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Premise

We have found extremophiles of the aquatic and microscopic types here on Earth, but so far large terrestrial extremophiles are the stuff of conjecture only. This makes it somewhat challenging to speculate whether terrestrial creatures could survive on a moon heated by tidal forces of a large nearby planet/geo-thermal heat.

I'm trying to envision a realistic scenario in which cold-blooded creatures (more precisely known as ectotherms) inhabit a moon orbiting a planet far from the habitable zone. Here is what we are working with:

  • Assume the moon has everything needed to support life as we know it (magnetic field, breathable atmosphere, geo-thermal heat, ect)
  • Assume the ectotherm to be a very large lizard, say a komodo dragon

We might feel inclined to clap our hands together and say 'voila! we're done!' However, further analysis leaves us apprehensive about a large terrestrial ectotherm surviving on a such a moon solely on geo-thermal heat. A moon heated via tidal forces from a its parent planet will presumably be very geologically active. One second our lizard-like ectotherm is enjoying a nice soak in a hot spring, then BOOM: he's consumed by a pyroclastic flow from one of the many volcanic eruptions.

Question

Given that tidal force warmed moons can be overly dangerous (take Io for instance), is there a more, shall we say, "peaceful" way of allowing for the survival of large terrestrial ectotherms on a moon outside of the habitable zone? If I must resort to large tidal forces inducing geo-thermal heat for ectotherms on this moon, then how will the large ectotherms cope with the geologic upheaval that comes with such a world?

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    $\begingroup$ So far large extremophiles in any environment are the stuff of conjecture, the biggest extremophiles known are colonial single celled. $\endgroup$
    – Ash
    Jul 2, 2018 at 15:59
  • $\begingroup$ @Ash Pardon my hyperbole; I didn't realize the Marianas Trench tube worms were actually colonial single celled. They resemble a complex life form. The extremophile segment isn't necessary for the actual analysis of the question anyway. I just wanted to set the stage and put things into context. $\endgroup$
    – Arash Howaida
    Jul 2, 2018 at 16:06
  • $\begingroup$ Weirdly enough Riftia pachyptila, the giant black smoker tube worm, isn't considered an extremophile, go figure. $\endgroup$
    – Ash
    Jul 2, 2018 at 16:14
  • $\begingroup$ @Ash yea, that is strange. It's kind of like a brilliant scientist who never gets the title of Nobel prize. The black smoker tube worm is a tough act to follow, I guess it's just hard to make it into the extremophile club $\endgroup$
    – Arash Howaida
    Jul 2, 2018 at 16:22
  • $\begingroup$ that pretty much a description of life on earth, highly geologically active. many such creatures live on volcanic islands with frequent eruptions. if anything it makes for richer ecosystem by constantly resupplying nutrients. $\endgroup$
    – John
    Jul 2, 2018 at 19:04

3 Answers 3

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This makes it somewhat challenging to speculate whether terrestrial creatures could survive on a moon heated by tidal forces of a large nearby planet/geo-thermal heat.

Eh, not really. You don't need large extremophiles. You only need single-celled extremophiles to form the base of the food chain right up close to thermal vents and cold seeps. Larger creatures can exist in the less-extreme zones at varying distances away from the ecological energy source. There are, after all, plenty of non-extremophile complex animals living around volcanic vents on Earth.

One second our lizard-like ectotherm is enjoying a nice soak in a hot spring, then BOOM: he's consumed by a pyroclastic flow from one of the many volcanic eruptions.

Yup. Or, less spectacularly, the vent dies out and everything in the vicinity slowly starves. But that doesn't mean all life ends, or even that that specific species necessarily goes extinct.

then how will the large ectotherms cope with the geologic upheaval that comes with such a world?

Easy: they migrate. If all life depends on a single volcanic vent, you're screwed. But it wouldn't. Life would exist in oases surrounding thermal vents and cold seeps all over, with organisms migrating between them Your ectotherms don't need to be able to thrive in cold areas between oases, but they do need to be able to survive the trip somehow--either by simply moving very slowly, or going dormant and hoping to eventually get blown back into a warm area by the currents / winds, or by hitching a ride with an endothermic creature. Every once in a while, the population at one particular oasis which falls victim to a major eruption will be wiped out--but that's no big deal. It will be re-colonized again by imports from other thermal oases that didn't all get wiped out at the same time. Maybe a few indigenous species go entirely extinct, but the ecosystem as a whole recovers, and new ones will evolve.

This is exactly how thermal vent communities work on Earth.

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  1. Your creature is large because it needs to be. It needs to be able to move fast. Consider an event like a red tide - lots of small animals are killed because they cannot outrun the red tide. Large animals put it in gear and get out of there. So too your lizard. If stuff starts getting iffy where it is, it heads for higher ground.

  2. Your lizards can detect signs that badness is coming. Like the famous elephants which can feel the coming tsunami thru their feet, your creature feels changes in the moons geomagnetic field which augur trouble.

  3. Your creatures get killed a lot. Even with these skills, lots of lizards do die in disasters. But this is OK because

  4. There are a lot of lizards. There are enormous amounts of food for them on this fertile moon and they have a very rapid reproductive rate. Even if a catastrophe wipes out every lizard for miles, these fecund and highly mobile lizards will quickly repopulate the area and take advantage of the food resources made available after the geologic turnover.

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Tardigrades can survive in such a condition as they are resistant to everything(except things that actually harm them like defence from predators)

(let say a species of tardigrade evolves to be large but still retain it's original resistance to radiation, heat, absence of air, etc. It may survive said condition and still be large enough to fit the description)

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    $\begingroup$ Tardigrades don't really count as "large", though. Otherwise, I suppose this would be what Arash is looking for, but size is the issue. $\endgroup$
    – HDE 226868 ♦
    Jul 2, 2018 at 16:02
  • $\begingroup$ it might increase in size maybe because of let's say more food for the tardigrade , therefore it will be more nourished and have more energy , and therefore over many generations will be a large species of tardigrade. $\endgroup$
    – Persivefire
    Jul 6, 2018 at 12:02

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