I'm my previous question I asked about the longevity of caves, now I'd like to figure out the longevity of the cave dwellers. Specifically, I'd like to put some bounds on how long they can hibernate.

Assuming these cave dwellers are not typical life as we know it (things like DNA and microscopic cells are optional), what biological traits could allow for them to hibernate for extremely long periods of time? Is it plausible for them to enter a dormant state that can survive being frozen or dessicated for millennia, or even geological time scales, only to become active again when thawed out hydrated? What biological traits would encourage that kind of resiliency when frozen?

I'm primarily interested in biological traits, either elvolved or genetically engineered, that would allow this longevity, however cultural and technical solutions (say some sort of enforced cryogenic or vitrification process) could work too.


2 Answers 2


You're going to have big problems with geological time scales: radiation.

The human body produces .29 mSv/year on average. By itself, not a big deal. However, in a zero-energy state like would be required there will be no radiation repair.

LD50 for a totally suspended human is 17,000 years even if the environment adds nothing. Divide this duration by 5 in a typical location.

Of course you could have something with a lot more radiation resistance than the human body. Nothing in the mammals does more than twice as well as a human, though. The simpler organisms do better but by the time you're up to a few million years in a typical environment even the hardiest are dying.

  • $\begingroup$ +1 I hadn't even considered the inherent radioactivity over geologic time scales as detrimental to an organism in suspended animation. Sounds like a job for the water bear. $\endgroup$ Commented Apr 15, 2017 at 2:57
  • $\begingroup$ @JoeKissling I was thinking of those water bears when I said even the hardiest are dying after a few million years. $\endgroup$ Commented Apr 15, 2017 at 4:13
  • $\begingroup$ I don't know about that, Water Bear lethal radiation dose is 5000 Gray, which depending on the type of radiation is anywhere from 5000 SV to 100000 SV. Using your figure for human body radioactivity means they could potentially be okay for anywhere between 17 million to 344 million years. Even dividing by 5 gives a substantial longevity $\endgroup$ Commented Apr 15, 2017 at 4:28
  • $\begingroup$ Interesting! Radiation was not an aspect I thought of. Seems like unless the critters are extremely rad-resistant, this puts the upper ceiling >10k years per generation. $\endgroup$
    – tinydoctor
    Commented Apr 15, 2017 at 6:06
  • $\begingroup$ @JoeKissling I thought that for radioactivity there was no adjustment, isn't it only neutron radiation that has more effect on the body? And neutron radiation is very rare for radioactive decay. 17My / 5 (for ambient radioactivity) = 3.2My. That's the few million years I gave before they're dropping dead of radiation poisoning. $\endgroup$ Commented Apr 16, 2017 at 3:11

Have a look at Water Bears, they are one of the most resilient organisms on earth. They are not actual extremophiles, but they have high resistance to wide range of temperature 1 K to 470K, high vacuum to 1200 atmospheres. They can survive dehydration and freezing because their body expands. Even direct exposure to space for 10 days, was not fatal to them. Water Bears have been observed waking from suspended animation after 120 years.


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