3500 BC was the greatest era of invention.
Why 3500 BC, you ask?
The (approximate, of course) invention of beer.
Go ahead, tell me of a greater one. Can't, can ya?
People will no doubt laugh at this, but it's actually a good observation (though we should include wine in the list). The reason is simple: We humans need to ingest a fair amount of water each day to stay healthy. But historically, water itself has been rather dangerous stuff. Consider all the other people and animals upstream who have been using it for both bathing and disposing of waste of various sorts. Do you want to drink that water? Not if you want a long, healthy life.
Part of the year, our ancestors could get some of the needed water by consuming fruits, which are high in water. But they mostly don't keep very well, and they spoil. Fermented juices have their sugars partly converted to ethanol, which is toxic to most of the spoilage micro-organisms, so the resulting wine or beer is much less likely to spoil. (If it does, the result is often vinegar, which is another way of preserving the juice in a way that's safe for humans to consume).
It's pretty well understood among historians, anthropologists, etc., that fermentation processes were a significant part of our ancestors' development into a long-lived species that eventually dominated much of the planet. Yes, it's fun to get drunk, and to joke about getting drunk. And some other animals can get drunk, since ripe fruits often contain around 1% ethanol. (I've read some funny stories about groups of elephants getting a bit tipsy from the consumption of ripe fruit. Imagine a crowd of drunk elephants partying in your neighborhood. ;-) But the fact is that ethanol-laced liquids are historically an important part of our history, because ethanol provided a way to make those liquids safe to drink.
There was a fun study some time back, in which some researchers traveled around the world, stopping in various eateries, ordering food, and taking it back to their hotel room to feed to the lab equipment they'd brought along. They were testing it for safety (and ate the food that passed their tests ;-). Their main summary of their results was that, if you want a simple rule for ordering something safe to drink, no matter where you are, order beer. They didn't always like the beer everywhere, but their tests never found beer that was unsafe for human consumption. Wine was in second place, but they did find contaminated wine in a few places.
The explanation seems to be that, as anyone who has tried brewing beer knows, you have to be really careful about cleanliness during the brewing, or you get an awful-smelling glop that nobody will drink. With wine, the process seems easy, and you can get good-smelling wine by just letting the fruit juice (with perhaps added yeast) ferment, but sometimes the result has contaminants that aren't obvious. But with beer, this doesn't work; you have to boil it all to sterilize it, add a yeast culture, make sure that stuff floating in the air can't get into the containers, or everyone will know that you've failed the instant they sniff it. So beer probably is the most significant brewing achievement in human history.