Good to know that there'd be something to reboot life if a giant meteorite hit the earth.
A thing that is rarely mentioned and I also do not see it mentioned in this article, is that these communities of organisms, even if they live in the dark, are sustained in a great proportion by the free oxygen dissolved in the water, which comes from above, from the phototrophic algae and plants.
Most of the energy that is used for chemosynthesis by the bacteria upon which all others feed, comes from the oxidation with free oxygen of the hydrogen sulfide that comes out from the oceanic vents. Only a small part of the bacteria present there are methanogens, which use free dihydrogen coming from the vents and carbon dioxide, to make methane. Except for the methanogens and for the even less abundant acetogens, most bacteria living there still depend on the solar energy captured by algae and plants. The same is true for all the animals present there, which feed on bacteria or on each other.
So if a giant meteorite would hit the Earth, preventing photosynthesis for some years, that could still wipe out most of the members of these chemosynthetic communities from the bottom of the ocean, because the water around them will be depleted in oxygen, killing even most of the bacteria.
Of course, at least most of the anaerobic bacteria will survive.
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.
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.
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
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).
If the Chixulub asteroid that wiped out the dinosaurs hit us today, humans would probably survive.
Even if over 99.99% are wiped out, that still leaves a decent number to figure it out.
It is estimated that human and human ancestor population has dropped as low as a few thousand in the past.
Life would be glum, but causing complete human extinction is not as easy as it sometimes appears.
A giant meteor hit the earth 66 million years ago. Life uh, found a way.
If we have to start over from microbes there probably won't be enough time to reach where we are currently before the Sun's expansion wipes us out.
hadal: relating to the zone of the sea greater than approximately 20,000 feet (6,000 m) in depth.
Thanks. Root of the word, Hades, obviously.