Cyanobacteria reproduce rapidly in sunlight and their numbers are mostly kept in check by viruses. If you bred a species that didn't have any existing viruses there would still be amoebas, flagellates, etc which would use the extra food to reproduced faster and keep the numbers in check, though it would be a big ecological problem. If these couldn't eat them because the new cyanobacteria was mirror life they they'd lock huge amount of carbon from the biosphere as indigestible sugars and starving all other plant life, over the course of maybe a year at the most.

It's possible that humanity could survive by exploiting things like fossil fuels but by default it would be as bad as the extinction that ended the Permian. And certainly most humans would die.

We're protected from this naturally because it takes over a billion years to evolve something as good at reproducing as cyanobacteria from scratch and any biogenisis that were to happen in the modern world would produce something so hapless it would be swiftly out competed for resources. You can't evolve from a regular bacteria to a mirror bacteria, evolution is really bad at making multiple changes at once and this would require changing literally every part of an organism at once.

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danwills 2 days ago | parent [-]

What a thoughtful comment! I concur that the chance of mirror-life 'evolving naturally' (or "in the wild" let's say) is basically zero, but then I imagined a future cell-printing machine that 'wild' humans might make that prints (maybe at near the atomic level), and that made me wonder whether given such a printer you could just swap to opposite-chirality (mirror) ingredients, and maybe mirror the 3d plan that you're printing? Doesn't seem that far fetched if we ever get printing at a very small scale level? But then I remembered a cell is more like a wave than a static object, so all of the above are probably meaningless ramblings.. but all in the spirit of curiosity!

I am not alarmed by the possibility of mirror life because I think it would be at a disadvantage to all other life on earth at present, so it probably wouldn't get very far. (famous last words!?)

	▲	Symmetry 2 days ago \| parent [-]
		That would definitely be possible but if humans had the kind of molecular nanotechnology that could do that I'd be much more confident in our ability to whip up some phages to counter the threat.