How would life survive...

[Salsacookies]

On a planet that changes from summers so hot there's no ice to winters so cold all water turns to ice, every decade? It is like this, Greenhouse Earth gradually cools over five years into a Snowball Earth, which then warms gradually into Greenhouse Earth in 5 years, as a continuous cycle every decade.

 

[SamIO]

I'd imagine a good option would be for life to favor oceanic biomes. The water would dramatically reduce the effect of temperature and weather changes, as well as dampen the intensity sheer as things fly from one extreme to another. Naturally, Terran fish wouldn't be too happy in this planet's saltwater, but I imagine it's a lot easier to adapt in the sea to this sort of decennial hazard than on land.

 

[Asuras]

Continuing off of Samster (as he's quite right)...

Water has a very high heat capacity, meaning it takes A LOT of energy to get it to increase by 1 degree in temperature. If a planet is big enough, with great enough gravity to maintain an Earth-like atmosphere, any water the star causes to evaporate will ultimately end up precipitating at some point anyways, so it's unlikely the planet will lose all of its water. Because of this, deeper waters will maintain a relatively stable water temperature regardless of surface temperatures. Creatures living down there won't suffer much in the way of extreme temperature shifts.

Now freezing, on the other hand, is a bit more likely to happen to deeper regions than getting too hot. Still, if a planet's core can generate enough heat (through hydrothermal vents, undersea volcanoes, etc) then ice will fail to take hold in deeper regions of the ocean. I can imagine organisms living on this planet would tend towards oceanic migration, moving closer to the water's surface during hot periods (homeostasis-energy benefits!), and sink down when the ice comes around.

Life on the surface is (logically) out of the question. Any evolutionary adaptation transpiring in amphibious organisms would take far too long (much, much longer than 10 years) to give any significant adaptation allowing them to live in such drastically-changing environments. Any organism that adapted to getting onto land (very poorly, albeit) would immediately die to freezing temperatures within the ten year span, thus ending that line of evolutionary change.

The likelihood of an organism generating advantages to both freezing temperatures and terrestrialization is just... well I wouldn't count on it happening in the lifetime of a universe. Anything on this planet that would adapt to cold temperatures would already be utilizing the benefits of going lower in the oceans, thus avoiding land.

Life on this planet would almost certainly be limited solely to aquatic lifestyles.

 

[Minibit]

You could also use "a wizard did it"!

And by that I mean the fantasy route can allow you to have a lot of freedom with this kind of setting!

• You could have a patron god of each cycle, who makes sure life survives the freezing/heating if they're feeling pleasantly toward said life (ie: are satisfied with worship/sacrifices)
• You could have the peoples of the planet develop spells and enchantments to ease the shift in cycles
• You could have most of the life forms on the planet exist in a stasis-like state through one season, and thrive in the other

 

[Immortal_Chaos]

Well maybe some kinda creature adapted to the heat that lives during the summer, but then lays some eggs that can stand the winter, to hatch in the summer?

 

[Immortal_Chaos]

You could also use "a wizard did it"!

And by that I mean the fantasy route can allow you to have a lot of freedom with this kind of setting!

• You could have a patron god of each cycle, who makes sure life survives the freezing/heating if they're feeling pleasantly toward said life (ie: are satisfied with worship/sacrifices)
• You could have the peoples of the planet develop spells and enchantments to ease the shift in cycles
• You could have most of the life forms on the planet exist in a stasis-like state through one season, and thrive in the other

Ooh, I didnt read the third dot point...

 

[Malkuthe Highwind]

Truth be told, I would like to know what causes such drastic--cyclic--shifts in climate on this planet. Maybe that can offer us some insight into how life could possibly survive--and thus evolve--on this planet.

 

[Rai'Athar]

Truth be told, I would like to know what causes such drastic--cyclic--shifts in climate on this planet.

Drastic--cyclic Milankovitch cycles.

Maybe that can offer us some insight into how life could possibly survive--and thus evolve--on this planet.

Life would evolve differently, especially plant life I'd imagine. Remember that plant life, dinosaurs (reptiles) and smaller mammals thrived in some of the warmest periods in earth's history. Plant life and mammals also survived multiple ice ages. This is definitely a world that could support the evolution of human life unless I've somehow misunderstood what the OP wrote.

 

[Kehvarl]

The big problem isn't going to be the freeze; sure that'll kill a lot of surface life (all of it if we're talking true snowball earth effect), but the equatorial regions wouldn't have that for the full 5 years. The real problem is going to come from the rapid temperature changes. 5 years to go from iced over to no ice at all is... incredible. You'd erode so much surface into the water that the term "topsoil" will be meaningless. Worse still, the rapid dump of meltwater will disrupt oceanic currents and destroy that thermal regulating system. You'll have hurricanes so powerful that "Class 5" won't be enough to describe it.

Humanity is basically a write-off at this point. Underwater dwelling is... hard. Very, very hard. Especially as you'll want to be below the thermocline to avoid the worst effects, and humans don't do well at that depth even with lots of equipment. Space it an option, but Oneil cylinders would be expensive to build, and hard to maintain; albeit more feasible than ocean-floor arcologies at our current engineering capabilities.

If we assume Kardashev 1 civilization, we could presume orbital solar arrays being used to gather solar energy and beam it to the earth to control the runaway climactic shifts. Beam more energy to heat the surface during the cooling cycle, and less during the warming cycle, combine that with high-atmosphere albeido-adjusters and you could geo-engineer a stable temperature gradient.

You could also create boreholes and use geothermal temperature regulation, geothermal power, artificial lighting for crops, and nuclear or thermonuclear generation to supplement the geothermal (you'll need it, humans use a lot of power). Overall though, unless it's a cycle that will stabilize in an unbelievably short timeframe (100 to 1000 years), you're still talking complete human extinction.


So.. Space habitats... huge, self-sustaining, repairable, space habitats. Or global scale geoengineering.

Would be neat to see the orbital pictures of Earth, devoid of anything like surface life and nearly completely obscured by multiple simultaneous Class 5 tropical cyclones though.