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There are also microorganisms as deep down as we can drill underground. I've seen speculation that that's how life rebooted after ancient disasters. If life e

There are also microorganisms as deep down as we can drill underground. I've seen speculation that that's how life rebooted after ancient disasters. If life ever existed on Mars, I expect it's still there deep underground.

andrewflnr 1y ago
I think "ancient disasters" must be referring to the Late Heavy Bombardment, which is the only putative disaster I know of that could have sterilized the surface. Though it was supposed to fully re-liquefy the crust, so even underground life surviving would be dicey. https://en.wikipedia.org/wiki/Late_Heavy_Bombardment https://en.wikipedia.org/wiki/Late_Heavy_Bombardment
- maxbond 1y ago
  It's possible life existed in the Hadean epoch before the Late Heavy Bombardment, but for the most part there are no rocks from the Hadean epoch so it's difficult to say whether there was life. Those rocks were swept into the mantle. There's a tiny bit of evidence for it from isotopic ratios within Zircon crystals which have survived that long (they are robust enough to survive the mantle and resurface), but it isn't definitive. Much like a sibling comment notes that we haven't been able to drill deep enough to find a depth without life, we haven't found rocks old enough to prove the nonexistence of life at any point in time, but if those rocks do exist they are no longer on Earth (eg they were ejected during an impact).
HarHarVeryFunny 1y ago
Even the worst of Earth's exinction events, the Permian–Triassic extinction event (aka "The Great Dying"), didn't kill off everything at surface level, even though that one did kill ~80% of marine species and ~70% of terrestial vertebrates. Earth's habitats have fluctuated wildly from changes in temperature, atmosphere, oceanic acidity, etc, but life is so diverse that some species have always been able to survive. It's basically a worst case scenario of "punctuated equilibrium" which is the norm for evolution - life doesn't evolve gradually in the way you were taught in high school but rather populations of species, and entire species, drift genetically over time, accumulating benign genetic changes until the environment changes in some major way (drought, disease, catastrophe) when their previously benign accumulated changes may prove to be critically beneficial, and other populations/species die off. Given how badly humans are currently messing up the planet, especially wrt self-inflicted global warming, I take some comfort in realizing that even if we manage to screw things up so badly that we go extinct, that life will find a way, and life on earth will - given enough time - bounce back in some new and interesting way.
- LargoLasskhyfv 1y ago
  > ... bounce back in some new and interesting way. Possible, but doubtful(depending on how long it takes) because of the many, many things listed here: https://en.wikipedia.org/wiki/Timeline_of_the_far_future https://en.wikipedia.org/wiki/Timeline_of_the_far_future
  - HarHarVeryFunny 1y ago
    Those sorts of things have happened in the past too - I'm talking timeline of hundreds of millions of years.
    - LargoLasskhyfv 1y ago
      Yes. I know this timeline too :-) But what I meant to say with depending on how long it takes, was something about our Sun going red giant, expanding behind the orbit of Mars, and thus including Earth. But long before that happens, it will probably cook and irradiate Earth due to instability in that transition.
      - HarHarVeryFunny 1y ago
        Of course, but our sun going red giant is billions of years away, and will happen regardless of whether we're still here, taking good care of the planet, or not. I'm talking about what happens while earth is still in a livable state, even if maybe not for us. In the space of billions of years there could be many dozens of highly successful new eras of life each lasting hundreds of millions of years. From an evolutionary perspective humans are not the big deal that we think we are - we've only been around for a few millions of years (homo sapiens only for a few hundred thousand years) vs phases of life such as Triassic, Jurassic, etc that lasted for hundreds of millions of years. We may well wipe ourselves out via nuclear war, global warming, etc in the blink of an evolutionary eye, say in next million years - a failed experiment in intelligence that proves to not be sustainable, to be replaced by successive waves of new life exploring different directions.

andrewflnr 1y ago

I think "ancient disasters" must be referring to the Late Heavy Bombardment, which is the only putative disaster I know of that could have sterilized the surface. Though it was supposed to fully re-liquefy the crust, so even underground life surviving would be dicey. https://en.wikipedia.org/wiki/Late_Heavy_Bombardment https://en.wikipedia.org/wiki/Late_Heavy_Bombardment

maxbond 1y ago
It's possible life existed in the Hadean epoch before the Late Heavy Bombardment, but for the most part there are no rocks from the Hadean epoch so it's difficult to say whether there was life. Those rocks were swept into the mantle. There's a tiny bit of evidence for it from isotopic ratios within Zircon crystals which have survived that long (they are robust enough to survive the mantle and resurface), but it isn't definitive. Much like a sibling comment notes that we haven't been able to drill deep enough to find a depth without life, we haven't found rocks old enough to prove the nonexistence of life at any point in time, but if those rocks do exist they are no longer on Earth (eg they were ejected during an impact).

HarHarVeryFunny 1y ago

Even the worst of Earth's exinction events, the Permian–Triassic extinction event (aka "The Great Dying"), didn't kill off everything at surface level, even though that one did kill ~80% of marine species and ~70% of terrestial vertebrates. Earth's habitats have fluctuated wildly from changes in temperature, atmosphere, oceanic acidity, etc, but life is so diverse that some species have always been able to survive. It's basically a worst case scenario of "punctuated equilibrium" which is the norm for evolution - life doesn't evolve gradually in the way you were taught in high school but rather populations of species, and entire species, drift genetically over time, accumulating benign genetic changes until the environment changes in some major way (drought, disease, catastrophe) when their previously benign accumulated changes may prove to be critically beneficial, and other populations/species die off. Given how badly humans are currently messing up the planet, especially wrt self-inflicted global warming, I take some comfort in realizing that even if we manage to screw things up so badly that we go extinct, that life will find a way, and life on earth will - given enough time - bounce back in some new and interesting way.

LargoLasskhyfv 1y ago
> ... bounce back in some new and interesting way. Possible, but doubtful(depending on how long it takes) because of the many, many things listed here: https://en.wikipedia.org/wiki/Timeline_of_the_far_future https://en.wikipedia.org/wiki/Timeline_of_the_far_future
- HarHarVeryFunny 1y ago
  Those sorts of things have happened in the past too - I'm talking timeline of hundreds of millions of years.
  - LargoLasskhyfv 1y ago
    Yes. I know this timeline too :-) But what I meant to say with depending on how long it takes, was something about our Sun going red giant, expanding behind the orbit of Mars, and thus including Earth. But long before that happens, it will probably cook and irradiate Earth due to instability in that transition.
    - HarHarVeryFunny 1y ago
      Of course, but our sun going red giant is billions of years away, and will happen regardless of whether we're still here, taking good care of the planet, or not. I'm talking about what happens while earth is still in a livable state, even if maybe not for us. In the space of billions of years there could be many dozens of highly successful new eras of life each lasting hundreds of millions of years. From an evolutionary perspective humans are not the big deal that we think we are - we've only been around for a few millions of years (homo sapiens only for a few hundred thousand years) vs phases of life such as Triassic, Jurassic, etc that lasted for hundreds of millions of years. We may well wipe ourselves out via nuclear war, global warming, etc in the blink of an evolutionary eye, say in next million years - a failed experiment in intelligence that proves to not be sustainable, to be replaced by successive waves of new life exploring different directions.