I'm going to say refrigeration. It allows food (and medicines) to be kept longer, transported further without spoiling, and even sold/consumed out of season.
Enabling our kind to record and propagate our words and knowledge across time and distance. To me, modern society is impossible without it.
This post was edited by Don Barzini at August 5, 2019 1:43 PM MDT
The apostrophe. No, the hyphen. Wait, the dash. Um, may I change my answer back to the hyphen, please? Final answer. Did I mention the asterisk? Never mind, never mind; stick with the dash. Hold on, I think I was right the first time, I’ll go with apostrophe. ~
Not so much "inventions" as three "discoveries" or "developments.
1) That of producing metals from their ores, and working those metals. Particularly Iron, which requires coke derived from coal for its smelting; and much later, Steel from that iron.
Iron and its alloys (the steels) permeate EVERYTHING else we have or use in life including whatever you are reading this on, even if those metals are not directly present.
2) The Wheel - and think far beyond the obvious wheels on vehicles etc., to such fields as rotating machinery.
3) Mathematics - like iron, also utterly ubiquitous and essential to utilising both of the above.
Without those three we'd be unable to ponder it here. We would still be living in the Neolithic.
Possibly fire. But taking the broadest meaning, it could be the first realisation that the environment could be manipulated to useful human purpose - in making purpose-built shelters rather than relying on natural huddling places like caves, or chipping flint into useful tools or sharpening sticks into spears. Once man gained a foothold though the simplest, easiest to hand, aids to survival, he could then turn his thoughts towards manufacture of pots, pans, window-glass, furniture, and to art, machines and weapons of mass destruction.
Yes, it may have been the first really, no-turning-back, breakthrough invention of man (but pre Sapiens I think). When I see Durdle, I think of Durdle Door - perhaps you can see it from your attic window Durdle, or perhaps not. I can see Georgian Bay from my window, and hear the breakers on a rough day, but big though it is, a lake is not the same as the sea.
Walt O'Reagun 