Flourishing chemosynthetic life at the greatest depths of hadal trenches
nature.com
nature.com
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.
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.
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.
Possible, but doubtful(depending on how long it takes) because of the many, many things listed here:
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.
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).
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.