Kinda hard to imagine something less than catastrophic changing the orbit so drastically. I guess in theory you could have a lot of close passes by rogue planets (or even just other planets in the same system) that pull it a bit out of its original orbit each time until it's eventually in the crazy boom-or-burn orbit. That seems pretty low probability... but maybe no more so than life managing to evolve on a planet that always had such an orbit.

[J. Edward Tremlett]

Originally Posted by Varyon

That seems pretty low probability... but maybe no more so than life managing to evolve on a planet that always had such an orbit.

It's a darn weird universe. Let's keep it that way.

[Johnny1A.2]

Originally Posted by Varyon

Having the question "Is this planet habitable?" basically work out to be the same as the question "Is this planet Earth during the Holocene?" doesn't really accomplish much for you. Granted, a better question for the first one is "How habitable is this planet?" so that rather than a "Yes/No" answer you can have a range. A very habitable planet would be one where a person with minimal to no training could be dropped in naked and expected to thrive, this would progress into things being harder (needing more training and/or gear), eventually to the point of being largely indistinguishable from being a space habitat with more reliable gravity (and also progressing even further, with the habitat needing to be more resilient than a space habitat - like one in a gas giant or perhaps on a highly-volcanic planet).

Yes, it's going to be a range. One reasonable definition of 'habitable' would be something Anne McCaffrey expressed in the intro to one of her Pern novels:

...third planet was enveloped by air Man could breathe, boasted water he could drink, and possessed a gravity that permitted Man to walk confidently erect.

That's a pretty good quick-and-dirty definition of 'habitable planet'. Of course it leaves lots of room for ugly surprises (and that particular planet held one in her story).

[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.