Don’t worry. If there is anything history (and the geological record) has shown us, the planet and other humans have tried very very very hard to kill all humans in the past. And failed.
Not that they didn’t make one hell of a dent sometimes, mind you.
Actually, the geological record shows that mass extinctions are possible, happen somewhat regularly, and are sometimes caused by a single species altering the environment on a massive scale. For example when photosynthesizers converted 20% of the atmosphere into extremely toxic oxygen gas.
Eh, a bit overstated. None of them killed EVERYTHING, near as we can tell. Not even the oxygen catastrophe you're mentioning.
To do that would likely require liquifying the mantle entirely, or some similar scale event.
The last big one was approximately 66 million years ago due to perhaps the Chicxulub impact, and it wiped out most of the dinosaurs - but modern birds are descended from them, and the crocodiles and alligators survived (well, VERY similar looking ancestors) /just fine.
None of them could build space stations, nuclear reactors, bunkers, etc. That we know of at least. None of them could grow hydroponic food, or communicate at near light speed to the other side of the planet, or even know what any of that means.
The entire span of time something vaguely resembling human has been around is also 1/10th of that time, but there have been MANY smaller events with large scale extinctions.
I'm not saying it would be a good time, but there is no way every single human is getting wiped out by anything except a nearby Gamma Ray burst/Supernova, surprise planetary collision, or something of similar destructive scale. Things way beyond even our wildest dreams of destructive power.
Even if we launched every nuke every country has ever produced, while civilization as we know it would be done for, humanity would definitely persist. Even if the next war would be fought with clubs instead of nukes.
And even if all the oxygen in the atmosphere turned to cyanide - guess what, we do (technically) know how to deal with that, there are populations of people who are currently protected from that, and while most of humanity would die while we scrambled to adapt, humanity itself would not perish. At least not just from that.
Hell, not that long ago the most technologically advanced society of the time (Nazi Germany) with a massive and state of the art army tried to exterminate a subset of humans (Jews, Homosexuals, Roma) using massive force, the latest technology, and with a near single minded focus.
And while they did kill a lot of people and perpetrate terrible crimes, they also failed rather completely at the task. Even in areas where they were literally burning everything to the ground.
What makes you think they would have been more successful if they’d also been trying to kill themselves at the same time? Hence impeding their abilities?
And humans are, near as we can tell, the most lethal animals on the planet overall.
Humans survive implausibly terrible situations on the regular, and are currently living in every major ecological niche in the environment except perhaps the very deepest parts of the ocean. Though if we count military submersibles and oil rig diving bells, they too are ‘occupied’.
Would lots of people die, and would it be terrible if an environmental catastrophe occurred? You bet. But killing all humans is even less plausible than killing all ticks, or all roaches. Humans, the most lethal species on the planet, keeps trying and failing to do so.
Short of melting the mantle underneath us anyway. We do have some folks living in a space station. Probably not enough though.
Nazi Germany failed because they used a method that did not scale well. Also because they were trying to exterminate one set of humans while preserving another set. Exterminating all humans together is easier - perhaps flood the oceans with dimethylmercury - the geological-scale equivalent of curing cancer with a flamethrower. Or, just dig up all the fossil fuels and burn them.
That is why eating too much Tuna will give you mercury poisoning. And the Nazis literally used nerve agents (Zyklon B) among other things. Nasty nerve agents (and most household pesticides) came out of WW2 research largely done by the Nazis (through Bayer, as it turns out).
And the moment anyone got wind of an attempt to try to do such a thing, enough humans would go to ground you’d never actually succeed. Hell, enough are probably already under ground for whatever reason you’d never succeed even if you did manage to catch the whole world by surprise and somehow actually release it all at scale.
The Nazi’s did not fail because they failed to try to kill humans at scale. Frankly, they did it at the largest scale since probably Ghenghis Khan. Certainly in a far more industrial fashion.
The issue is that it’s actually really hard to kill a lot of humans. Something that personally warms the cockles of my very human heart.
Embrace your ancestry of murderous (and loving) hominids, and aim to use it to make things better. Rejecting it is a false path.
Actually Zyklon B came out of WWI research, and in the interim it was licensed worldwide for use as a fumigating agent. Including from 1929 onwards in the United States, where it was used by the Public Health Service to fumigate freight trains and clothes of Mexican immigrants entering the country.
