Many people would think that the likes of knowledge based invention as greatest, like math, written words, print on papyrus till the dawn of modern printing press, the birth of scientific method, and global knowledge sharing

However for just invaluable basics, the fundamentals of sustainable farming, sustainable husbandry, sustainable forestry and resources acquisition and recycling and not robbing the land and sea was probably one of the greatest invention by mankind (and no I'm not talking about gmo corporation mass farming) ....this happened probably in the turn of the last ice-age when human population began their 1st global population explosion, if not for this sustainable way to scale, we would be left hungry, sick, and as a species probably died of if we just destroy all flora and fauna vegetation eventually leading to our demise.....aka like Ester Island.

Without the great invention by early society, of sustainable food, water, shelter for the masses, like the Aboriginals of Australia, and the Native Americans, we would have perish and never advance to become a great civilization as we are today